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- Title
- EFFECT OF PRESSURE GRADIENT AND WAKE ON ENDWALL FILM COOLING EFFECTIVENESS.
- Creator
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Rodriguez, Sylvette, Kapat, Jayanta, University of Central Florida
- Abstract / Description
-
Endwall film cooling is a necessity in modern gas turbines for safe and reliable operation. Performance of endwall film cooling is strongly influenced by the hot gas flow field, among other factors. For example, aerodynamic design determines secondary flow vortices such as passage vortices and corner vortices in the endwall region. Moreover blockage presented by the leading edge of the airfoil subjects the incoming flow to a stagnating pressure gradient leading to roll-up of the approaching...
Show moreEndwall film cooling is a necessity in modern gas turbines for safe and reliable operation. Performance of endwall film cooling is strongly influenced by the hot gas flow field, among other factors. For example, aerodynamic design determines secondary flow vortices such as passage vortices and corner vortices in the endwall region. Moreover blockage presented by the leading edge of the airfoil subjects the incoming flow to a stagnating pressure gradient leading to roll-up of the approaching boundary layer and horseshoe vortices. In addition, for a number of heavy frame power generation gas turbines that use cannular combustors, the hot and turbulent gases exiting from the combustor are delivered to the first stage vane through transition ducts. Wakes induced by walls separating adjacent transition ducts located upstream of first row vanes also influence the entering main gas flow field. Furthermore, as hot gas enters vane passages, it accelerates around the vane airfoils. This flow acceleration causes significant streamline curvature and impacts lateral spreading endwall coolant films. Thus endwall flow field, especially those in utility gas turbines with cannular combustors, is quite complicated in the presence of vortices, wakes and strong favorable pressure gradient with resulting flow acceleration. These flow features can seriously impact film cooling performance and make difficult the prediction of film cooling in endwall. This study investigates endwall film cooling under the influence of pressure gradient effects due to stagnation region of an axisymmetric airfoil and in mainstream favorable pressure gradient. It also investigates the impact of wake on endwall film cooling near the stagnation region of an airfoil. The investigation consists of experimental testing and numerical simulation. Endwall film cooling effectiveness is investigated near the stagnation region on an airfoil by placing an axisymmetric airfoil downstream of a single row of inclined cylindrical holes. The holes are inclined at 35° with a length-to-diameter ratio of 7.5 and pitch-to-diameter ratio of 3. The ratio of leading edge radius to hole diameter and the ratio of maximum airfoil thickness to hole diameter are 6 and 20 respectively. The distance of the leading edge of the airfoil is varied along the streamwise direction to simulate the different film cooling rows preceding the leading edge of the airfoil. Wake effects are induced by placing a rectangular plate upstream of the injection point where the ratio of plate thickness to hole diameter is 6.4, and its distance is also varied to investigate the impact of strong and mild wake on endwall film cooling effectiveness. Blowing ratio ranged from 0.5 to 1.5. Film cooling effectiveness is also investigated under the presence of mainstream pressure gradient with converging main flow streamlines. The streamwise pressure distribution is attained by placing side inserts into the mainstream. The results are presented for five holes of staggered inclined cylindrical holes. The inclination angle is 30° and the tests were conducted at two Reynolds number, 5000 and 8000. Numerical analysis is employed to aid the understanding of the mainstream and coolant flow interaction. The solution of the computational domain is performed using FLUENT software package from Fluent, Inc. The use of second order schemes were used in this study to provide the highest accuracy available. This study employed the Realizable κ-ε model with enhance wall treatment for all its cases. Endwall temperature distribution is measured using Temperature Sensitive Paint (TSP) technique and film cooling effectiveness is calculated from the measurements and compared against numerical predictions. Results show that the characteristics of average film effectiveness near the stagnation region do not change drastically. However, as the blowing ratio is increased jet to jet interaction is enhanced due to higher jet spreading resulting in higher jet coverage. In the presence of wake, mixing of the jet with the mainstream is enhanced particularly for low M. The velocity deficit created by the wake forms a pair of vortices offset from the wake centerline. These vortices lift the jet off the wall promoting the interaction of the jet with the mainstream resulting in a lower effectiveness. The jet interaction with the mainstream causes the jet to lose its cooling capabilities more rapidly which leads to a more sudden decay in film effectiveness. When film is discharged into accelerating main flow with converging streamlines, row-to-row coolant flow rate is not uniform leading to varying blowing ratios and cooling performance. Jet to jet interaction is reduced and jet lift off is observed for rows with high blowing ratio resulting in lower effectiveness.
Show less - Date Issued
- 2008
- Identifier
- CFE0002425, ucf:47769
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002425
- Title
- INTERACTION BETWEEN SECONDARY FLOW AND FILM COOLING JETS OF A REALISTIC ANNULAR AIRFOIL CASCADE (HIGH MACH NUMBER).
