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- Title
- A DYNAMIC MODEL OF THE HUMAN/COOLINGSYSTEM/CLOTHING/ENVIRONMENT SYSTEM.
- Creator
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pu, zhengxiang, Kapat, Jayanta, University of Central Florida
- Abstract / Description
-
The human body compensates well for moderate climatic heat stress, but artificial environments often block or overwhelm physiological defense mechanism. Personal protective equipment (PPE) is one of sources of heat stress. It protects individual from chemical, physical, or biological hazards, but the high thermal insulation and low vapor permeability of PPE may also lead to substantial heat stress. Personal cooling is widely used to alleviate heat stress, especially for those situations where...
Show moreThe human body compensates well for moderate climatic heat stress, but artificial environments often block or overwhelm physiological defense mechanism. Personal protective equipment (PPE) is one of sources of heat stress. It protects individual from chemical, physical, or biological hazards, but the high thermal insulation and low vapor permeability of PPE may also lead to substantial heat stress. Personal cooling is widely used to alleviate heat stress, especially for those situations where ambient environmental cooling is not economically viable or feasible. It is important to predict the physiological responses of a person wearing PPE with personal cooling to make sure that the individual is free of heat stress, as well as any additional discomfort that may occur. Air temperature, radiant temperature, humidity and air movement are the four basic environmental parameters that affect human response to thermal environments. Combined with the personal parameters of metabolic heat generated by human activity and clothing worn by a person, they provide the six fundamental factors which define human thermal environments. If personal cooling system is available, the fluid flow speed, cooling tube distribution density and fluid inlet temperature have significant effects on the human thermal comfort. It is impractical to evaluate the problem experimentally due to too many factors involved. A thermal model was developed to improve human body thermal comfort prediction. The system researched includes human body, personal cooling system, clothing and environment. An existing model of thermoregulation is taken as a starting point. Changes and additions are made to provide better prediction. Personal cooling model was developed and it includes liquid cooling model, air cooling model and ice cooling model. Thermal resistance networks for the cooling system are built up; additionally a combined model of heat and mass transfer from cooling garment through clothing to environment is developed and incorporated into the personal cooling model and thermoregulatory model. The control volume method is employed to carry out the numerical calculation. An example simulation is presented for extra-vehicular activities on Mars. The simulation results agree well with available experimental data, though a small discrepancy between simulation results and experimental data is observed during the beginning of the cooling process. Compared with a water cooling lumped model, the thermal model provides a much better prediction. For water cooling, parametric study shows that the cooling water inlet temperature and liner thermal resistance have great effects on the maximum exposure time; PPE resistance and cooling water flow rate do not have much impact on the maximum exposure time. For air cooling, cooling air flow rate, inlet temperature, relative humidity and liner resistance have great effects on the maximum exposure time.
Show less - Date Issued
- 2005
- Identifier
- CFE0000416, ucf:46407
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000416
- 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
- Adiabatic Film Cooling Effectiveness of a Transpiration-Cooled Leading Edge Fabricated by Laser Additive Manufacturing.
- Creator
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Calderon, Luisana, Kapat, Jayanta, Raghavan, Seetha, Mingareev, Ilya, University of Central Florida
- Abstract / Description
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Laser additive manufacturing (LAM) is an emerging technology capable of fabricating complex geometries not possibly made by investment casting methods for gas turbine applications. LAM techniques consist of building parts in a layer-by-layer process by selectively melting metal powders. In the present study, a mock leading edge segment of a turbine blade fabricated by LAM of Inconel 718 powders is investigated. For this particular design, the traditional showerhead film cooling holes have...
Show moreLaser additive manufacturing (LAM) is an emerging technology capable of fabricating complex geometries not possibly made by investment casting methods for gas turbine applications. LAM techniques consist of building parts in a layer-by-layer process by selectively melting metal powders. In the present study, a mock leading edge segment of a turbine blade fabricated by LAM of Inconel 718 powders is investigated. For this particular design, the traditional showerhead film cooling holes have been replaced by two strips containing engineered-porous regions with the purpose of simulating the effect of transpiration cooling. Transpiration cooling has been considered a promising external convective cooling method capable of providing a more uniform film and higher adiabatic film cooling effectiveness than conventional discrete film cooling. In addition, many studies have shown that this technique can yield high firing temperatures with much less coolant consumption than discrete film cooling. In this current study, adiabatic film cooling effectiveness is investigated by means of mass transfer using pressure sensitive paint (PSP). The experiments are conducted for blowing ratios ranging between M = 0.03 and M = 0.28 for a nominal density ratio of 1.5. The density ratio is obtained by using air as the mainstream flow and CO2 as the secondary flow (or coolant source). Results indicate higher coverage and film cooling effectiveness when increasing blowing ratio at the expense of higher pressure drop. In addition, the experimental results are compared to numerical analyses performed using steady state Reynolds Average Navier Stokes (RANS) simulations.
