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- Title
- Investigation of Real Gas Effects on Centrifugal Compressor Analytical Methods for Supercritical CO2 Power Cycles.
- Creator
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Blanchette, Lauren, Kapat, Jayanta, Kassab, Alain, Vasu Sumathi, Subith, University of Central Florida
- Abstract / Description
-
As supercritical carbon dioxide (sCO2) power cycles have shown potential to be the next generation power cycle, an immense amount of research has gone into developing this system. One of the setbacks facing development and optimization of this cycle is the unknown in current design and analysis methods ability to accurately model turbomachinery working with sCO2. Due to the desired inlet conditions to the compressor close proximity to the critical point, accurate design and analysis of this...
Show moreAs supercritical carbon dioxide (sCO2) power cycles have shown potential to be the next generation power cycle, an immense amount of research has gone into developing this system. One of the setbacks facing development and optimization of this cycle is the unknown in current design and analysis methods ability to accurately model turbomachinery working with sCO2. Due to the desired inlet conditions to the compressor close proximity to the critical point, accurate design and analysis of this power cycle component is one of the main concerns. The present study provides aerodynamic analysis of a centrifugal compressor impeller blade with sCO2 as the working fluid through a comparative study between three dimensional (3D) computational fluid dynamics (CFD) and a one dimensional (1D) mean line analyses. The main centrifugal compressor in reference to a 100 MW sCO2 closed loop Recuperated Recompression Brayton cycle is investigated. Through the use of conventional loss correlations for centrifugal compressors found in the literature, and geometrical parameters developed through a past mean line design, losses were calculated for the specified compressor impeller. The aerodynamic performance is then predicted through the 1D analysis. Furthermore, the boundary conditions for the CFD analysis were derived through the mean line analysis of the centrifugal compressor to carry out the 3D study of the sCO2 impeller blade. As the Span and Wagner equation of state has been proven to be the most accurate when working in the vicinity of the critical point, this real gas equation of state was implemented in both analyses. Consequently, a better understanding was developed on best practices for modeling a real gas sCO2 centrifugal compressor along with the limitations that currently exist when utilizing commercial CFD solvers. Furthermore, the resulting performance and aerodynamic behavior from the 1D analysis were compared with the predicted conclusions from the CFD analysis. Past literature studies on sCO2 compressor analysis methodology have been focused on small scale power cycles. This work served as the first comparison of 1D and 3D analysis methodology for large scale sCO2 centrifugal compressors. The lack of commercial CFD codes able to model phase change within sCO2 turbomachinery and the possible breach of flow properties into the saturation region at the leading edge of the impeller blade creates a limit to the operating conditions that can be simulated within these analysis tools. Further, the rapid expansion rate within this region has been predicted to cause non-equilibrium condensation leading the fluid to a metastable vapor state. Due to the complexity of two phase models, a proposed methodology to model sCO2 compressors as single phase is to represent metastable properties through the extrapolation of equilibrium properties onto the liquid domain up until the spinodal limit. This equation of state definition with metastable properties was used to model a 3D converging-diverging nozzle due to the similar flow dynamics occurring when compared to a compressor blade channel. The equation of state was implemented through a temperature and pressure dependent property table amended with metastable properties using the NIST REFPROP Database. Modeling was performed for inlet conditions with varied closeness to the fluid's critical point. Investigation on the accuracy of utilizing this table to define sCO2 properties with respect to its resolution was executed. Through this, it was determined that the resulting interpolation error was highly influenced on the closeness to the critical point. Additionally, the effect on the capable modeling operating region when utilizing the metastable real gas property table through single phase modeling was examined.
Show less - Date Issued
- 2016
- Identifier
- CFE0006442, ucf:51466
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006442
- Title
- Hydrodynamic Measurements of the Flow Structure Emanating From A Multi-Row Film Cooling Configuration.
- Creator
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Voet, Michael, Kapat, Jayanta, Vasu Sumathi, Subith, Ahmed, Kareem, University of Central Florida
- Abstract / Description
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The demand for more power is rapidly increasing worldwide. Attention is turned to increasingthe efficiency of modern methods for power generation. Gas turbines provide 35% of the powerdemands within the United States. Efficiency of gas turbines is defined in an ideal sense by thethermal efficiency of the Brayton Cycle. The overall efficiency of a gas turbine can be increased while simultaneously maximizing specific work output, by increasing the turbine inlet temperature. However, even with...
Show moreThe demand for more power is rapidly increasing worldwide. Attention is turned to increasingthe efficiency of modern methods for power generation. Gas turbines provide 35% of the powerdemands within the United States. Efficiency of gas turbines is defined in an ideal sense by thethermal efficiency of the Brayton Cycle. The overall efficiency of a gas turbine can be increased while simultaneously maximizing specific work output, by increasing the turbine inlet temperature. However, even with the advancements in modern materials in terms of maximum operatingtemperature, various components are already subjected to temperatures higher than their melting temperatures. An increase in inlet temperature would subject various components to even higher temperatures, such that more effective cooling would be necessary, whilst ideally using the same (or less) amount of cooling air bled from compressor. Improvements in the performance of these cooling techniques is thus required. The focus of this thesis is on one such advanced cooling technique, namely film cooling.The objective of this study is to investigate the effects of coolant density on the jet structure for different multi-row film cooling configurations. As research is performed on improving the performance of film cooling, the available conditions during testing may not reflect actual engine-like conditions. Typical operating density ratio at engine conditions are between 1.5 and 2, while it is observed that a majority of the density ratios tested in literature are between 1 and 1.5. While thesetests may be executed outside of engine-like conditions, it is important to understand how density ratio effects the flow physics and film cooling performance. The density ratio within this study is varied between 1.0 and 1.5 by alternating the injecting fluid between air and Carbon Dioxide, respectively.Both a simple cylindrical and fan-shape multi-row film cooling configuration are tested in the present study. In order to compare the results collected from these geometries, lateral and spanwise hole-to-hole spacing, metering hole diameter, hole length, and inclination angle are held constant between all testing configurations. The effect of fluid density upon injection is examined by independently holding either blowing, momentum flux, or velocity ratio constant whilst varying density ratio. Comparisons between both of the film cooling configurations are also made as similar ratios are tested between geometries. This allows the variation in flow structure and performance to be observed from alternating the film cooling hole shape.Particle Image Velocimetry (PIV) is implemented to obtain both streamwise and wall normal velocitymeasurements for the array centerline plane. This data is used to examine the interactionof the jet as it leaves the film cooling hole and the structure produced when the jet mixes with theboundary layer.Similarities in jet to jet interactions and surface attachment between density ratios are seen for the cylindrical configuration when momentum flux ratio is held constant. When observing constant blowing ratio comparisons of the cylindrical configurations, the lower density ratio is seen to begin detaching from the wall at M = 0.72 with little evidence of coolant in the near wall region. However, the higher density cylindrical injection retains its surface attachment at M = 0.74 with noticeably more coolant near the wall, because of significantly lower momentum flux ratio and lower (")jetting(") effect. The fan-shape film cooling configuration demonstrates improved performance, in terms of surface attachment, over a larger range of all ratios than that of the cylindrical cases. Additionally, the fan-shape configuration is shown to constantly retain a thicker layer of low velocity fluid in the near wall region when injected with the higher density coolant, suggesting improved performance at the higher density ratio.When tracking the jet trajectory, it is shown that the injection of CO2 through the cylindricalconfiguration yields a higher centerline wall normal height per downstream location than that of the lower density fluid. Comparing the results of the centerline tracking produced by the third and fifth rows for both the injection of air and CO2, it is confirmed that the fifth row of injection interacts with the boundary layer at a great wall normal height than that of the third row. Additionally, when observing the change in downstream trajectory between the fifth and seventh row of injection, a significant decrease in wall normal height is seen for the coolant produced by the seventh row. It is believed that the lack of a ninth row of injection allows the coolant from the seventh row of injection to remain closer to the target surface. This is further supported by the observation of the derived pressure gradient field and the path streamlines take while interacting with the recirculatory region produced by the injection of coolant into the boundary layer.Further conclusions are drawn by investigating the interaction between momentum thickness andthe influence of blowing ratio. Relatively constant downstream momentum thickness is observedfor the injection of lower density fluid for the blowing ratio range of M= 0.4 to 0.8 for the cylindrical configuration. It is suggested that a correlation exists between momentum thickness and film cooling performance, however further studies are needed to validate this hypothesis.