- Creator
-
Nguyen, Cuong, Kapat, Jayanta, University of Central Florida
- Abstract / Description
-
Film cooling is investigated on a flat plate both numerically and experimentally. Conical shaped film hole are investigated extensively and contribute to the current literature data, which is extremely rare in the open public domain. Both configuration of the cylindrical film holes, with and without a trench, are investigated in detail. Design of experiment technique was performed to find an optimum combination of both geometrical and fluid parameters to achieve the best film cooling...
Show moreFilm cooling is investigated on a flat plate both numerically and experimentally. Conical shaped film hole are investigated extensively and contribute to the current literature data, which is extremely rare in the open public domain. Both configuration of the cylindrical film holes, with and without a trench, are investigated in detail. Design of experiment technique was performed to find an optimum combination of both geometrical and fluid parameters to achieve the best film cooling performance. From this part of the study, it shows that film cooling performance can be enhanced up to 250% with the trenched film cooling versus non-trenched case provided the same amount of coolant. Since most of the relevant open literature is about film cooling on flat plate endwall cascade with linear extrusion airfoil, the purpose of the second part of this study is to examine the interaction of the secondary flow inside a 3D cascade and the injected film cooling jets. This is employed on the first stage of the aircraft gas turbine engine to protect the curvilinear (annular) endwall platform. The current study investigates the interaction between injected film jets and the secondary flow both experimentally and numerically at high Mach number (M=0.7). Validation shows good agreement between obtained data with the open literature. In general, it can be concluded that with an appropriate film coolant to mainstream blowing ratio, one can not only achieve the best film cooling effectiveness (FCE or η) on the downstream endwall but also maintain almost the same aerodynamic loss as in the un-cooled baseline case. Film performance acts nonlinearly with respect to blowing ratios as with film cooling on flat plate, in the other hand, with a right blowing ratio, film cooling performance is not affect much by secondary flow. In turn, film cooling jets do not increase pressure loss at the downstream wake area of the blades.
Show less - Date Issued
- 2010
- Identifier
- CFE0003546, ucf:48944
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003546
- 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
- FILM COOLING WITH WAKE PASSING APPLIED TO AN ANNULAR ENDWALL.
- Creator
-
Tran, Nghia, Kapat, Jayanta, University of Central Florida
- Abstract / Description
-
Advancement in turbine technology has far reaching effects on today's society and environment. With more than 90% of electricity and 100% of commercial air transport being produced by the usage of gas turbine, any advancement in turbine technology can have an impact on fuel used, pollutants and carbon dioxide emitted to the environment. Within the turbine engine, fully understanding film cooling is critical to reliability of a turbine engine. Film cooling is an efficient way to protect...
Show moreAdvancement in turbine technology has far reaching effects on today's society and environment. With more than 90% of electricity and 100% of commercial air transport being produced by the usage of gas turbine, any advancement in turbine technology can have an impact on fuel used, pollutants and carbon dioxide emitted to the environment. Within the turbine engine, fully understanding film cooling is critical to reliability of a turbine engine. Film cooling is an efficient way to protect the engine surface from the extremely hot incoming gas, which is at a temperature much higher than allowable temperature of even the most advanced super alloy used in turbine. Film cooling performance is affected by many factors: geometrical factors and as well as flow conditions. In most of the film cooling literature, film effectiveness has been used as criterion to judge and/or compare between film cooling designs. Film uniformity is also a critical factor, since it determines how well the coolant spread out downstream to protect the hot-gas-path surface of a gas turbine engine. Even after consideration of all geometrical factors and flow conditions, the film effectiveness is still affected by the stator-rotor interaction, in particular by the moving wakes produced by upstream airfoils. A complete analysis of end wall film cooling inside turbine is required to fully understand the phenomena. This full analysis is almost impossible in the academic arena. Therefore, a simplified but critical experimental rig and computational fluid model were designed to capture the effect of wake on film cooling inside an annular test section. The moving wakes are created by rotating a wheel with 12 spokes or rods with a variable speed motor. Thus changing the motor speed will alter the wake passing frequency. This design is an advancement over most previous studies in rectangular duct, which cannot simulate wakes in an annular passage as in an engine. This rig also includes film injection that allows study of impact of moving wakes on film cooling. This wake is a simplified representation of the trailing edge created by an upstream airfoil. An annulus with 30ð pitch test section is considered in this study. This experimental rig is based on an existing flat plate film cooling (BFC) rig that has been validated in the past. Measurement of velocity profiles within the moving wake downstream from the wake generator is used to validate the CFD rotating wake model. The open literature on film cooling and past experiments performed in the laboratory validated the CFD film cooling model. With these validations completed, the full CFD model predicts the wake and film cooling interaction. Nine CFD cases were considered by varying the film cooling blowing ratio and the wake Strouhal number. The results indicated that wakes highly enhance film cooling effectiveness near film cooling holes and degrades the film blanket downstream of the film injection, at the moment of wake passing. However, the time-averaged film cooling effectiveness is more or less the same with or without wake.
Show less - Date Issued
- 2010
- Identifier
- CFE0003483, ucf:48956
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003483
- Title
- THE EFFECT OF HEAT TRANSFER COEFFICIENT ON HIGH ASPECT RATIO CHANNEL ACCOMPANIED BY VARYING RIB ASPECT RATIO.