Show less - Date Issued
- 2018
- Identifier
- CFE0007315, ucf:52117
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007315
- Title
- Aerodynamic Characteristics of a Gas Turbine Exhaust Diffuser with an Accompanying Exhaust Collection System.
- Creator
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Bernier, Bryan, Kapat, Jayanta, Deng, Weiwei, Raghavan, Seetha, University of Central Florida
- Abstract / Description
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The effects of an industrial gas turbine's Exhaust Collector Box (ECB) geometry on static pressure recovery and total pressure loss were investigated in this study experimentally and computationally. This study aims to further understand how exit boundary conditions affect the performance of a diffuser system as well as the accuracy of industry standard computational models. A design of experiments approach was taken using a Box-Behnken design method for investigating three geometric...
Show moreThe effects of an industrial gas turbine's Exhaust Collector Box (ECB) geometry on static pressure recovery and total pressure loss were investigated in this study experimentally and computationally. This study aims to further understand how exit boundary conditions affect the performance of a diffuser system as well as the accuracy of industry standard computational models. A design of experiments approach was taken using a Box-Behnken design method for investigating three geometric parameters of the ECB. In this investigation, the exhaust diffuser remained constant through each test, with only the ECB being varied. A system performance analysis was conducted for each geometry using the total pressure loss and static pressure recovery from the diffuser inlet to the ECB exit. Velocity and total pressure profiles obtained with a hotwire anemometer and Kiel probe at the exit of the diffuser and at the exit of the ECB are also presented in this study. A total of 13 different ECB geometries are investigated at a Reynolds number of 60,000. Results obtained from these experimental tests are used to investigate the accuracy of a 3-dimensional RANS with realizable k-? turbulence model from the commercial software package Star-CCM+. The study confirms the existence of strong counter-rotating helical vortices within the ECB which significantly affect the flow within the diffuser. Evidence of a strong recirculation zone within the ECB was found to force separation within the exhaust diffuser which imposed a circumferentially asymmetric pressure field at the inlet of the diffuser. Increasing the ECB width proved to decrease the magnitude of this effect, increasing the diffuser protrusion reduced this effect to a lesser degree. The combined effect of increasing the ECB Length and Width increased the expansion area ratio, proving to increase the system pressure recovery by as much as 19% over the nominal case. Additionally, the realizable k-? turbulence model was able to accurately rank all 13 cases in order by performance; however the predicted magnitudes of the pressure recovery and total pressure loss were poor for the cases with strong vortices. For the large volume cases with weak vortices, the CFD was able to accurately represent the total pressure loss of the system within 5%.
Show less - Date Issued
- 2012
- Identifier
- CFE0004517, ucf:49296
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004517
- Title
- Aeroelastic Investigation of a Circumferentially Varying Tip Gap in an Axial Compressor Rotor.
- Creator
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Canon, Ornan, Kapat, Jayanta, Vasu Sumathi, Subith, Kauffman, Jeffrey, Mackie, Kevin, Kiesow, Hans-jurgen, University of Central Florida
- Abstract / Description
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The tip leakage flow in axial compressors is a significant factor in engine performance and a subject of investigation over the last several decades. Many studies have already shown that the vortices generated by this tip leakage can have a negative impact on the surrounding flow field and overall performance, and could potentially lead to excitations as well. This study examines the effect of these vortices on aeroelasticity. Specifically, it looks at the effect from a circumferentially...
Show moreThe tip leakage flow in axial compressors is a significant factor in engine performance and a subject of investigation over the last several decades. Many studies have already shown that the vortices generated by this tip leakage can have a negative impact on the surrounding flow field and overall performance, and could potentially lead to excitations as well. This study examines the effect of these vortices on aeroelasticity. Specifically, it looks at the effect from a circumferentially varying tip gap, such as that produced by casing ovalization.For this project, the casing ovalization of an industrial gas turbine compressor was modeled using a frequency domain solver, without the need for a full wheel model. Both the vibratory and aerodynamic calculations were conducted in order to assess the aeroelastic response of the blade, as well as the aerodynamic impact. Engine test data was implemented in order to model realistic levels of casing ovalization and to calibrate the analytical models. Comparisons to a well-established method are also conducted to further calibrate the models. The calculations showed that for the gap variations imposed, the instantaneous effects aligned with expectations. However, the variation from small and large gaps had a canceling effect on each other over the cycle of oscillation around the engine.
Show less - Date Issued
- 2016
- Identifier
- CFE0006682, ucf:51926
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006682
- Title
- AN EXPERIMENTAL AND NUMERICAL STUDY OF SECONDARY FLOWS AND FILM COOLING EFFECTIVENESS IN A TRANSONIC CASCADE.
- Creator
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Kullberg, James, Kapat, Jayanta, University of Central Florida
- Abstract / Description
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In the modern world, gas turbines are widely used in aircraft propulsion and electricity generation. These applications represent a massive use of energy worldwide, so even a very small increase in efficiency would have a significant beneficial economic and environmental impact. There are many ways to optimize the operation of a gas turbine, but a fundamental approach is to increase the turbine inlet temperature to increase the basic thermodynamic efficiency of the turbine. However, these...
