VTechWorks Repository :: Browsing by Author "Thole, Karen A."

Browsing by Author "Thole, Karen A."

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Adiabatic Effectiveness Measurements of Leakage Flows along the Hub Region of Gas Turbine Engines
Ranson, William Wayne (Virginia Tech, 2004-05-11)
To prevent melting of turbine blades, numerous cooling schemes have been developed to cool the blades using cooler air from the compressor. Unfortunately, the clearance gap between adjacent hub sections allows coolant to leak into the hub region. Coolant flow also leaks into the hub region through gaps between individual stages. The results of a combined experimental and computational study of cooling along the hub of a first stage turbine blade caused by leakage flows are discussed in detail. Additionally, this study examines a novel cooling feature, called a microcircuit, which combines internal convective cooling with external film cooling. For the experimental investigation, scaled up blades were tested in a low speed wind tunnel. Adiabatic effectiveness measurements were made with infrared thermography of the entire hub region for a range of leakage flow conditions. For the computations, a commercially available computational fluid dynamics (CFD) code, FLUENT 6.0, was used to simulate the various flows. Results show that featherseal leakage flows provide small cooling benefits to the hub. Increases in featherseal flow provide no additional cooling to the hub region. Unlike the featherseal, leakage flows from the front rim provide ample cooling to the hub region, especially the leading edge of the blade passage. None of the leakage flows provide significant cooling to the pressure side region of the hub or trailing edge suction side. With the addition of the hub microcircuits, there is improved hub cooling of the suction side of the blades. Though the coolant exit uniformity was low and affected by the featherseal flow, the microcircuits were shown to provide more cooling along the hub region. Good agreements were observed between the computational and experimental results, though computations over-predicted front rim cooling and microcircuit uniformity.
ADVANCE Institutional Transformation Grant Proposal: Virginia Tech
Hyer, Patricia B.; Thole, Karen A.; Love, Nancy G. (2002)
Virginia Tech proposes a comprehensive program to promote and enhance the careers of women in science and engineering. The project has four major program elements that address institutional barriers that have constrained the advancement of women faculty members in the sciences and engineering (S&E) and target institutional culture, practices, and leadership development needs specific to Virginia Tech. The four program elements are listed here, with outcome measures and process activities that support each element.

Institutionalizing change
Measurable Outcome: A change in the awareness, attitudes, and behaviors of key administrators and faculty members in S&E regarding gender equity issues.

Project Activities: retreats and workgroups for faculty and academic leaders, site visits to or interaction with other ADVANCE projects, qualitative assessment of the experience of women faculty in S&E, and review of policies and programs.

Empowering women as leaders and scholars
Measurable Outcome: A significant increase in the percentage of women in visible positions as academic and technical leaders and as senior scholars in S&E.

Project Activities: half-time placements in leadership roles, research grants, faculty development, a named lecture series, and a flexible work/life fund.

Increasing the representation of women
Measurable Outcome: A significant increase in the percentage of women faculty in S&E.

Project Activities: intensive work with search committees, visits to other campuses and conferences, and incentives for faculty involvement in recruitment activities.

Advancing women into faculty careers

Measurable Outcome: A significant increase in the percentage of women in S&E who choose faculty careers.