- Creator
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Le, An, Kapat, Jayanta, University of Central Florida
- Abstract / Description
-
Heat transfer and pressure data were performed and reported on two different rigs. The first rig has an aspect ratio of (19:1) with two different inlet conditions and the second rig is composed of two different aspect ratio channels, (1:8) and (1:4). Rib turbulators were used as a flow disruptor scheme to enhance the heat transfer and friction factor. Rib aspect ratios ranging from (1:1) to (1:5) rib-height-to-width ratio were used. The first channel rib-width-to-pitch (Wr/P) ratio was kept...
Show moreHeat transfer and pressure data were performed and reported on two different rigs. The first rig has an aspect ratio of (19:1) with two different inlet conditions and the second rig is composed of two different aspect ratio channels, (1:8) and (1:4). Rib turbulators were used as a flow disruptor scheme to enhance the heat transfer and friction factor. Rib aspect ratios ranging from (1:1) to (1:5) rib-height-to-width ratio were used. The first channel rib-width-to-pitch (Wr/P) ratio was kept at 1/2 where flow was kept at relatively low Reynolds numbers, between 3000 and 13000. Results from the current tests showed that existing correlations could be used for high aspect ratio channels in predicting the effectiveness of the cooling scheme. Two different inlet conditions were tested; one was arranged so that the flow was hydrodynamically fully-developed at the entrance of the heated section, while the other uses an abrupt entrance from bleeding off mass flow from a horizontal channel. The heat transfer augmentation (compared to a well known and accepted correlation proposed by Dittus-Boelter) in these channels are extremely high with an average of 350% to 400%. However, this was accompanied by a substantial increase in the pressure drop, causing the overall thermal performance to increase between twenty to thirty percent. The second channel rib-width-to-pitch ratio (Wr/P) ranges from 0.1, 0.3, and 0.5; the flow conditions are tested from 20,000 to 40,000 Reynolds number. Correlations for heat transfer and friction augmentation of the test data was also given. The test shows large rib blockage ratio does not demonstrate the best thermal performance; however it does give a high heat transfer augmentation ranging from 200 to 300 percent for both aspect ratios depending on the width of the used ribs.
Show less - Date Issued
- 2009
- Identifier
- CFE0002782, ucf:48130
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002782
- Title
- HEAT TRANSFER AUGMENTATION IN A NARROW RECTANGULAR DUCT WITH DIMPLES APPLIED TO A SINGLE WALL.
- Creator
-
Slabaugh, Carson, Kapat, Jayanta, University of Central Florida
- Abstract / Description
-
Establishing a clean and renewable energy supply is the preeminent engineering challenge of our time. Turbines, in some form, are responsible for more than 98 percent of all electricity generated in the United State and 100 percent of commercial and military air transport. The operation of these engines is clearly responsible for significant consumption of hydrocarbon fuels and, in turn, emission of green house gases into the atmosphere. With such wide-scale implementation, it is understood...
Show moreEstablishing a clean and renewable energy supply is the preeminent engineering challenge of our time. Turbines, in some form, are responsible for more than 98 percent of all electricity generated in the United State and 100 percent of commercial and military air transport. The operation of these engines is clearly responsible for significant consumption of hydrocarbon fuels and, in turn, emission of green house gases into the atmosphere. With such wide-scale implementation, it is understood that even the smallest increase in the operating efficiency of these machines can lead to enormous improvements over the current energy situation. These effects can extend from a reduction in the emission of greenhouse gases to lessening the nationÃÂ's dependence of foreign energy sources to lower energy prices for the consumer. The prominent means of increasing engine efficiency is by raising the ÃÂ'Turbine Inlet TemperatureÃÂ' ÃÂ the temperature of the mainstream flow after combustion, entering the first stage of the turbine section. The challenge is presented when these temperatures are forced beyond the allowable limits of the materials inside the machine. In order to protect these components, active cooling and protection methods are employed. The focus of this work is the development of more efficient means of cooling ÃÂ'hotÃÂ' turbine components. In doing so, the goal is to maximize the amount of heat removed by the coolant while minimizing the coolant mass flow rate: by removing a greater amount of heat with a lower coolant mass flow rate, more compressed air is left in the mainstream gas flow for combustion and power generation. This study is an investigation of the heat transfer augmentation through the fully-developed portion of a narrow rectangular duct (AR=2) characterized by the application of dimples to the bottom wall of the channel. Experimental testing and numerical modeling is performed for full support and validation of presented findings. The geometries are studied at channel Reynolds numbers of 20000, 30000, and 40000. The purpose is to understand the contribution of dimple geometries in the formation of flow structures that improve the advection of heat away from the channel walls. Experimental data reported includes the local and Nusselt number augmentation of the channel walls and the overall friction augmentation throughout the length of the duct. Computational results validate local Nusselt number results from experiments, in addition to providing further insight to local flow physics causing the observed surface phenomena. By contributing to a clearer understanding of the effects produced by these geometries, the development of more effective channel-cooling designs can be achieved.