Show moreIn the modern world, gas turbines are widely used in aircraft propulsion and electricity generation. These applications represent a massive use of energy worldwide, so even a very small increase in efficiency would have a significant beneficial economic and environmental impact. There are many ways to optimize the operation of a gas turbine, but a fundamental approach is to increase the turbine inlet temperature to increase the basic thermodynamic efficiency of the turbine. However, these temperatures are already well above the melting temperature of the components. A primary cooling methodology, called film cooling, creates a blanket of cool air over the surface and is an effective way to help protect these components from the hot mainstream gasses. This paper focuses on the effect of the film holes upstream of the first row of blades in the turbine because this is the section that experiences the highest thermal stresses. Many factors can determine the effectiveness of the film cooling, so a complete understanding can lead to effective results with the minimum flow rate of coolant air. Many studies have been published on the subject of film cooling, but because of the difficulty and expense of simulating turbine realistic conditions, many authors introduce vast simplifications such as low speed conditions or linear cascades. These simplifications do not adequately represent the behavior of a turbine and therefore their results are of limited use. This study attempts to eliminate many of those simplifications. The test rig used in this research is based on the NASA-GE E3 design, which stands for Energy Efficient Engine. It was introduced into the public domain to provide an advanced platform from which open-literature research could be performed. Experimental tests on a transonic annular rig are time-consuming and expensive, so it is desirable to use experimental results to validate a computational model which can then be used to extract much more information. The purpose of this work is to create a numerical model that can be used to simulate many different scenarios and then to apply these results to experimental data.
Show less - Date Issued
- 2011
- Identifier
- CFH0003772, ucf:44728
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0003772
- Title
- AN EXPERIMENTAL INVESTIGATION OF HEAT TRANSFER FOR ARRAYS OF IMPINGEMENT JETS ONTO THE FEATURED SURFACES WITH CYLINDRICAL AND ELLIPTICAL RAISED SURFACES.
- Creator
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Medina, Marc A, Kapat, Jayanta, University of Central Florida
- Abstract / Description
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This study focuses on multi-jet impingement for gas turbine geometries in which the objective is to understand the influence of the roughness elements on a target surface to the heat transfer. Current work has proven that implementing roughness elements for multi-jet impingement target surfaces has increased heat transfer ranging anywhere from 10-30%. This study has chosen to investigate three different roughness elements, elliptical in cross-section, to compare to smooth surface geometries...
Show moreThis study focuses on multi-jet impingement for gas turbine geometries in which the objective is to understand the influence of the roughness elements on a target surface to the heat transfer. Current work has proven that implementing roughness elements for multi-jet impingement target surfaces has increased heat transfer ranging anywhere from 10-30%. This study has chosen to investigate three different roughness elements, elliptical in cross-section, to compare to smooth surface geometries for multi-jet impingement. An experimental was taken for this study to extend the current knowledge of multi-jet impingement geometries and to further understand the heat transfer performance. A temperature sensitive paint (TSP) technique was used to measure the heat transfer on the target surface, in which the local temperature was measured to estimate area averaged heat transfer coefficient (HTC) and row averaged HTC. In order stay consistent with literature, non-dimensional parameters were used for geometry locations and boundaries. For this study, the Reynolds number range, based on jet diameter and mass flux, is 10-15k. The X/D (streamwise direction), Y/D (spanwise direction), Z/D (channel height direction), L/D (thickness of the jet plate) constraints for this study are 5, 6, 3, and 1 respectively. From the local heat transfer distributions of the different roughness elements, it is concluded that the inclusion of these elements increases heat transfer by 2-12% as compared to a flat/smooth target plate. It is therefore recommended from this study, that elements, elliptical in shape, provide favorability in heat transfer for gas turbine configurations.
Show less - Date Issued
- 2016
- Identifier
- CFH2000131, ucf:46021
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000131
- Title
- AN IMPROVED THERMOREGULATORY MODEL FOR COOLING GARMENT APPLICATIONS WITH TRANSIENT METABOLIC RATES.
- Creator
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Westin, Johan, Kapat, Jayanta, University of Central Florida
- Abstract / Description
-
Current state-of-the-art thermoregulatory models do not predict body temperatures with the accuracies that are required for the development of automatic cooling control in liquid cooling garment (LCG) systems. Automatic cooling control would be beneficial in a variety of space, aviation, military, and industrial environments for optimizing cooling efficiency, for making LCGs as portable and practical as possible, for alleviating the individual from manual cooling control, and for improving...