Show less - Date Issued
- 2017
- Identifier
- CFE0006817, ucf:51791
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006817
- Title
- Simultaneous Imaging of the Diatomic Carbon and Methylidyne Species Radicals for the Quantification of the Fuel to Air Ratio from Low to High Pressure Combustion.
- Creator
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Reyes, Jonathan, Ahmed, Kareem, Kassab, Alain, Kapat, Jayanta, University of Central Florida
- Abstract / Description
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The radical intensity ratio of the diatomic carbon to methylidyne was characterized at initialpressures up to 10 bar using certified gasoline of 93% octane. This gasoline was selected due toits availability as a common fuel. The characterization of the radical intensity ratio of gasoline atelevated pressures enabled the creation of a calibration map of the equivalence ratio at enginerelevant conditions.The proposed calibration map acts as a feedback loop for a combustor. It allows for...
Show moreThe radical intensity ratio of the diatomic carbon to methylidyne was characterized at initialpressures up to 10 bar using certified gasoline of 93% octane. This gasoline was selected due toits availability as a common fuel. The characterization of the radical intensity ratio of gasoline atelevated pressures enabled the creation of a calibration map of the equivalence ratio at enginerelevant conditions.The proposed calibration map acts as a feedback loop for a combustor. It allows for thelocation of local rich and lean zones. The local information acquired can be used as an optimizationparameter for injection and ignition timings, and future combustor designs. The calibration map isapplicable at low and high engine loads to characterize a combustors behavior at all points in itsoperation map.Very little emphasis has been placed on the radical intensity ratio of unsteady flames,flames at high pressure, and liquid fuels. The current work performed the measurement on anunsteady flame ignited at different initial pressures employing a constant volume combustionchamber and liquid gasoline as the fuel source. The chamber can sustain a pressure rise of 200 barand allows for homogenous fuel to air mixtures.The results produced a viable calibration map from 1 to 10 bar. The intensity ratio at initialpressures above 5 bar behaved adversely in comparison to the lower pressure tests. The acquiredratios at the higher initial pressures are viable as individual calibration curves, but created anunexpected calibration map. The data shows promise in creating a calibration map that is usefulfor practical combustors.
Show less - Date Issued
- 2017
- Identifier
- CFE0006910, ucf:51692
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006910
- Title
- FUNDAMENTAL UNDERSTANDING OF INTERACTIONS AMONG FLOW, TURBULENCE, AND HEAT TRANSFER IN JET IMPINGEMENT COOLING.
- Creator
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Hossain, Md. Jahed, Kapat, Jayanta, Ahmed, Kareem, Gordon, Ali, Wiegand, Rudolf, University of Central Florida
- Abstract / Description
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The flow physics of impinging jet is very complex and is not fully understood yet. The flow field in an impingement problem comprised of three different distinct regions: a free jet with a potential core, a stagnation region where the velocity goes to zero as the jet impinges onto the wall and a creation of wall jet region where the boundary layer grows radially outward after impinging. Since impingement itself is a broad topic, effort is being made in the current study to narrow down on...
Show moreThe flow physics of impinging jet is very complex and is not fully understood yet. The flow field in an impingement problem comprised of three different distinct regions: a free jet with a potential core, a stagnation region where the velocity goes to zero as the jet impinges onto the wall and a creation of wall jet region where the boundary layer grows radially outward after impinging. Since impingement itself is a broad topic, effort is being made in the current study to narrow down on three particular geometric configurations (a narrow wall, an array impingement configuration and a curved surface impingement configuration) that shows up in a typical gas turbine impingement problem in relation to heat transfer. Impingement problems are difficult to simulate numerically using conventional RANS models. It is worth noting that the typical RANS model contains a number of calibrated constants and these have been formulated with respect to relatively simple shear flows. As a result typically these isotropic eddy viscosity models fail in predicting the correct heat transfer value and trend in impingement problem where the flow is highly anisotropic. The common RANS-based models over predict stagnation heat transfer coefficients by as much as 300% when compared to measured values. Even the best of the models, the v^2-f model, can be inaccurate by up to 30%. Even though there is myriad number of experimental and numerical work published on single jet impingement; the knowledge gathered from these works cannot be applied to real engineering impingement cooling application as the dynamics of flow changes completely. This study underlines the lack of experimental flow physics data in published literature on multiple jet impingement and the author emphasized how important it is to have experimental data to validate CFD tools and to determine the suitability of Large Eddy Simulation (LES) in industrial application. In the open literature there is not enough study where experimental heat transfer and flow physics data are combined to explain the behavior for gas turbine impingement cooling application. Often it is hard to understand the heat transfer behavior due to lack of time accurate flow physics data hence a lot of conjecture has been made to explain the phenomena. The problem is further exacerbated for array of impingement jets where the flow is much more complex than a single round jet. The experimental flow field obtained from Particle Image Velocimetry (PIV) and heat transfer data obtained from Temperature Sensitive Paint (TSP) from this work will be analyzed to understand the relationship between flow characteristics and heat transfer for the three types of novel geometry mentioned above.There has not been any effort made on implementing LES technique on array impingement problem in the published literature. Nowadays with growing computational power and resources CFD are widely used as a design tool. To support the data gathered from the experiment, LES is carried out in narrow wall impingement cooling configuration. The results will provide more accurate information on impingement flow physics phenomena where experimental techniques are limited and the typical RANS models yield erroneous resultThe objective of the current study is to provide a better understanding of impingement heat transfer in relation to flow physics associated with it. As heat transfer is basically a manifestation of the flow and most of the flow in real engineering applications is turbulent, it is very important to understand the dynamics of flow physics in an impingement problem. The work emphasis the importance of understanding mean velocities, turbulence, jet shear layer instability and its importance in heat transfer application. The present work shows detailed information of flow phenomena using Particle Image Velocimetry (PIV) in a single row narrow impingement channel. Results from the RANS and LES simulations are compared with Particle Image Velocimetry (PIV) data. The accuracy of LES in predicting the flow field and heat transfer of an impingement problem is also presented the in the current work as it is validated against experimental flow field measured through PIV.Results obtained from the PIV and LES shows excellent agreement for predicting both heat transfer and flow physics data. Some of the key findings from the study highlight the shortcomings of the typical RANS models used for the impingement heat transfer problem. It was found that the stagnation point heat transfer was over predicted by as much as 48% from RANS simulations when compared to the experimental data. A lot of conjecture has been made in the past for RANS' ability to predict the stagnation point heat transfer correctly. The length of the potential core for the first jet was found to be ~ 2D in RANS simulations as oppose to 1D in PIV and LES, confirm the possible underlying reason for this discrepancy. The jet shear layer thickness was underpredicted by ~ 40% in RANS simulations proving the model is not diffusive enough for a flow like jet impingement. Turbulence production due to shear stress was over predicted by ~130% and turbulence production due to normal stresses were underpredicted by ~40 % in RANS simulation very close to the target wall showing RANS models fail where both strain rate and shear stress plays a pivotal role in the dynamics of the flow. In the closing, turbulence is still one of the most difficult problems to solve accurately, as has been the case for about a century. A quote below from the famous mathematician, Horace Lamb (1849-1934) express the level of difficulty and frustration associated with understanding turbulence in fluid mechanics. (")I am an old man now, and when I die and go to heaven there are two matters on which I hope for enlightenment. One is quantum electrodynamics, and the other is the turbulent motion of fluids. And about the former I am rather optimistic.(")Source: http://scienceworld.wolfram.com/biography/Lamb.htmlThis dissertation is expected to shed some light onto one specific example of turbulent flows.