Show less - Date Issued
- 2010
- Identifier
- CFE0003223, ucf:48511
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003223
- Title
- Characterization of Acoustic Modes in Aeroengines.
- Creator
-
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
- 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
- Investigation of Heat Transfer Enhancement Within a Concentric Annulus.
- Creator
-
Hanhold, Alexander, Kapat, Jayanta, Ahmed, Kareem, Vasu Sumathi, Subith, University of Central Florida
- Abstract / Description
-
Effective heat exchange is key for many energy applications including heat exchangers, heat extraction from heat source, and heat rejection to ambient thermal sink. This study focuses on the investigation for a specific heat exchange configuration, namely heat removal within a concentric annular passage using helical turbulators and jet impingement. Numerical testing was used to see how the different geometric parameters affect the heat transfer and pressure drop within the annulus by using...
Show moreEffective heat exchange is key for many energy applications including heat exchangers, heat extraction from heat source, and heat rejection to ambient thermal sink. This study focuses on the investigation for a specific heat exchange configuration, namely heat removal within a concentric annular passage using helical turbulators and jet impingement. Numerical testing was used to see how the different geometric parameters affect the heat transfer and pressure drop within the annulus by using helicoil turbulators. A vast range of designs were studied by changing the turbulator shape, pitch, and blockage ratio while maintaining a constant Reynolds number of 25,000. CFD was performed in STARCCM+ using the realizable ?-? turbulence model. Results show that turbulence and heat transfer increase with a higher blockage ratio and smaller pitch but the pressure drop is subsequently increased as well. The square turbulator promoted higher heat transfer compared to the circle turbulator but the pressure drop was significantly increased when the helix angle was greater than 20(&)deg; and blockage ratio greater than 0.48.Experimental and numerical efforts were used to find the heat transfer due to impingement jets on the target surface. Multiple flows as a function of jet Reynolds number ranging from 16,000-33,000 were tested for two geometries. Temperature Sensitive Paint (TSP) was utilized to observe local heat transfer. It was observed that jet degradation occurs after the 6th row of stream-wise impingement jets for both cases experimentally and it was difficult to numerically capture the effect of the cross flow from previous jets but managed to follow the same trend. The numerical results showed that they can be used with good agreement to predict the surface averaged Nusselt number to be within the 12% uncertainty found from experimental efforts. Geometry B was determined to perform better in terms of heat transfer as opposed to Geometry A with the same pressure loss.
Show less - Date Issued
- 2017
- Identifier
- CFE0007286, ucf:52155
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007286
- Title
- Detailed Understanding of Flow, Heat Transfer, and Pressure Drop Behavior in a Square Channel With 45 Deg Ribs.
- Creator
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Ahmed, Lumaya, Kapat, Jayanta, Gordon, Ali, Ahmed, Kareem, Shivamoggi, Bhimsen, University of Central Florida
- Abstract / Description
-
Internal Duct Cooling (IDC) with rib turbulators is one of the common cooling techniques applied inside the turbine airfoils. It is very important for the gas turbine industry to design and develop an optimized cooling channel that maximizes the amount of heat removed, while simultaneously minimizing the pressure drop for a target overall cooling effectiveness. Angled ribs perform superior to the transverse ribs due to additional secondary flow associated with them. However, they result in a...
Show moreInternal Duct Cooling (IDC) with rib turbulators is one of the common cooling techniques applied inside the turbine airfoils. It is very important for the gas turbine industry to design and develop an optimized cooling channel that maximizes the amount of heat removed, while simultaneously minimizing the pressure drop for a target overall cooling effectiveness. Angled ribs perform superior to the transverse ribs due to additional secondary flow associated with them. However, they result in a highly non-homogenous heat transfer distribution, which is a manifestation of the complex, turbulent flow field inside the channel. It is very important to comprehend the secondary flow physics to characterize the heat transfer distribution in such angled ribbed channels. Additionally, due to the manufacturing constraint, the gas turbine industry encounters a challenge to make ribs edge sharp and results in ribs with rounded edges. The one of the main objectives of the present study is to provide a fundamental understanding of the flow physics on the heat transfer and pressure drop behavior in 45(&)deg; ribbed channels both with sharp and rounded-edge ribs. It is found that the secondary flow has a significant effect on the heat transfer behavior for both types of ribs. There is a great need of high-fidelity PIV flow field data in the inter-rib space for an angled ribbed channel which can be used for CFD validation, especially for LES. The current study provides benchmarking flow field data in the inter-rib space in a square channel with 45(&)deg; ribs using stereoscopic PIV technique. Besides the experiments, numerical studies were also conducted by using LES and different RANS models. The LES results show an excellent prediction capability for aerothermal behavior in such channels. However, the prediction capability of RANS models is found to be inconsistent for different rib configurations and flow conditions.
Show less - Date Issued
- 2018
- Identifier
- CFE0007302, ucf:52171
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007302
- Title
- Analysis of Heat Transfer on Turbulence Generating Ribs using Dynamic Mode Decomposition.
- Creator
-
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
- Theoretical Paschen's Law Model for Aerospace Vehicles: Validation Experiment.