Show moreCurrent state-of-the-art thermoregulatory models do not predict body temperatures with the accuracies that are required for the development of automatic cooling control in liquid cooling garment (LCG) systems. Automatic cooling control would be beneficial in a variety of space, aviation, military, and industrial environments for optimizing cooling efficiency, for making LCGs as portable and practical as possible, for alleviating the individual from manual cooling control, and for improving thermal comfort and cognitive performance. In this study, we adopt the Fiala thermoregulatory model, which has previously demonstrated state-of-the-art predictive abilities in air environments, for use in LCG environments. We validate the numerical formulation with analytical solutions to the bioheat equation, and find our model to be accurate and stable with a variety of different grid configurations. We then compare the thermoregulatory model's tissue temperature predictions with experimental data where individuals, equipped with an LCG, exercise according to a 700 W rectangular type activity schedule. The root mean square (RMS) deviation between the model response and the mean experimental group response is 0.16°C for the rectal temperature and 0.70°C for the mean skin temperature, which is within state-of-the-art variations. However, with a mean absolute body heat storage error (e_BHS_mean) of 9.7 W·h, the model fails to satisfy the ±6.5 W·h accuracy that is required for the automatic LCG cooling control development. In order to improve model predictions, we modify the blood flow dynamics of the thermoregulatory model. Instead of using step responses to changing requirements, we introduce exponential responses to the muscle blood flow and the vasoconstriction command. We find that such modifications have an insignificant effect on temperature predictions. However, a new vasoconstriction dependency, i.e. the rate of change of hypothalamus temperature weighted by the hypothalamus error signal (DThy·dThy/dt), proves to be an important signal that governs the thermoregulatory response during conditions of simultaneously increasing core and decreasing skin temperatures, which is a common scenario in LCG environments. With the new DThy·dThy/dt dependency in the vasoconstriction command, the e_BHS_mean for the exercise period is reduced by 59% (from 12.9 W·h to 5.2 W·h). Even though the new e_BHS_mean of 5.8 W·h for the total activity schedule is within the target accuracy of ±6.5 W·h, e_BHS fails to stay within the target accuracy during the entire activity schedule. With additional improvements to the central blood pool formulation, the LCG boundary condition, and the agreement between model set-points and actual experimental initial conditions, it seems possible to achieve the strict accuracy that is needed for automatic cooling control development.
Show less - Date Issued
- 2008
- Identifier
- CFE0002460, ucf:47707
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002460
- Title
- AN UNCERTAINTY QUANTIFICATION OF THE VARIATION OF INTERNAL HEAT TRANSFER COEFFICIENTS AND THE EFFECT ON AIRFOIL LIFE.
- Creator
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Marsh, Jan, Kapat, Jayanta, University of Central Florida
- Abstract / Description
-
Uncertainty in accurately knowing applied internal heat transfer coefficients inside of a cooling passage can lead to variability in predicting low cycle fatigue life of a turbine vane or blade. Under-predicting a life value for a turbine part can have disastrous effects on the engine as a whole, and can negate efforts in innovative design for advanced cooling techniques for turbine components. Quantification of this fatigue life uncertainty utilizing a computational framework is the primary...
Show moreUncertainty in accurately knowing applied internal heat transfer coefficients inside of a cooling passage can lead to variability in predicting low cycle fatigue life of a turbine vane or blade. Under-predicting a life value for a turbine part can have disastrous effects on the engine as a whole, and can negate efforts in innovative design for advanced cooling techniques for turbine components. Quantification of this fatigue life uncertainty utilizing a computational framework is the primary objective of this thesis. Through the use of probabilistic design methodologies a process is developed to simulate uncertainties of internal heat transfer coefficient, which are then applied to the aft section of a non-rotating turbine blade component, internally cooled through a multi-pass serpentine channel. While keeping all other parameters constant internal heat transfer coefficients are varied according to a prescribed uncertainty range throughout the passages. The effect on the low cycle fatigue life of the airfoil is then evaluated at three discrete locations: near the base of the airfoil, towards the tip, and at mid-span. A generic low cycle fatigue life prediction model is used for these evaluations. Even though the probabilistic design process uses independent random numbers to simulate the variation, in reality, heat transfer coefficients at points located closely together should be correlated. For this reason, an autocorrelation function is implemented. By changing the value of this function the strength of the correlation of neighboring internal heat transfer coefficients to each other over a certain distance can be controlled. In order to test the effect that this correlation strength has on the low cycle fatigue life calculation, low and high values are chosen and analyzed. The magnitude of the prescribed uncertainty range of the internal heat transfer coefficient variation is varied to further study the effects on life. Investigated values include 5%, 10% and 20% for the straight ribbed passages and 10%, 20%, and 40% for both the tip and hub turns. As expected there is a significant dependence of low cycle fatigue life to the variation in internal heat transfer coefficients. For the 20/40% case, variations in life as high as 50-60% are recorded, furthermore a trend is observed showing that as the magnitude of the uncertainty range of internal heat transfer coefficients narrows so does the range of the low cycle fatigue life uncertainty.
Show less - Date Issued
- 2010
- Identifier
- CFE0003496, ucf:48975
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003496
- Title
- Analysis of Heat Transfer on Turbulence Generating Ribs using Dynamic Mode Decomposition.