Show less - Date Issued
- 2016
- Identifier
- CFE0006463, ucf:51424
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006463
- Title
- Characterization of SLM-Manufactured Turbine Blade Microfeatures from Superalloy Powders.
- Creator
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Ealy, Brandon, Kapat, Jayanta, Ahmed, Kareem, Vasu Sumathi, Subith, University of Central Florida
- Abstract / Description
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The limits of gas turbine technology are heavily influenced by materials and manufacturing capabilities. Inconel remains the material of choice for most hot gas path (HGP) components in gas turbines, however recent increases in turbine inlet temperature (TIT) are associated with the development of advanced convective cooling methods and ceramic thermal barrier coatings. Increasing cycle efficiency and cycle specific work are the primary drivers for increasing TIT. Lately, incremental...
Show moreThe limits of gas turbine technology are heavily influenced by materials and manufacturing capabilities. Inconel remains the material of choice for most hot gas path (HGP) components in gas turbines, however recent increases in turbine inlet temperature (TIT) are associated with the development of advanced convective cooling methods and ceramic thermal barrier coatings. Increasing cycle efficiency and cycle specific work are the primary drivers for increasing TIT. Lately, incremental performance gains responsible for increasing the allowable TIT have been made mainly through innovations in cooling technology, specifically convective cooling schemes. An emerging manufacturing technology may further facilitate the increase of allowable maximum TIT, thereby impacting cycle efficiencies. Laser Additive Manufacturing (LAM) is a promising manufacturing technology that uses lasers to selectively melt powders of metal in a layer-by-layer process to directly manufacture components, paving the way to produce designs that are not possible with conventional casting methods. This study investigates manufacturing qualities seen in LAM methods and its ability to successfully produce complex microfeatures in a mock turbine blade leading edge. Various cooling features are incorporated in design, consisting of internal impingement cooling, internal lattice structures, and external showerhead cooling. The internal structure is designed as a lattice of intersecting cylinders in order to mimic that of a porous material. Through a non-destructive approach, the presented design is analyzed against the departure of the design by utilizing X-ray computed tomography (CT). Employing this non-destructive testing (NDT) method, a more thorough analysis of the quality of manufacture is established by revealing the internal structures of the porous region and internal impingement array. Variance distribution between the design and manufactured test article are carried out for both internal impingement and external transpiration hole diameters from CT data. Flow testing is performed to characterize the uniformity of porous regions and flow behavior across the entire article for various pressure ratios. Discharge coefficients of internal impingement arrays and porous structures are quantified. A numerical model of fluid flow through the exact CAD geometry is analyzed over the range of experimental flowrates. By comparison of experimental and numerical data, performance discrepancies associated with manufacturing quality are observed. Simplifying assumptions to the domain are evaluated to compare predictions of CFD using the exact geometry. This study yields quantitative data on the build quality of the LAM process, providing more insight as to whether it is a viable option for manufacture of micro-features in current turbine blade production.
Show less - Date Issued
- 2016
- Identifier
- CFE0006452, ucf:51428
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006452
- Title
- Characterization of Fast Flames for Turbulence-Induced Deflagration to Detonation Transition.
- Creator
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Chambers, Jessica, Ahmed, Kareem, Kapat, Jayanta, Kassab, Alain, University of Central Florida
- Abstract / Description
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One of the fundamental mechanisms for detonation initiation is turbulence driven deflagration to detonation transition (TDDT). The research experimentally explores the propagation dynamics demonstrated by fast deflagrated flames interacting with highly turbulent reactants. Fast flames produce extremely high turbulent flame speeds values, increased levels of compressibility and develop a runaway mechanism that leads to TDDT. The flame structural dynamics and reacting flow field are...
Show moreOne of the fundamental mechanisms for detonation initiation is turbulence driven deflagration to detonation transition (TDDT). The research experimentally explores the propagation dynamics demonstrated by fast deflagrated flames interacting with highly turbulent reactants. Fast flames produce extremely high turbulent flame speeds values, increased levels of compressibility and develop a runaway mechanism that leads to TDDT. The flame structural dynamics and reacting flow field are characterized using simultaneous high-speed particle image velocimetry, chemiluminescence, and Schlieren measurements. The investigation classifies the fast flame propagation modes at various regimes. The study further examines the conditions for a turbulent fast flame at the boundary of transitioning to quasi-detonation. The evolution of the flame-compressibility interactions for this turbulent fast flame is characterized. The local measured turbulent flame speed is found to be greater than the Chapman(-)Jouguet deflagration flame speed which categorizes the flame to be at the spontaneous transition regime and within the deflagration-to-detonation transition runaway process.
Show less - Date Issued
- 2018
- Identifier
- CFE0006985, ucf:51642
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006985
- Title
- High Temperature Shock Tube Ignition Studies of CO2 Diluted Mixtures.
- Creator
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Pryor, Owen, Vasu Sumathi, Subith, Kapat, Jayanta, Kassab, Alain, University of Central Florida
- Abstract / Description
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Energy demand is expected to grow by 20% over the next 10 years. In order to account for this increase in energy consumption new and novel combustion techniques are required to mitigate the effects of pollution and fossil fuel dependency. Oxy-fuel combustion in supercritical carbon dioxide (sCO2) cycles can increase plant efficiencies up to 52% and reduce pollutants such as NOX and CO2 by 99%. Supercritical engine cycles have demonstrated electricity costs of $121/MWh, which is competitive in...