- Creator
-
Mulligan Aroche, Jaysen, Ahmed, Kareem, Kapat, Jayanta, Bhattacharya, Samik, University of Central Florida
- Abstract / Description
-
Aerospace vehicles often experience triboelectric charging while traversing the atmosphere. Triboelectric charging occurs when a material come into frictional contact with a different material. Aerospace vehicles triboelectrically charge due to frictional contact with dust and ice crystals suspended in the atmosphere. Launch vehicles traversing ice clouds in low-pressure atmosphere are especially prone to electrostatic discharge events (i.e. sparks). These conditions are hazardous and affect...
Show moreAerospace vehicles often experience triboelectric charging while traversing the atmosphere. Triboelectric charging occurs when a material come into frictional contact with a different material. Aerospace vehicles triboelectrically charge due to frictional contact with dust and ice crystals suspended in the atmosphere. Launch vehicles traversing ice clouds in low-pressure atmosphere are especially prone to electrostatic discharge events (i.e. sparks). These conditions are hazardous and affect the vehicle's launch commit criteria. In 2010, engineers from an ARES-I rocket launch reported concerns with triboelectric charging over their self-destruct system antenna. This concern was addressed by putting the antenna through harsh conditions in a laboratory environment. The need for laboratory testing could have been avoided if there was a mathematical model to predict these events. These discharge events can typically be predicted by the Classical Paschen's Law, which relates discharge voltage to pressure, material and distance between the charged and ground surfaces (i.e. electrodes). However, the Classical Paschen's Law does not capture any aerodynamic considerations such as large bulk flow and compressibility effects. It became apparent that a new model would be needed to predict a discharge voltage with aerodynamic considerations. This research focused on defining a theoretical model and providing experimental data to validate the model. The hypothesis of this work is that charged ions are removed too quickly for enough charge to build up and result in an electrostatic discharge at the voltage that is predicted by the Classical Paschen's Law. The wind tunnel testing for this experiment was conducted at the Center for Advanced Turbomachinery (&) Energy Research (CATER) facility. A charged electrode was exposed to flows at Mach numbers 1.5 to 3.5. It was found that the supersonic flow suppressed the electrostatic discharge events. The voltage required for an electrostatic discharge at supersonic conditions increased by a factor of three. The modified Paschen's Law can help in defining the launch commit criteria of aerospace vehicles.
Show less - Date Issued
- 2018
- Identifier
- CFE0007059, ucf:51994
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007059
- Title
- Ignition Studies of Oxy-Syngas/CO2 Mixtures Using Shock Tube for Cleaner Combustion Engines.
- Creator
-
Barak, Samuel, Vasu Sumathi, Subith, Kapat, Jayanta, Ahmed, Kareem, University of Central Florida
- Abstract / Description
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In this study, syngas combustion was investigated behind reflected shock waves in order to gain insight into the behavior of ignition delay times and effects of the CO2 dilution. Pressure and light emissions time-histories measurements were taken at a 2 cm axial location away from the end wall. High-speed visualization of the experiments from the end wall was also conducted. Oxy-syngas mixtures that were tested in the shock tube were diluted with CO2 fractions ranging from 60% - 85% by volume...
Show moreIn this study, syngas combustion was investigated behind reflected shock waves in order to gain insight into the behavior of ignition delay times and effects of the CO2 dilution. Pressure and light emissions time-histories measurements were taken at a 2 cm axial location away from the end wall. High-speed visualization of the experiments from the end wall was also conducted. Oxy-syngas mixtures that were tested in the shock tube were diluted with CO2 fractions ranging from 60% - 85% by volume. A 10% fuel concentration was consistently used throughout the experiments. This study looked at the effects of changing the equivalence ratios (?), between 0.33, 0.5, and 1.0 as well as changing the fuel ratio (?), hydrogen to carbon monoxide, from 0.25, 1.0 and 4.0. The study was performed at 1.61-1.77 atm and a temperature range of 1006-1162K. The high-speed imaging was performed through a quartz end wall with a Phantom V710 camera operated at 67,065 frames per second. From the experiments, when increasing the equivalence ratio, it resulted in a longer ignition delay time. In addition, when increasing the fuel ratio, a lower ignition delay time was observed. These trends are generally expected with this combustion reaction system. The high-speed imaging showed non-homogeneous combustion in the system, however, most of the light emissions were outside the visible light range where the camera is designed for. The results were compared to predictions of two combustion chemical kinetic mechanisms: GRI v3.0 and AramcoMech v2.0 mechanisms. In general, both mechanisms did not accurately predict the experimental data. The results showed that current models are inaccurate in predicting CO2 diluted environments for syngas combustion.
Show less - Date Issued
- 2018
- Identifier
- CFE0006974, ucf:52909
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006974
- Title
- Shock Tube Investigations of Novel Combustion Environments Towards a Carbon-Neutral Future.