- Creator
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Elmore, Michael, Kapat, Jayanta, Ahmed, Kareem, Bhattacharya, Samik, University of Central Florida
- Abstract / Description
-
Ducts with turbulence-promoting ribs are common in heat transfer applications. This study usesa recent modal extraction technique called Dynamic Mode Decomposition (DMD) to determinemode shapes of the spatially and temporally complex flowfield inside a ribbed duct. One subjectmissing from current literature is a method of directly linking a mode to a certain engineeringquantity of interest. Presented is a generalized methodology for producing such a link utilizing thedata from the DMD...
Show moreDucts with turbulence-promoting ribs are common in heat transfer applications. This study usesa recent modal extraction technique called Dynamic Mode Decomposition (DMD) to determinemode shapes of the spatially and temporally complex flowfield inside a ribbed duct. One subjectmissing from current literature is a method of directly linking a mode to a certain engineeringquantity of interest. Presented is a generalized methodology for producing such a link utilizing thedata from the DMD analysis. Theory suggests exciting the modes which are identified may causethe flow to change in such a way to promote the quantity of interest, in this case, heat transfer. Thistheory is tested by contouring the walls of the duct by the extracted mode shapes.The test procedure is taken from an industrial perspective. An initial, unmodified geometry pro-vides a baseline for comparison to later contoured models. The initial case is run as a steady-stateReynolds-Averaged Navier-Stokes model. Large-Eddy Simulation generates the necessary datafor the DMD analysis. Several mode shapes extracted from the flow are applied to the duct wallsand run again in the RANS model, then compared to the baseline, and their relative performanceexamined.
Show less - Date Issued
- 2018
- Identifier
- CFE0007328, ucf:52123
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007328
- Title
- Characterization of Acoustic Modes in Aeroengines.
- Creator
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Otero, Michelle, Ahmed, Kareem, Kapat, Jayanta, Bhattacharya, Samik, University of Central Florida
- Abstract / Description
-
Acoustic instabilities remain a key design concern faced in the development of liquid rocket engines. The interaction between the acoustic modes and the occurring combustion reactions can be detrimental to the engine. The fluctuating pressure waves resulting from the flame oscillations in the system can potentially lead to engine failure. For this reason, research in acoustic instabilities and methods to minimize the influences on the engine, has maintain interest in the aerospace community....
Show moreAcoustic instabilities remain a key design concern faced in the development of liquid rocket engines. The interaction between the acoustic modes and the occurring combustion reactions can be detrimental to the engine. The fluctuating pressure waves resulting from the flame oscillations in the system can potentially lead to engine failure. For this reason, research in acoustic instabilities and methods to minimize the influences on the engine, has maintain interest in the aerospace community. The scope of this study was to design, optimize and characterize acoustic behaviors of a scaled rocket combustion chamber simulating acoustic pressure waves. Tangential and longitudinal acoustic waves of the system were extracted and validated through analytical and computational fluids dynamics models. The results of this study will assist with the process of extracting dominant oscillation frequencies of a system essential in the design of acoustic suppression devices for attenuation of critical frequencies.
Show less - Date Issued
- 2018
- Identifier
- CFE0007354, ucf:52081
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007354
- Title
- CHARACTERIZATION OF AN INLINE ROW IMPINGEMENT CHANNEL FOR TURBINE BLADE COOLING APPLICATIONS.
- Creator
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Ricklick, Mark, Kapat, Jayanta, University of Central Florida
- Abstract / Description
-
Gas turbines have become an intricate part of today's society. Besides powering practically all 200,000+ passenger aircraft in use today, they are also a predominate form of power generation when coupled with a generator. The fact that they are highly efficient, and capable of large power to weight ratios, makes gas turbines an ideal solution for many power requirement issues faced today. Designers have even been able to develop small, micro-turbines capable of producing efficient...