Show moreEnergy demand is expected to grow by 20% over the next 10 years. In order to account for this increase in energy consumption new and novel combustion techniques are required to mitigate the effects of pollution and fossil fuel dependency. Oxy-fuel combustion in supercritical carbon dioxide (sCO2) cycles can increase plant efficiencies up to 52% and reduce pollutants such as NOX and CO2 by 99%. Supercritical engine cycles have demonstrated electricity costs of $121/MWh, which is competitive in comparison to conventional coal ($95.60/MWh) and natural gas power plants ($128.4/MWe). This increase in efficiency is mainly driven by the near-liquid density of the working fluid (sCO2), in the super critical regime, before entering the turbine for energy extraction of the high pressure and high density sCO2 gas. In addition, supercritical CO2 engine cycles produce near-zero air emissions since CO2, a product of combustion, is the working fluid of the system which can be regenerated to the combustor. The predictive accuracy and lack of combustion models in highly CO2 diluted mixtures and at high pressures is one the major limitations to achieving optimum design of super critical engine combustors. Also, most natural gas mechanisms and validation experiments have been conducted at low pressures (typically less than 40 atm) and not in CO2 diluted environment. Thus experimental data is important for the development of modern combustion systems from work focusing on supercritical carbon dioxide cycles to rotational detonation engines. This thesis presents the design of the shock tube and two optical diagnostic techniques for measuring ignition delay times and species time histories using a shock tube in CO2 diluted mixtures.Experimental data for ignition delay times and species time-histories (CH4) were obtained in mixtures diluted with CO2. Experiments were performed behind reflected shockwaves from temperatures of 1200 to 2000 K for pressures ranging from 1 to 11 atm. Ignition times were obtained from emission and laser absorption measurements. Current experimental data were compared with the predictions of detailed chemical kinetic models (available from literature) that will allow for accurate design and modeling of combustion systems.
Show less - Date Issued
- 2016
- Identifier
- CFE0006165, ucf:51141
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006165
- Title
- Non-Dispersive Infrared (NDIR) Gas Sensor Utilizing Light-Emitting-Diodes Suitable for Applications Demanding Low-Power and Lightweight Instruments.
- Creator
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Thurmond, Kyle, Vasu Sumathi, Subith, Kassab, Alain, Kapat, Jayanta, University of Central Florida
- Abstract / Description
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Gas sensors that are low-power, light-weight, and rugged, while also remaining low-cost, have considerable appeal to areas from automotive to space flight. There are increasing demands for higher efficient vehicles with lower emissions in order meet regulations that are meant to mitigate or lessen the effects of climate change. An affordable, fast response sensor that can measure transient carbon monoxide (CO) and carbon dioxide (CO2) has broad application which can lead to more efficient,...
Show moreGas sensors that are low-power, light-weight, and rugged, while also remaining low-cost, have considerable appeal to areas from automotive to space flight. There are increasing demands for higher efficient vehicles with lower emissions in order meet regulations that are meant to mitigate or lessen the effects of climate change. An affordable, fast response sensor that can measure transient carbon monoxide (CO) and carbon dioxide (CO2) has broad application which can lead to more efficient, fuel flexible engines and regulations of harmful emissions. With compact, economical, low-power sensors that are able to continually monitor gases that are characteristic of burning materials, a distributed sensor array could be implemented on space vehicles that would allow early detection of fires, gas leaks, or other critical events. With careful selection of targeted gases, it may be possible to identify the material that is burning or smoldering, better informing the crew so that they may respond and prioritize high emergency events. Further applications may include fuel/ hazardous gas leak detection on space vehicles and atmospheric constituent sensor for portable life support systems (PLSS) used by astronauts in extra vehicular activity (EVA). Non-dispersive infrared (NDIR) sensors are attractive due to their simplicity and low-cost; and by using light-emitting-diodes (LEDs) in this approach, power efficient, light-weight, and stable gas sensors can be developed to meet these needs.This thesis discusses a sensor that was developed for simultaneous, time resolved measurements of carbon monoxide (CO) and carbon dioxide (CO2). This sensor utilizes low-cost and compact light emitting diodes (LEDs) that emit in the 3-5?m wavelength range. Light emission of LEDs is spectrally broader and more spatially divergent compared to that of lasers, which presented many design challenges. Optical design studies addressed some of the non-ideal characteristics of the LED emissions. Measurements of CO and CO2 were conducted using their fundamental absorption bands centered at 4.7?m and 4.3?m, respectively, while a 3.6?m reference LED was used to account for scattering losses (e.g., due to soot, window deposits, etc.) common to the three measurement LEDs. Instrument validation and calibration was performed using a laboratory flow cell and bottled-gas mixtures. The sensor was able to detect CO2 and CO concentration changes as small as 30 ppm and 400 ppm, respectively. Because of the many control and monitor species with infra-red absorption features, which can be measured using the strategy described, this work demonstrates proof of concept for a wider range of fast (250Hz) and low cost sensors for gas measurement and process monitoring.
Show less - Date Issued
- 2016
- Identifier
- CFE0006190, ucf:51091
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006190
- Title
- Comparison of Modeling Methods for Power Cycle Components Using Supercritical Carbon Dioxide as the Operating Fluid.
- Creator
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Schmitt, Joshua, Kapat, Jayanta, Kassab, Alain, Vasu Sumathi, Subith, University of Central Florida
- Abstract / Description
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Supercritical carbon dioxide as a working fluid in a Brayton power cycle has benefits but also faces unique challenges in implementation. With carbon dioxide, turbomachinery is much more compact and potentially more cost effective. The primary impediments to cycle component performance are the high pressures required to bring the fluid to a supercritical state and the wildly varying fluid properties near the critical point. Simple design models are often used as a quick starting point for...
Show moreSupercritical carbon dioxide as a working fluid in a Brayton power cycle has benefits but also faces unique challenges in implementation. With carbon dioxide, turbomachinery is much more compact and potentially more cost effective. The primary impediments to cycle component performance are the high pressures required to bring the fluid to a supercritical state and the wildly varying fluid properties near the critical point. Simple design models are often used as a quick starting point for modern turbomachinery and heat exchanger design. These models are reasonably accurate for design estimate, but often assume constant properties. Since supercritical carbon dioxide varies not only in temperature, but also in pressure, the models must be evaluated for accuracy. Two key factors in cycle design, aerodynamics and heat transfer, are investigated through the modeling of the performance of the first stage of the turbo-expander and the recuperative heat exchangers. Lookup tables that define the change in fluid properties relative to changes in pressure and temperature are input into the fluid dynamics software. The results of the design models are evaluated against each other. The simpler models and the fluid dynamics simulations are found to have acceptable agreement. Improvements to the simple models are suggested.
Show less - Date Issued
- 2015
- Identifier
- CFE0006229, ucf:51085
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006229
- Title
- Development of Velocity Profile Generating Screens for Gas Turbine Components.