- Creator
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Barak, Samuel, Vasu Sumathi, Subith, Kapat, Jayanta, Ahmed, Kareem, University of Central Florida
- Abstract / Description
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Supercritical carbon dioxide (sCO2) cycles are being investigated for the future of power generation. These cycles will contribute to a carbon-neutral future to combat the effects of climate change. These direct-fired closed cycles will produce power without adding significant pollutants to the atmosphere. For these cycles to be efficient, they will need to operate at significantly higher pressures (e.g., 300 atm for Allam Cycle) than existing systems (typically less than 40 atm). There is...
Show moreSupercritical carbon dioxide (sCO2) cycles are being investigated for the future of power generation. These cycles will contribute to a carbon-neutral future to combat the effects of climate change. These direct-fired closed cycles will produce power without adding significant pollutants to the atmosphere. For these cycles to be efficient, they will need to operate at significantly higher pressures (e.g., 300 atm for Allam Cycle) than existing systems (typically less than 40 atm). There is limited knowledge on combustion at these pressures or at the high dilution of carbon dioxide. Nominal fuel choices for gas turbines include natural gas and syngas (mixture of CO and H2). Shock tubes study these problems in order to understand the fundamentals and solve various challenges. Shock tube experiments have been studied by the author in the sCO2 regime for various fuels including natural gas, methane and syngas. Using the shock tube to take measurements, pressure and light emissions time-histories measurements were taken at a 2-cm axial location away from the end wall. Experiments for syngas at lower pressure utilized high-speed imaging through the end wall to investigate the effects of bifurcation. It was found that carbon dioxide created unique interactions with the shock tube compared to tradition bath gasses such as argon. The experimental results were compared to predictions from leading chemical kinetic mechanisms. In general, mechanisms can predict the experimental data for methane and other hydrocarbon fuels; however, the models overpredict for syngas mixtures. Reaction pathway analysis was evaluated to determine where the models need improvements. A new shock tube has been designed and built to operate up to 1000 atm pressures for future high-pressure experiments. Details of this new facility are included in this work. The experiments in this work are necessary for mechanism development to design an efficient combustor operate these cycles.
Show less - Date Issued
- 2019
- Identifier
- CFE0007781, ucf:52359
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007781
- Title
- Heat Transfer, Friction, and Turbulent Analysis on Single Ribbed-Wall Square Channel.
- Creator
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Vergos, Christopher, Kapat, Jayanta, Vasu Sumathi, Subith, Ahmed, Kareem, University of Central Florida
- Abstract / Description
-
An experimental investigation of heat transfer and friction behavior for a fully developed flow in a non-rotating square channel was conducted under a wide range of Reynolds numbers from 6,000 to 180,000. The rig used in this study was a single ribbed wall variant of Ahmed et al.'s [ 1 ] rig from which results of this rig were compared. Ahmed et al.'s rig was a replica of Han et al.'s square channel [ 2 ] used to validate their work, and expand the Reynolds number range for both heat transfer...
Show moreAn experimental investigation of heat transfer and friction behavior for a fully developed flow in a non-rotating square channel was conducted under a wide range of Reynolds numbers from 6,000 to 180,000. The rig used in this study was a single ribbed wall variant of Ahmed et al.'s [ 1 ] rig from which results of this rig were compared. Ahmed et al.'s rig was a replica of Han et al.'s square channel [ 2 ] used to validate their work, and expand the Reynolds number range for both heat transfer and friction data. The test section was 22 hydraulic diameters (Dh) long, and made of four aluminum plates. One rib roughened bottom wall, and three smooth walls bounded the flow. Glued brass ribs oriented at 45(&)deg; to the flow direction, with a ratio of rib height to channel hydraulic diameter (e/Dh) and a ratio of pitch to rib height (p/e) of 0.063 and 10, respectively, lined the bottom wall. A 20Dh long acrylic channel with a continuation of the test section's interior was attached at the inlet of the test section to confirm the fully developed flow. Heat transfer tests were conducted in a Reynolds number range of 20,000 to 150,000. During these tests, the four walls were held under isothermal conditions. Wall-averaged, and module-averaged Nusselt values were calculated from the log-mean temperature differences between the plate surface temperature and calculated, by energy balance, fluid bulk temperature. Streamwise Nusselt values become constant at an x/Dh of 8 within the tested Reynolds number range. Wall averaged Nusselt values were determined after x/Dh=8, and scaled by the Dittus-Boelter correlation, Nuo, for smooth ducts to yield a Nusselt augmentation value (Nu/Nuo). Non-heated friction tests were conducted from a Reynolds number range of 6,000 to 180,000. Pressure drop along the channel was recorded, and channel-averaged Darcy-Weisbach friction factor was calculated within the range of Reynolds number tested. Scaling the friction factor by the smooth-wall Blasius correlation, fo, gave the friction augmentation (f/fo). The thermal performance, a modified ratio of the Nusselt and friction augmentation used by Han et al. [ 2 ], was then calculated to evaluate the bottom-line performance of the rig. It was found that the Nusselt augmentation approached a constant value of 1.4 after a Reynolds number of 60,000 while friction augmentation continued to increase in a linear fashion past that point. This caused the overall thermal performance to decline as Reynolds number increased up to a certain point. Further studies were conducted in an all acrylic, non-heated variant of the rig to study the fluid flow in the streamwise direction on, and between two ribs in the fully developed region of the channel. Single-wire hot-wire anemometry characterized velocity magnitude profiles with great detail, as well as turbulence intensity for Reynolds numbers ranging from 5,000 to 50,000. As the Reynolds number increased the reattachment point between two ribs remained about stationary while the turbulence intensity receded to the trailing surface of the upstream rib, and dissipated as it traveled. At low Reynolds numbers, between 5,000 and 10,000, the velocity and turbulence intensity streamwise profiles seemed to form two distinct flow regions, indicating that the flow over the upstream rib never completely attached between the two ribs. Integral length-scales were also derived from the autocorrelation function using the most turbulent signal acquired at each Reynolds number. It was found that there is a linear trend between Reynolds number and the integral length-scale at the most turbulent points in the flow. For example, at Re=50,000 the most the length scale found just past the first rib was on the order of two times the height of the rib. Rivir et al. [ 30 ] found in a similar case that at Re = 45,000, it was 1.5 times the rib height. Several factors could influence the value of this integral length-scale, but the fact that their scale is on the order of what was obtained in this case gives some level of confidence in the value.