Show moreGas turbines have become an intricate part of today's society. Besides powering practically all 200,000+ passenger aircraft in use today, they are also a predominate form of power generation when coupled with a generator. The fact that they are highly efficient, and capable of large power to weight ratios, makes gas turbines an ideal solution for many power requirement issues faced today. Designers have even been able to develop small, micro-turbines capable of producing efficient portable power. Part of the turbine's success is the fact that their efficiency levels have continuously risen since their introduction in the early 1800's. Along with improvements in our understanding and designs of the aerodynamic components of the turbine, as well as improvements in the areas of material design and combustion control, advances in component cooling techniques have predominantly contributed to this success. This is the result of a simple thermodynamic concept; as the turbine inlet temperature is increased, the overall efficiency of the machine increases as well. Designers have exploited this fact to the extent that modern gas turbines produce rotor inlet temperatures beyond the melting point of the sophisticated materials used within them. This has only been possible through the use of sophisticated cooling techniques, particularly in the 1st stage vanes and blades. Some of the cooling techniques employed today have been internal cooling channels enhanced with various features, film and showerhead cooling, as well as internal impingement cooling scenarios. Impingement cooling has proven to be one of the most capable heat removal processes, and the combination of this cooling feature with that of channel flow, as is done in impingement channel cooling, creates a scenario that has understandably received a great deal of attention in recent years. This study has investigated several of the unpublished characteristics of these impingement channels, including the channel height effects on the performance of the channel side walls, effects of bulk temperature increase on heat transfer coefficients, circumferential heat variation effects, and effects on the uniformity of the heat transfer distribution. The main objectives of this dissertation are to explore the various previously unstudied characteristics of impingement channels, in order to sufficiently predict their performance in a wide range of applications. The potential exists, therefore, for a designer to develop a blade with cooling characteristics specifically tailored to the expected component thermal loads. Temperature sensitive paint (TSP) is one of several non-intrusive optical temperature measurements techniques that have gained a significant amount of popularity in the last decade. By employing the use of TSP, we have the ability to provide very accurate (less than 1 degree Celsius uncertainty), high resolution full-field temperature measurements. This has allowed us to investigate the local heat transfer characteristics of the various channel surfaces under a variety of steady state testing conditions. The comparison of thermal performance and uniformity for each impingement channel configuration then highlights the benefits and disadvantages of various configurations. Through these investigations, it has been shown that the channel side walls provide heat transfer coefficients comparable to those found on the target surface, especially at small impingement heights. Although the side walls suffer from highly non-uniform performance near the start of the channel, the profiles become very uniform as the cross flow develops and becomes a dominating contributor to the heat transfer coefficient. Increases in channel height result in increased non-uniformity in the streamwise direction and decreased heat transfer levels. Bulk temperature increases have also been shown to be an important consideration when investigating surfaces dominated by cross flow heat transfer effects, as enhancements up to 80% in some areas may be computed. Considerations of these bulk temperature changes also allow the determination of the point at which the flow transitions from an impingement dominated regime to one that is dominated by cross flow effects. Finally, circumferential heat variations have proven to have negligible effects on the calculated heat transfer coefficient, with the observed differences in heat transfer coefficient being contributed to the unaccounted variations in channel bulk temperature.
Show less - Date Issued
- 2009
- Identifier
- CFE0002955, ucf:47948
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002955
- 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
-
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
- Characterization of SLM-Manufactured Turbine Blade Microfeatures from Superalloy Powders.
- Creator
-
Ealy, Brandon, Kapat, Jayanta, Ahmed, Kareem, Vasu Sumathi, Subith, University of Central Florida
- Abstract / Description
-
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
- Combustion Instability Mechanism of a Reacting Jet in Cross Flow at Gas Turbine Operating Conditions.
- Creator
-
Pent, Jared, Kapat, Jayanta, Deng, Weiwei, Gordon, Ali, Vasu Sumathi, Subith, Martin, Scott, University of Central Florida
- Abstract / Description
-
Modern gas turbine designs often include lean premixed combustion for its emissions benefits; however, this type of combustion process is susceptible to self-excited combustion instabilities that can lead to damaging heat loads and system vibrations. This study focuses on identifying a mechanism of combustion instability of a reacting jet in cross flow, a flow feature that is widely used in the design of gas turbine combustion systems. Experimental results from a related study are used to...
Show moreModern gas turbine designs often include lean premixed combustion for its emissions benefits; however, this type of combustion process is susceptible to self-excited combustion instabilities that can lead to damaging heat loads and system vibrations. This study focuses on identifying a mechanism of combustion instability of a reacting jet in cross flow, a flow feature that is widely used in the design of gas turbine combustion systems. Experimental results from a related study are used to validate and complement three numerical tools that are applied in this study (-) self-excited Large Eddy Simulations, 3D thermoacoustic modeling, and 1D instability modeling. Based on the experimental and numerical results, a mechanism was identified that included a contribution from the jet in cross flow impedance as well as an overall jet flame time lag. The jet impedance is simply a function of the acoustic properties of the geometry while the flame time lag can be separated into jet velocity, equivalence ratio, and strain fluctuations, depending on the operating conditions and setup. For the specific application investigated in this study, it was found that the jet velocity and equivalence ratio fluctuations are important, however, the effect of the strain fluctuations on the heat release are minimal due to the high operating pressure. A mathematical heat release model was derived based on the proposed mechanism and implemented into a 3D thermoacoustic tool as well as a 1D instability tool. A three-point stability trend observed in the experimental data was correctly captured by the 3D thermoacoustic tool using the derived heat release model. Stability maps were generated with the 1D instability tool to demonstrate regions of stable operation that can be achieved as a function of the proposed mechanism parameters. The relative effect of the reacting jet in cross flow on the two dominant unstable modes was correctly captured in the stability maps. While additional mechanisms for a reacting jet in cross flow are possible at differing flow conditions, the mechanism proposed in this study was shown to correctly replicate the stability trends observed in the experimental tests and provides a fundamental understanding that can be applied for combustion system design.
Show less - Date Issued
- 2014
- Identifier
- CFE0005687, ucf:50154
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005687
- Title
- Combustion kinetics of advanced biofuels.