- Creator
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Tate, Joseph, Kapat, Jayanta, Gordon, Ali, Ahmed, Kareem, University of Central Florida
- Abstract / Description
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Laboratory experiments on components of complex systems such as gas turbines require many conditions to be met. Requirements to be met in order to simulate real world conditions include inlet flow conditions such as velocity profile, Reynold's number, and temperature. The methodology to be introduced designs a velocity profile generating screen to match real world conditions through the use of perforated plates. The velocity profile generating screen is an array of jets arranged in a manner...
Show moreLaboratory experiments on components of complex systems such as gas turbines require many conditions to be met. Requirements to be met in order to simulate real world conditions include inlet flow conditions such as velocity profile, Reynold's number, and temperature. The methodology to be introduced designs a velocity profile generating screen to match real world conditions through the use of perforated plates. The velocity profile generating screen is an array of jets arranged in a manner to produce sections of different solidities, a ratio of area that obstructs fluid flow compared to that of the total area. In an effort to better understand the interaction between perforated plate sections of different solidities, a collection of experimental data sets is presented to characterize the plates. This includes identification of fluid flow regions with characterization of the flow dynamics, though the analysis of velocity and turbulence decay. The aim of this characterization is to determine how the perforated plate's solidity affects the velocity development downstream and the location at which the velocity profile being produced can be considered complete.
Show less - Date Issued
- 2015
- Identifier
- CFE0006011, ucf:51020
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006011
- Title
- Statistical Analysis of Multi-Row Film Cooling Flowfields.
- Creator
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Fernandes, Craig, Kapat, Jayanta, Ahmed, Kareem, Vasu Sumathi, Subith, University of Central Florida
- Abstract / Description
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A huge part of modern day power generation research and development strives to achievehigher thermal efficiencies and specific work outputs for both gas turbine Brayton and combinedcycles. Advances in cooling technologies, both internal to turbine blades and external, provide the easiest way to accomplish this by raising the turbine inlet temperature far beyond the super-alloy's allowable temperature. Discrete film cooling injection, an external cooling technique, ensures a cool blanket of...
Show moreA huge part of modern day power generation research and development strives to achievehigher thermal efficiencies and specific work outputs for both gas turbine Brayton and combinedcycles. Advances in cooling technologies, both internal to turbine blades and external, provide the easiest way to accomplish this by raising the turbine inlet temperature far beyond the super-alloy's allowable temperature. Discrete film cooling injection, an external cooling technique, ensures a cool blanket of compressed air protects the blade surface from the harsh mainstream gas. To optimize the coverage and effectiveness of the film, a thorough understanding of the behavior andflow physics is necessary.The objective of the current study is to use hotwire anemometry as a tool to conduct 1D timeresolved turbulent measurements on the flow field of staggered multi-row film cooling arrays withcylindrical and diffuser shaped holes inclined at 20 degrees to the freestream. The study aims toinvestigate the flowfield to determine why the performance of diffuser shaped jets is enhanced even at comparatively high blowing ratios. In addition, blowing ratio effects and flowfield discrepanciesat set downstream locations in the array centerline plane are also investigated.The experiments are conducted on an open-loop wind tunnel for blowing ratios in the rangeof 0.3 to 1.5 at a density ratio of 1. Boundary layer measurements were taken at 12 locations atthe array centerline to obtain mean velocity, turbulence level, turbulence intensity, and integral length scales. Measurements were also taken at a location upstream of the array to characterize the incoming boundary layer and estimate the wall normal position of the probe in comparison with the logarithmic law of the wall.Mean effective velocity profiles were found to scale with blowing ratio for both geometries.A strong dependence of turbulence levels on velocity gradients between jets and the local fluid was also noticed. For cylindrical jets, attached cases displayed lower integral length scales in the nearwall region compared with higher blowing ratio cases. This was found to be due to entrainmentof mainstream fluid showing increased momentum transport below the jets. Diffuser cases atall blowing ratios tested do not show increased length scales near the wall demonstrating theirenhanced surface coverage. Row-to-row discrepancies in mean velocity and turbulence level are only evident at extremely high blowing cases for cylindrical, but show significant deviations for diffuser cases at all blowing ratios.Unlike the cylindrical cases, jets from diffuser shaped holes, due to their extremely low injecting velocities, dragged the boundary layer with each row of blowing. Increased velocity gradients create a rise in peak turbulence levels at downstream locations. At high blowing ratios however, faster moving fluid, due to injection, at lower elevations acts as a shield for downstream jets allowing significantly further propagation downstream. Near the wall low magnitude integral length scales are noticed for diffuser jets indicating low momentum transport in this region.The results show good agreement with effectiveness measurements of a previous study at a higher density ratio. However, to accurately draw the comparison, effectiveness measurements should be conducted at a density ratio of 1. Recommendations were made to further the study of multi-row film cooled boundary layers. The scope includes a CFD component, other flowfield measurement techniques, and surface effectiveness studies using Nitrogen as the coolant for a much broader picture of this flowfield.
Show less - Date Issued
- 2017
- Identifier
- CFE0006738, ucf:51863
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006738
- Title
- Coupled Usage of Discrete Hole and Transpired Film For Better Cooling Performance.
- Creator
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Torrance, Michael, Kapat, Jayanta, Vasu Sumathi, Subith, Xu, Chengying, University of Central Florida
- Abstract / Description
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Electricity has become so ingrained in everyday life that the current generation has no knowledge of life without it. The majority of power generation in the United States is the result of turbines of some form. With such widespread utilization of these complex rotating machines, any increase in efficiency translates into improvements in the current cost of energy. These improvements manifest themselves as reductions in greenhouse emissions or possible savings to the consumer. The most...
Show moreElectricity has become so ingrained in everyday life that the current generation has no knowledge of life without it. The majority of power generation in the United States is the result of turbines of some form. With such widespread utilization of these complex rotating machines, any increase in efficiency translates into improvements in the current cost of energy. These improvements manifest themselves as reductions in greenhouse emissions or possible savings to the consumer. The most important temperature regarding turbine performance is the temperature of the hot gas entering the turbine, denoted turbine inlet temperature. Increasing the turbine inlet temperature allows for increases in power production as well as increases in efficiency. The challenge with increasing this temperature, currently the hottest temperature seen by the turbine, is that it currently already exceeds the melting point of the metals that the turbine is manufactured from. Active cooling of stationary and rotating components in the turbine is required. Cooling flows are taken from bleed flows from various stages of the compressor as well as flow from the combustor shell. This cooling flow is considered wasted air as far as performance is concerned and can account for as much as 20% of the mass flow in the hot gas path. Lowering the amount of air used for cooling allows for more to be used for performance gain.Various technologies exist to allow for greater turbine inlet temperatures such as various internal channel features inside of turbine blades, film holes on the surface to cool the outside of the airfoil as well as thermal barrier coatings that insulate the airfoils from the hot mainstream flow. The current work is a study of the potential performance impact of coupling two effusion technologies, transpiration and discrete hole film cooling. Film cooling and transpiring flows are individually validated against literature before the two technologies are coupled. The coupled geometries feature 13 film holes of 7.5mm diameter and a transpiring strip 5mm long in the streamwise direction. The first coupled geometry features the porous section upstream of the film holes and the second features it downstream. Both geometries use the same crushed aluminum porous insert of nominal porosity of 50%. Temperature sensitive paint along with an 'adiabatic' Rohacell surface (thermal conductivity of 0.029W/m-K) are used to measure adiabatic film cooling effectiveness using a scientific grade high resolution CCD camera. The result is local effectiveness data up to 50 film hole diameters downstream of injection location. Data is laterally averaged and compared with the baseline cases. Local effectiveness contours are used to draw conclusions regarding the interactions between transpiration and discrete hole film cooling. It is found that a linear superposition method is only valid far downstream from the injection location. Both coupled geometries perform better than transpiration or the discrete holes far downstream of the injection location. The coupled geometry featuring the transpiring section downstream of the film holes matches the transpiration effectiveness just downstream of injection and surpasses both transpiration and film cooling further downstream.