Show less - Date Issued
- 2017
- Identifier
- CFE0007138, ucf:52318
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007138
- Title
- Ellipsometric Measurements of Alternative Fuels.
- Creator
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Nash, Leigh, Vasu Sumathi, Subith, Kapat, Jayanta, Ahmed, Kareem, University of Central Florida
- Abstract / Description
-
Alternative jet fuels will be important in the future to ensure cleaner burning, reliable, and reasonably priced air transportation. One important property that must meet certification standards is the fuel's thermal stability, or its ability to withstand heating before breaking down. Jet fuels are used as engine coolants, and thermally unstable fuels can form deposits in the fuel delivery systems, leading to a loss of fuel flow. In the past, the thermal stability of a fuel was rated using a...
Show moreAlternative jet fuels will be important in the future to ensure cleaner burning, reliable, and reasonably priced air transportation. One important property that must meet certification standards is the fuel's thermal stability, or its ability to withstand heating before breaking down. Jet fuels are used as engine coolants, and thermally unstable fuels can form deposits in the fuel delivery systems, leading to a loss of fuel flow. In the past, the thermal stability of a fuel was rated using a color standard method. The color of the deposit left on a metal tube that had been heated and exposed to a test fuel were matched with a color standard to rate the level of deposition, and thus the fuel's thermal stability. Ellipsometry, which is an optical technique that uses changes in a beam of light's polarization after it reflects off a sample to determine the thickness of any film on that sample, has recently been implemented to improve the thermal stability characterization standard.Various aspects of the ellipsometric method have been investigated in this work. In addition, several thermal stability studies were carried out. The effect of increasing temperature on the thermal stability of Sasol Iso-Paraffinic Kerosene, Jet A, JP-8, and Gevo jet fuel have been analyzed, and the effect of varying levels of the additive naphthalene in Sasol IPK has also been investigated. Various theoretical optical models have been evaluated for their ability to predict deposit thickness. Finally, attempts to validate these measurements were made using scanning electron microscopy, ellipsometric tube rating, interferometric tube rating, and reference tubes. The analysis carried out in this work was used to make recommendations for improving the thermal stability test standard.
Show less - Date Issued
- 2017
- Identifier
- CFE0007130, ucf:52323
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007130
- Title
- Investigation into the Feasibility of Adding Turbulators to Rocket Combustion Chamber Cooling Channels Using a Conjugate Heat Transfer Analysis.
- Creator
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Buchanan, Tyler, Kapat, Jayanta, Raghavan, Seetha, Ghosh, Ranajay, University of Central Florida
- Abstract / Description
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A conjugate heat transfer analysis will be carried out to simulate an 89 kN thrust chamber hydrogen cooling channel, to determine the feasibility of adding turbulators to the combustion chamber cooling channels at various parameters such as angle, pitch, and height of the turbulator. An existing regeneratively cooled chamber environment is simulated and used as a baseline case to be compared against. The new design includes using ribbed turbulators or delta wedges in the cooling channels to...
Show moreA conjugate heat transfer analysis will be carried out to simulate an 89 kN thrust chamber hydrogen cooling channel, to determine the feasibility of adding turbulators to the combustion chamber cooling channels at various parameters such as angle, pitch, and height of the turbulator. An existing regeneratively cooled chamber environment is simulated and used as a baseline case to be compared against. The new design includes using ribbed turbulators or delta wedges in the cooling channels to increase the heat transfer on the channel hot wall (wall adjacent to the hot gas wall) and on the two channel sidewalls. With a higher heat transfer coefficient, the sidewalls behave like fins for heat transfer and participate more in the overall heat transfer process in the channel. Efficient rib and wedge geometries are chosen based on previous investigations. A conjugate heat transfer analysis is performed using a straight duct with the rib and wedge geometries included, with boundary conditions similar to those found in the combustion chamber, to provide thermal hydraulic performance data at numerous turbulator configurations. The baseline channel's maximum hot wall temperature is the target maximum hot wall temperature that is desired to be reduced. The goal is to reduce the hot gas side wall temperature at a minimal cost in pressure drop.