- Creator
-
Barari, Ghazal, Vasu Sumathi, Subith, Kapat, Jayanta, Kassab, Alain, Masunov, Artem, University of Central Florida
- Abstract / Description
-
Use of biofuels, especially in automotive applications, is a growing trend due to their potential to lower greenhouse gas emissions from combustion. Ketones are a class of biofuel candidates which are produced from cellulose. However, ketones received rather scarce attention from the combustion community compared to other classes such as, alcohols, esters, and ethers. There is little knowledge on their combustion performance and pollutant generation. Hence their combustion chemistry needs to...
Show moreUse of biofuels, especially in automotive applications, is a growing trend due to their potential to lower greenhouse gas emissions from combustion. Ketones are a class of biofuel candidates which are produced from cellulose. However, ketones received rather scarce attention from the combustion community compared to other classes such as, alcohols, esters, and ethers. There is little knowledge on their combustion performance and pollutant generation. Hence their combustion chemistry needs to be investigated in detail. Diisopropyl ketone (DIPK) is a promising biofuel candidate, which is produced using endophytic fungal conversion. A detailed understanding of the combustion kinetics of the oxidation of DIPK in advanced engines such as, the homogeneous charge compression ignition (HCCI) engine is warranted. This dissertation concentrates on the combustion kinetics of DIPK over a wide range of temperature and pressure with a focus on HCCI engine application.An existing DIPK kinetic mechanism has been reviewed and a single zone HCCI engine model has been modeled and validated against recent experimental data from Sandia National Lab. Therefore different HCCI modeling assumptions were tested and the DIPK reaction mechanism was modified with missing reactions and the required thermochemical data. As a result, the HCCI pressure trace, heat release rate and reactivity have been improved. In order to improve the ignition delay time simulation results, the low temperature oxidation of DIPK was studied as the fuel chemistry effects on the autoignition behavior becomes important in low temperature. Therefore DIPK low temperature oxidation experimental data was obtained from the synchrotron photoionization experiments conducted at the Advanced Light Source (ALS) so that the primary products as well as the dominant oxidation pathways are identified. Furthermore, the aldehydes oxidation, as a result of partial or incomplete combustion and as the primary stable intermediate products in oxidation and pyrolysis of biofuel were studied at low temperature in ALS. A high temperature reaction mechanism was created using the reaction class approach. The reaction mechanism for DIPK was improved using the experimental data along with quantum chemical calculation of activation energies and barriers as well as vibrational modes for the important reactions identified in ALS experiment. The rate constants for important reactions were calculated based on modified Arrhenius equation. DIPK oxidation and pyrolysis were studied at high temperature and pressure using UCF shock tube. The ignition delay times as well as the product (methane) time histories were investigated and used as validation targets for the new model.
Show less - Date Issued
- 2015
- Identifier
- CFE0005921, ucf:50847
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005921
- Title
- Comparison of Modeling Methods for Power Cycle Components Using Supercritical Carbon Dioxide as the Operating Fluid.
- Creator
-
Schmitt, Joshua, Kapat, Jayanta, Kassab, Alain, Vasu Sumathi, Subith, University of Central Florida
- Abstract / Description
-
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
- Compressibility Effect on Turbulent Flames and Detonation Initiation and Propagation.
- Creator
-
Sosa, Jonathan, Ahmed, Kareem, Kassab, Alain, Kapat, Jayanta, University of Central Florida
- Abstract / Description
-
This work presents the first measurement of turbulent burning velocities of a highly-turbulent compressible standing flame induced by shock-driven turbulence in a Turbulent Shock Tube. High-speed schlieren, chemiluminescence, PIV, and dynamic pressure measurements are made to quantify flame-turbulence interaction for high levels of turbulence at elevated temperatures and pressure. Distributions of turbulent velocities, vorticity and turbulent strain are provided for regions ahead and behind...