Show less - Date Issued
- 2012
- Identifier
- CFE0004799, ucf:49721
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004799
- Title
- A Full Coverage Film Cooling Study: The Effect of an Alternating Compound Angle.
- Creator
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Hodges, Justin, Kapat, Jayanta, Gordon, Ali, Vasu Sumathi, Subith, University of Central Florida
- Abstract / Description
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This thesis is an experimental and numerical full-coverage film cooling study. The objective of this work is the quantification of local heat transfer augmentation and adiabatic film cooling effectiveness for two full-coverage film cooling geometries. Experimental data was acquired with a scientific grade CCD camera, where images are taken over the heat transfer surface, which is painted with a temperature sensitive paint. The CFD component of this study served to evaluate how well the v2-f...
Show moreThis thesis is an experimental and numerical full-coverage film cooling study. The objective of this work is the quantification of local heat transfer augmentation and adiabatic film cooling effectiveness for two full-coverage film cooling geometries. Experimental data was acquired with a scientific grade CCD camera, where images are taken over the heat transfer surface, which is painted with a temperature sensitive paint. The CFD component of this study served to evaluate how well the v2-f turbulence model predicted film cooling effectiveness throughout the array, as compared with experimental data. The two staggered arrays tested are different from one another through a compound angle shift after 12 rows of holes. The compound angle shifts from ?=-45(&)deg; to ?=+45(&)deg; at row 13. Each geometry had 22 rows of cylindrical film cooling holes with identical axial and lateral spacing (X/D=P/D=23). Levels of laterally averaged film cooling effectiveness for the superior geometry approach 0.20, where the compound angle shift causes a decrease in film cooling effectiveness. Levels of heat transfer augmentation maintain values of nearly h/h0=1.2. There is no effect of compound angle shift on heat transfer augmentation observed. The CFD results are used to investigate the detrimental effect of the compound angle shift, while the SST k-? turbulence model shows to provide the best agreement with experimental results.
Show less - Date Issued
- 2015
- Identifier
- CFE0005626, ucf:50228
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005626
- Title
- Processing and Characterization of Continuous Basalt Fiber Reinforced Ceramic Matrix Composites Using Polymer Derived Ceramics.
- Creator
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Cox, Sarah, Gou, Jihua, Kapat, Jayanta, Sohn, Yongho, University of Central Florida
- Abstract / Description
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The need for high performance vehicles in the aerospace industry requires materials which can withstand high loads and high temperatures. New developments in launch pads and infrastructure must also be made to handle this intense environment with lightweight, reusable, structural materials. By using more functional materials, better performance can be seen in the launch environment, and launch vehicle designs which have not been previously used can be considered. The development of high...
Show moreThe need for high performance vehicles in the aerospace industry requires materials which can withstand high loads and high temperatures. New developments in launch pads and infrastructure must also be made to handle this intense environment with lightweight, reusable, structural materials. By using more functional materials, better performance can be seen in the launch environment, and launch vehicle designs which have not been previously used can be considered. The development of high temperature structural composite materials has been very limited due to the high cost of the materials and the processing needed. Polymer matrix composites can be used for temperatures up to 260(&)deg;C. Ceramics can take much higher temperatures, but they are difficult to produce and form in bulk volumes. Polymer Derived Ceramics (PDCs) begin as a polymer matrix, allowing a shape to be formed and cured and then to be pyrolized in order to obtain a ceramic with the associated thermal and mechanical properties. The use of basalt in structural and high temperature applications has been under development for over 50 years, yet there has been little published research on the incorporation of basalt fibers as a reinforcement in the composites. In this study, continuous basalt fiber reinforced PDCs have been fabricated and tested for the applicability of this composite system as a high temperature structural composite material. The oxyacetylene torch testing and three point bend testing have been performed on test panels and the test results are presented.
Show less - Date Issued
- 2014
- Identifier
- CFE0005320, ucf:50530
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005320
- Title
- Development of Full Surface Transient Thermochromic Liquid Crystal Technique for Internal Cooling Channels.
- Creator
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Tran, Lucky, Kapat, Jayanta, Kassab, Alain, Vasu Sumathi, Subith, University of Central Florida
- Abstract / Description
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Proper design of high performance industrial heat transfer equipment relies on accurate knowledge and prediction of the thermal boundary conditions. In order to enhance the overall gas turbine efficiency, advancements in cooling technology for gas turbines and related applications are continuously investigated to increase the turbine inlet temperature without compromising the durability of the materials used. For detailed design, local distributions are needed in addition to bulk quantities....
Show moreProper design of high performance industrial heat transfer equipment relies on accurate knowledge and prediction of the thermal boundary conditions. In order to enhance the overall gas turbine efficiency, advancements in cooling technology for gas turbines and related applications are continuously investigated to increase the turbine inlet temperature without compromising the durability of the materials used. For detailed design, local distributions are needed in addition to bulk quantities. Detailed local distributions require advanced experimental techniques whereas they are readily available using numerical tools. Numerical predictions using a computational fluid dynamics approach with popular turbulence models are benchmarked against a semi-empirical correlation for the friction in a circular channel with repeated-rib roughness to demonstrate some shortcomings of the models used. Numerical predictions varied widely depending on the turbulence modelling approach used. The need for a compatible experimental dataset to accompany numerical simulations was discussed.An exact, closed-form analytical solution to the enhanced lumped capacitance model is derived. The temperature evolution in a representative 2D turbulated surface is simulated using Fluent to validate the model and its exact solution. A case including an interface contact resistance was included as well as various rib sizes to test the validity of the model over a range of conditions. The analysis was extended to the inter-rib region to investigate the extent and magnitude of the influence of the metallic rib features on the apparent heat transfer coefficients in the inter-rib region. It was found that the thermal contamination is limited only to the regions closest to the base of the rib feature.An experimental setup was developed, capable of measuring the local heat transfer distributions on all four channel walls of a rectangular channel (with aspect ratios between 1 and 5) at Reynolds numbers up to 150,000. The setup utilizes a transient thermochromic liquid crystals technique using narrow band crystals and a four camera setup. The setup is used to test a square channel with ribs applied to one wall. Using the transient thermochromic liquid crystals technique and applying it underneath high conductivity, metallic surface features, it is possible to calculate the heat transfer coefficient using a lumped heat capacitance approach. The enhanced lumped capacitance model is used to account for heat conduction into the substrate material. Rohacell and aluminum ribs adhered to the surface were used to tandem to validate the hybrid technique against the standard technique. Local data was also used to investigate the effect of thermal contamination. Thermal contamination observed empirically was more optimistic than numerical predictions.Traditional transient thermochromic liquid crystals technique utilizes the time-to-arrival of the peak intensity of the green color signal. The technique has been extended to utilize both the red and green color signals, increasing the throughput by recovering unused data while also allowing for a reduction in the experimental uncertainty of the calculated heat transfer coefficient. The over-determined system was solved using an un-weighted least squares approach. Uncertainty analysis of the multi-color technique demonstrated its superior performance over the single-color technique. The multi-color technique has the advantage of improved experimental uncertainty while being easy to implement.