Show less - Date Issued
- 2018
- Identifier
- CFE0007160, ucf:52320
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007160
- 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
- Development of a Single Sensor Approach for Capturing Three-Dimensional, Time Resolved Flame and Velocity Information.
- Creator
-
Reyes, Jonathan, Ahmed, Kareem, Kassab, Alain, Kapat, Jayanta, University of Central Florida
- Abstract / Description
-
Performing non-intrusive measurements is the key to acquiring accurate information representative of what is being observed. The act of measuring often changes the environment being observed altering the information that is being obtained. Due to this, the community of fluid scientists have gravitated towards using laser-based measurements to observe the phenomena occurring in their experiments. The study of fluids has advanced since this point, utilizing techniques such as planar laser...
Show morePerforming non-intrusive measurements is the key to acquiring accurate information representative of what is being observed. The act of measuring often changes the environment being observed altering the information that is being obtained. Due to this, the community of fluid scientists have gravitated towards using laser-based measurements to observe the phenomena occurring in their experiments. The study of fluids has advanced since this point, utilizing techniques such as planar laser induced florescence (PLIF), particle image velocimetry (PIV), laser doppler velocimetry (LDV), particle doppler anemometry (PDA), etc. to acquire chemical species information and velocity information. These techniques, though, are inherently two-dimensional and cannot fully describe a flow field. In the area of reacting flow fields (combustion) acquiring the local fuel to air ratio information is increasingly important. Without it, scientist must rely on global one-dimensional metering techniques to correlate the fuel to air ratio of their flow field of interest. By knowing the fuel to air ratio locally and spatially across a flame, the location of products and reactants can be deduced, giving insight into any inefficiencies associated with a burner. Knowing the spatial fuel air field also gives insights into the density gradient associated with the flow field. Discussed in this work will be the development of a non-intrusive local fuel-air measurement technique and an expansion of the PIV technique into the third dimension, tomographic PIV, utilizing only one camera to do so for each measurement. The local fuel-air measurement is performed by recording two species (C2* and CH*) simultaneously and calibrating their ratio to the known fuel-air field. Tomographic PIV is performed by utilizing fiber coupling to acquire multiple viewpoints utilizing a single camera.
Show less - Date Issued
- 2019
- Identifier
- CFE0007523, ucf:52602
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007523
- Title
- Investigation of Flow Field Structures in a Rectangular Channel with a Pin Fin Array.
- Creator
-
Tran, Patrick, Kapat, Jayanta, Bhattacharya, Samik, Huang, Helen, University of Central Florida
- Abstract / Description
-
Pin fin arrays are commonly found in heat exchangers, turbine blades, and electronic heat sinks. Fin arrays are extended surfaces that are used as turbulence promoters by inducing horseshoe vortex (HSV) and von Karman vortex (KV) structures. The horseshoe vortex are primarily studied in the leading edge of the blunt body, whereas the KV are formed in the trailing side. This study presents an experimental investigation of flow field structures and pressure loss on staggered pin fin array in...
Show morePin fin arrays are commonly found in heat exchangers, turbine blades, and electronic heat sinks. Fin arrays are extended surfaces that are used as turbulence promoters by inducing horseshoe vortex (HSV) and von Karman vortex (KV) structures. The horseshoe vortex are primarily studied in the leading edge of the blunt body, whereas the KV are formed in the trailing side. This study presents an experimental investigation of flow field structures and pressure loss on staggered pin fin array in the wake region, where KV are dominate. These flow structures increase the local levels turbulence and generate eddies that promote flow mixing, which in turn allows for higher levels of heat transfer. Improvement in heat transfer can increase the efficiency of the heat exchanger by reducing the thermal load and stress on the components which can extended product life. A study of the vortex shedding using a Particle Image Velocimetry (PIV) technique is used to measure flow field using a closed loop vertical water tunnel. A Time Resolved Particle Image Velocimetry (TR-PIV) study for both steady and unsteady flow structures in the fully developed region of a pin fin array at multiple wall normal cross sections are performed. The pin fin array consists of circular pin fins with 8 rows of 7.5 pins in rectangular channel with Reynolds number varying from 10,000 to 20,000. The Pin array is in a staggered configuration with stream wise (Y/D) spacing of 2.5 and span wise (X/D) spacing of 2.5, and height to pin diameter (H/D) of 2. A supplemental computation fluid dynamic (CFD) study is also for comparison with the PIV flow field. The goal of the present study is to determine the major vortex structures that found the flow at different Z/D, quantify parameters that numerical methods are unable to solve, and provide a base line for other parameters that can be used to improve the accuracy of numerical models. The novelty of this work is to provide data and characterize the near the viscous sub layer of Z/D =0.
Show less - Date Issued
- 2019
- Identifier
- CFE0007736, ucf:52446
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007736