Show moreThis work presents the first measurement of turbulent burning velocities of a highly-turbulent compressible standing flame induced by shock-driven turbulence in a Turbulent Shock Tube. High-speed schlieren, chemiluminescence, PIV, and dynamic pressure measurements are made to quantify flame-turbulence interaction for high levels of turbulence at elevated temperatures and pressure. Distributions of turbulent velocities, vorticity and turbulent strain are provided for regions ahead and behind the standing flame. The turbulent flame speed is directly measured for the high-Mach standing turbulent flame. From measurements of the flame turbulent speed and turbulent Mach number, transition into a non-linear compressibility regime at turbulent Mach numbers above 0.4 is confirmed, and a possible mechanism for flame generated turbulence and deflagration-to-detonation transition is established.Additionally, this study presents the exploration of detonation wave propagation dynamics in premixed supersonic flows using a novel rotating detonation engine (RDE) configuration. An RDE with a coupled linear extension, referred to as ?DE, is used to divide detonations traveling radially in the RDE into linearly propagating waves. A tangential propagating wave is directed down a modular tangential linearized extension to the engine for ease of optical diagnostics and hardware configuration investigations. A premixed Mach 2 supersonic linear extension is coupled to the ?DE to investigate the effects of varying crossflow configurations for detonation propagation, particularly the interaction between detonations and supersonic reactive mixtures. Detonation waves are generated at the steady operating frequency of the RDE and visualized using high speed schlieren and broadband OH* chemiluminescence imaging. The stagnation pressure was varied from over- to ideally-expanded supersonic regimes. Experimental analysis of detonation interaction with the supersonic regimes show that the detonation propagates freely in the ideally-expanded regime. Deflagration-to-detonation transition (DDT) occurs in the over-expanded regime. Based on the data collected, the DDT process favors supersonic flow with higher source pressures. Lastly, this work presents the experimental evidence of controlled detonation wave initiation and propagation in hydrogen-air premixed hypersonic Mach 5 flows. A Mach 5 high-enthalpy facility is used to provide the premixed hydrogen-air stream targeted to match the boundary conditions (Chapman-Jouguet, CJ) for stable detonations. The work shows for the first-time flame deflagration-to-detonation transition through coupled mechanism of turbulent flame acceleration and shock-focusing in a premixed Mach 5 flow. The paper defines three new distinct regimes in a Mach 5 premixed flow: Deflagration-to-Detonation Transition (DDT), Unsteady Compressible Turbulent Flames, and Shock-Induced Combustion. With rising national interest in hypersonics and reduced combustion emissions, the discovery and classification of these new combustion regimes allows for a possible pathway to develop and integrate detonation technology enabling hypersonic propulsion technology and advanced power systems.
Show less - Date Issued
- 2019
- Identifier
- CFE0007534, ucf:52607
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007534
- Title
- Compressible Turbulent Flame Speed of Highly Turbulent Standing Flames.
- Creator
-
Sosa, Jonathan, Ahmed, Kareem, Kassab, Alain, Kapat, Jayanta, University of Central Florida
- Abstract / Description
-
This work presents the first measurement of turbulent burning velocities of a highly-turbulent compressible standing flame induced by shock-driven turbulence in a Turbulent Shock Tube. High-speed schlieren, chemiluminescence, PIV, and dynamic pressure measurements are made to quantify flame-turbulence interaction for high levels of turbulence at elevated temperatures and pressure. Distributions of turbulent velocities, vorticity and turbulent strain are provided for regions ahead and behind...
Show moreThis work presents the first measurement of turbulent burning velocities of a highly-turbulent compressible standing flame induced by shock-driven turbulence in a Turbulent Shock Tube. High-speed schlieren, chemiluminescence, PIV, and dynamic pressure measurements are made to quantify flame-turbulence interaction for high levels of turbulence at elevated temperatures and pressure. Distributions of turbulent velocities, vorticity and turbulent strain are provided for regions ahead and behind the standing flame. The turbulent flame speed is directly measured for the high-Mach standing turbulent flame. From measurements of the flame turbulent speed and turbulent Mach number, transition into a non-linear compressibility regime at turbulent Mach numbers above 0.4 is confirmed, and a possible mechanism for flame generated turbulence and deflagration-to-detonation transition is established.
Show less - Date Issued
- 2018
- Identifier
- CFE0007102, ucf:51955
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007102
- Title
- CONJUGATE HEAT TRANSFER ANALYSIS OF COMBINED REGENERATIVE AND DISCRETE FILM COOLING IN A ROCKET NOZZLE.
- Creator
-
Pearce, Charlotte M, Kapat, Jayanta, University of Central Florida
- Abstract / Description
-
Conjugate heat transfer analysis has been carried out on an 89kN thrust chamber in order to evaluate whether combined discrete film cooling and regenerative cooling in a rocket nozzle is feasible. Several cooling configurations were tested against a baseline design of regenerative cooling only. New designs include combined cooling channels with one row of discrete film cooling holes near the throat of the nozzle, and turbulated cooling channels combined with a row of discrete film cooling...
Show moreConjugate heat transfer analysis has been carried out on an 89kN thrust chamber in order to evaluate whether combined discrete film cooling and regenerative cooling in a rocket nozzle is feasible. Several cooling configurations were tested against a baseline design of regenerative cooling only. New designs include combined cooling channels with one row of discrete film cooling holes near the throat of the nozzle, and turbulated cooling channels combined with a row of discrete film cooling holes. Blowing ratio and channel mass flow rate were both varied for each design. The effectiveness of each configuration was measured via the maximum hot gas-side nozzle wall temperature, which can be correlated to number of cycles to failure. A target maximum temperature of 613K was chosen. Combined film and regenerative cooling, when compared to the baseline regenerative cooling, reduced the hot gas side wall temperature from 667K to 638K. After adding turbulators to the cooling channels, combined film and regenerative cooling reduced the temperature to 592K. Analysis shows that combined regenerative and film cooling is feasible with significant consequences, however further improvements are possible with the use of turbulators in the regenerative cooling channels.
Show less - Date Issued
- 2016
- Identifier
- CFH2000138, ucf:45923
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000138