Show less - Date Issued
- 2014
- Identifier
- CFE0005430, ucf:50436
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005430
- Title
- Development and Characterization of Nanoparticlee Enhancements in Pyrolysis-Derived High Temperature Composites.
- Creator
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McKee, James, Gou, Jihua, Kapat, Jayanta, Xu, Chengying, University of Central Florida
- Abstract / Description
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Thermal protection systems, which are commonly used to protect spacecraft during atmospheric entry, have traditionally been made of materials which are traditionally high in manufacturing costs for both the materials needed and the manufacturing complexity, such as carbon-carbon composites and aerogels. In addition to their manufacturing costs, these materials are also limited in their strength, such as PICA, in a way that necessitate the use of tiles as opposed to single structures because...
Show moreThermal protection systems, which are commonly used to protect spacecraft during atmospheric entry, have traditionally been made of materials which are traditionally high in manufacturing costs for both the materials needed and the manufacturing complexity, such as carbon-carbon composites and aerogels. In addition to their manufacturing costs, these materials are also limited in their strength, such as PICA, in a way that necessitate the use of tiles as opposed to single structures because they are not capable of supporting larger structures. The limitations of polymer reinforced composites have limited their entry into these applications, except for pyrolyzed composite materials, such as carbon-carbon and ceramic composites. These materials have been successfully demonstrated their utility in extreme environments, such as spacecraft heat shields, but their high costs and the difficulty to manufacture them have limited their use to similarly high performance applications where the costs are justifiable. Previous work by others with (")fuzzy fiber(") composites have shown that aligned carbon nanotubes (CNTs) grown on fibers can improve their thermal conductivity and wettability. To this end vertically aligned CNTs were studied for their potential use, but found to be difficult to process with current conventional techniques. A composite material comprised of basalt, a relatively new reinforcing fiber, and phenolic, which has been used in high-temperature applications with great success was made to attempt to create a new material for these applications. To further improve upon the favorable properties of the resulting composite, the composite was pyrolyzed to produce a basalt-carbon composite with a higher thermal stability than its pristine state. While testing the effects of pyrolysis on the thermal stability, a novel technique was also developed to promote in-situ carbon nanotube growth of the resulting basalt-carbon composite without using a monolithic piece of cured phenolic resin in place of the standard aromatic hydrocarbon-catalyst precursor. The in-situ growth of carbon nanotubes (CNTs) was explored as their thermal stability and effectiveness in improving performance has been previously demonstrated when used as a resin additive. The specimens were examined with SEM, EDS, and TGA to determine the effects of both pyrolysis and CNT growth during pyrolysis of the basalt phenolic composites. These tests would confirm the presence of CNTs/CNFs directly grown in the composite by pyrolysis, and confirm their composition by EDS and Raman spectroscopy. EDS would additionally confirm that the surface of the basalt fibers possess a composition suitable for CNT growth, similar to the parameters of CVD processing. Additional testing would also show that the growth behavior of the CNTs/CNFs is dependent on temperature as opposed to composition, indicating that there is a threshold temperature necessary to facilitate the availability of catalysts from within the basalt fibers. The thermal stability shown by TGA indicates that the process of pyrolysis leaves the newly formed composite with a high degree of thermal stability, making the new materials potentially usable in applications such as turbines, in addition to large-scale thermal protection systems.
Show less - Date Issued
- 2013
- Identifier
- CFE0005380, ucf:50458
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005380
- Title
- Experimental and Numerical Investigation of Aerodynamic Unsteadiness in a Gas Turbine Midframe.
- Creator
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Golsen, Matthew, Kapat, Jayanta, Vasu Sumathi, Subith, Sultanian, Bijay, University of Central Florida
- Abstract / Description
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As modern gas turbines implement more and more complex geometry to increase life and efficiency, attention to unsteady aerodynamic behavior becomes more important. Computational optimization schemes are contributing to advanced geometries in order to reduce aerodynamic losses and increase the life of components. These advanced geometries are less representative of cylinder and backward facing steps which have been used as analogous geometries for most aerodynamic unsteadiness research. One...
Show moreAs modern gas turbines implement more and more complex geometry to increase life and efficiency, attention to unsteady aerodynamic behavior becomes more important. Computational optimization schemes are contributing to advanced geometries in order to reduce aerodynamic losses and increase the life of components. These advanced geometries are less representative of cylinder and backward facing steps which have been used as analogous geometries for most aerodynamic unsteadiness research. One region which contains a high degree of flow unsteadiness and a direct influence on engine performance is that of the MidFrame. The MidFrame (or combustor-diffuser system) is the region encompassing the main gas path from the exit of the compressor to the inlet of the first stage turbine. This region contains myriad flow scenarios including diffusion, bluff bodies, direct impingement, high degree of streamline curvature, separated flow, and recirculation. This represents the most complex and diverse flow field in the entire engine. The role of the MidFrame is to redirect the flow from the compressor into the combustion system with minimal pressure loss while supplying high pressure air to the secondary air system. Various casing geometries, compressor exit diffuser shapes, and flow conditioning equipment have been tested to reduce pressure loss and increase uniformity entering the combustors. Much of the current research in this area focuses on aero propulsion geometries with annular combustors or scaled models of the power generation geometries. Due to the complexity and size of the domain accessibility with physical probe measurements becomes challenging. The current work uses additional measurement techniques to measure flow unsteadiness in the domain. The methodology for identifying and quantifying the sources of unsteadiness are developed herein. Sensitivity of MidFrame unsteadiness to compressor exit conditions is shown for three different velocity profiles. The result is an extensive database of measurements which can serve as a benchmark for radical new designs to ensure that the unsteadiness levels do not supersede previous successful levels.
Show less - Date Issued
- 2013
- Identifier
- CFE0004851, ucf:49682
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004851
- Title
- In-situ synchrotron studies of turbine blade thermal barrier coatings under extreme environments.
- Creator
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Knipe, Kevin, Raghavan, Seetha, Gordon, Ali, Kapat, Jayanta, Sohn, Yongho, University of Central Florida
- Abstract / Description
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Thermal Barrier Coatings have been used for decades to impose a thermal gradient between the hot combustion gases and the underlying superalloy substrate in engine turbine blades. Yttria Stabilized Zirconia (YSZ) is an industry standard high temperature ceramic for turbine applications. The protective coating is adhered to the substrate using a nickel based alloy bond coat. Through exposure to high temperature, a Thermally Grown Oxide (TGO) layer develops at the bond coat-YSZ interface. Large...
Show moreThermal Barrier Coatings have been used for decades to impose a thermal gradient between the hot combustion gases and the underlying superalloy substrate in engine turbine blades. Yttria Stabilized Zirconia (YSZ) is an industry standard high temperature ceramic for turbine applications. The protective coating is adhered to the substrate using a nickel based alloy bond coat. Through exposure to high temperature, a Thermally Grown Oxide (TGO) layer develops at the bond coat-YSZ interface. Large residual stresses develop in these layers due to thermal expansion mismatch that occurs during cool down from high temperature spraying and cyclic operating conditions. Despite their standard use, much is to be determined as to how these residual stresses are linked to the various failure modes. This study developed techniques to monitor the strain and stress in these internal layers during thermal gradient and mechanical conditions representing operating conditions. The thermal gradient is applied across the coating thickness of the tubular samples from infrared heating of the outer coating and forced air internal cooling of the substrate. While thermal and mechanical loading conditions are applied, 2-dimensional diffraction measurements are taken using the high-energy Synchrotron X-Rays and analyzed to provide high-resolution depth-resolved strain. This study will include fatigue comparisons through use of samples, which are both 'as-coated' as well as aged to various stages in a TBC lifespan. Studies reveal that variations in thermal gradients and mechanical loads create corresponding trends in depth resolved strains with the largest effects displayed at or near the bond coat/TBC interface. Single cycles as well as experiments targeting thermal gradient and mechanical effects were conducted to capture these trends. Inelastic behavior such as creep was observed and quantified for the different layers at high temperatures. From these studies more accurate lifespan predictions, material behaviors, and causes of failure modes can be determined. The work further develops measurement and analysis techniques for diffraction measurements in internal layers on a coated tubular sample which can be used by various industries to analyze similar geometries with different applications.
Show less - Date Issued
- 2014
- Identifier
- CFE0005640, ucf:50206
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005640
- Title
- Experimental Investigation of Advanced Ignition Systems for High Efficiency Combustion.
- Creator
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Almansour, Bader, Vasu Sumathi, Subith, Kapat, Jayanta, Kassab, Alain, Sarathy, S.Mani, University of Central Florida
- Abstract / Description
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Consumption of fossil and bio-derived fuels is growing due to energy demands associated with increase in population and standard of living across the globe. Power generation and transportation sectors are the primary two sources of fuel consumption, which have raised the demand for crude oil and led to serious environmental pollution issues. This demand for energy forced various government agencies to strengthen the allowable exhaust pollutant concentration limits. Recently, CO, CO2,...
Show moreConsumption of fossil and bio-derived fuels is growing due to energy demands associated with increase in population and standard of living across the globe. Power generation and transportation sectors are the primary two sources of fuel consumption, which have raised the demand for crude oil and led to serious environmental pollution issues. This demand for energy forced various government agencies to strengthen the allowable exhaust pollutant concentration limits. Recently, CO, CO2, particulate matter, and nitrogen oxides (NOx) emission restrictions have become more stringent to the extent that engines must operate at higher energy densities and efficiencies. Towards this goal, this doctoral study focused on evaluating advanced ignition systems and testing new biofuels for automotive combustion applications. First, a natural gas lean combustion mode was assessed by using advance ignition systems to provide higher brake power while maintaining the exhaust limits. A rigorous combustion data analysis was performed to identify the main reasons leading to improved performance in the case of prechamber equipped laser ignition. An overall efficiency improvement of 2.1% points was observed, compared to spark ignition, which in turn leads to save 633 PJ per year. In the second part of this dissertation, a spherical chamber was designed and validated to measure the laminar burning velocity (LBV) of a promising biofuel: 2,4-Dimethyl-3-pentanone, (DIPK), for homogenous charge compression ignition engines. LBV measurements were carried out with various diluent species (N2, Ar, and He) in order to provide several data points for development and validation of DIPK chemical kinetic mechanisms. It has been found that DIPK does not only have higher temperature and pressure sensitivities (compared to iso-octane), but additionally enabled a faster laminar burning velocity which leads to higher rate of heat release in reciprocating engines.
Show less - Date Issued
- 2018
- Identifier
- CFE0007387, ucf:52062
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007387
- Title
- Flutter Stability of Shrouded Turbomachinery Cascades with Nonlinear Frictional Damping.
- Creator
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Torkaman, Alex, Kauffman, Jeffrey L., Kapat, Jayanta, Raghavan, Seetha, Mackie, Kevin, University of Central Florida
- Abstract / Description
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Prediction of flutter in shrouded turbomachinery cascades is difficult due to i) coupling of aerodynamic drivers and structural dynamics of the cascade through shrouds, and ii) presence of nonlinear dry friction damping as a result of relative motion between adjacent shrouds. An analytical framework is developed in this dissertation to determine flutter stability of shrouded cascades with consideration of friction damping. This framework is an extension to the well-established energy method,...
Show morePrediction of flutter in shrouded turbomachinery cascades is difficult due to i) coupling of aerodynamic drivers and structural dynamics of the cascade through shrouds, and ii) presence of nonlinear dry friction damping as a result of relative motion between adjacent shrouds. An analytical framework is developed in this dissertation to determine flutter stability of shrouded cascades with consideration of friction damping. This framework is an extension to the well-established energy method, and it includes all contributing factors affecting stability of the cascade such as aerodynamic excitation and the stabilizing effects of dry friction damping caused by nonlinear contact forces between adjacent blades. This framework is developed to address a shortcoming in current analytical methods for flutter assessment in the industry. The influence of dry friction damping is typically not included due to complexity associated with nonlinearity, leading to uncertainty about exact threshold of flutter occurrence. The new analytical framework developed in this dissertation will increase the accuracy of flutter prediction method that is used for design and optimization of gas turbines.A hybrid time-frequency-time domain solution method is developed to solve aeroelastic equations of motion in both fluid and structural domains. Solution steps and their sequencing are optimized for computational efficiency with large scale realistic models and analytical accuracy in determining nonlinear friction force. Information exchange between different domains is used to couple aerodynamic and structural solutions together for a comprehensive and accurate analysis of shrouded cascade flutter problem in presence of nonlinear friction.Example application to a shrouded IGT blade shows that the influence of nonlinear friction damping in flutter suppression of an aerodynamically unstable cascade is significant. Comparison with engine test data shows that at observed vibration amplitudes in operation friction damping is sufficient to overcome aerodynamic excitation of this aerodynamically unstable cascade, resulting in overall cascade stability.
Show less - Date Issued
- 2018
- Identifier
- CFE0007379, ucf:52077
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007379