Project Activities: program to prepare the future professoriate and expanded dissertation year/postdoctoral fellowship program.
Aerodynamic Force and Pressure Loss Measurements on Low Aspect Ratio Pin Fin Arrays
Thrift, Alan Albright (Virginia Tech, 2007-02-09)
The desire to achieve higher heat transfer augmentation for turbine blades is fueled by the increased power output and efficiency that is achievable with high turbine inlet temperatures. The use of internal cooling channels fitted with pin fin arrays serves as one method of accomplishing this goal. Consequently, the addition of pin fin arrays comes at the expense of increased pressure drop. Therefore the pin fin geometry must be judiciously chosen to achieve the required heat transfer rate while minimizing the associated pressure drop. This project culminates in the measurement of both pin fin force and array pressure drop as they related to changes in the array geometry. Specifically, the effects of Reynolds number, spanwise pin spacing, streamwise pin spacing, pin aspect ratio, and flow incidence angle. Direct two-component force measurement is achieved with a cantilever beam force sensor that uses highly sensitive piezoresistive strain gauges, relating the strain at the base of the beam to the applied force. With proper characterization, forces as small as one-tenth the weight of a paper clip are successfully measured. Additionally, array pressure drop measurements are achieved using static pressure taps. Experiments were conducted over a range of Reynolds numbers between 7,500 and 35,000. Changes in the spanwise pin spacing were shown to substantially alter the pin fin drag and array pressure drop, while changes in the streamwise pin spacing were less influential. The experimental results also showed a dramatic reduction in the pin fin drag and array pressure drop for an inline flow incidence angle. Finally, changes in the pin aspect ratio were shown to have little effect on the array pressure drop.
An Application of Wavelet Techniques to Bi-directionality in the Monte Carlo Ray Trace Environment
Smith, Dwight Eldridge (Virginia Tech, 2002-12-16)
This dissertation presents three different aspects of the incorporation of directionality into the Monte Carlo ray-trace (MCRT) environment: (1) the development of a methodology for using directional surface optical data, (2) the measurement of the bi-directional reflectivity functions for two different surfaces, and (3) MCRT simulations performed using these directional data sets. The methodology presented is based upon a rigorous analytical formulation and is capable of performing simulations of radiation exchange involving directional emission, absorption and reflection given the bi-directional reflectivity functions (BDRF) of the participating surfaces. A wavelet compression technique is presented for the management of extremely large directional data sets. The BDRFs of two different surfaces were acquired using a Surface Optics Corporation model SOC-250 bi-directional reflectometer. These data were processed according to the methodology presented and an MCRT code was used to simulate the action of the SOC-250 in measuring radiant energy reflected from the surfaces of the two samples when illuminated by the source of the SOC-250. Another MCRT code was used to simulate the radiant energy reflected into a plane at the exit of an open-ended rectangular box when the entrance to the box is illuminated by source of the SOC-250. The RMS error between the MCRT simulations of sampling using the SOC-250 and the measured data were determined and then divided by the mean BDRF level of the measured data (RMS/mean[rho]) to provide an estimate of convergence. The RMS/mean[rho] was observed to fall from as much as 138 to 0.84 for the aluminum substrate coated with Krylon Shortcuts Hunter Green Satin aerosol paint as the number of energy bundles emitted in the MCRT simulation went from 103 to 106 at an incident zenith angle of 40 deg. The RMS/mean[rho] was observed to fall from as much as 2.2 to 0.2 for the Norton (150 Fine grit) all-purpose sandpaper coated with Krylon Shortcuts Hunter Green Satin aerosol paint as the number of energy bundles emitted in the MCRT simulation went from 103 to 106 at an incident zenith angle of 40 deg.
Assessment of a Leading Edge Fillet for Decreasing Vane Endwall Temperatures in a Gas Turbine Engine
Lethander, Andrew Tait (Virginia Tech, 2003-12-01)
The objective of this investigation was to improve the thermal environment for a turbine vane through reduction of passage secondary flows. This was accomplished by modifying the vane/endwall junction to include a leading edge fillet. The problem approach was to integrate optimization methods with computational fluid dynamics to optimize the fillet design. The resulting leading edge fillet was then tested in a large-scale, low speed cascade to verify thermal performance. A combustor simulator located upstream of the cascade was used to generate realistic inlet conditions for the turbine vane. Both computational and experimental results underscore the importance of properly modeling the inlet conditions to the turbine. Results of the computational optimization process indicate that significant reductions in adiabatic wall temperature can be achieved with a leading edge fillet. While the intent of the initial fillet design was to improve the thermal environment for the vane endwall, computational results also indicate thermal benefit to the vane surfaces. Flow and thermal field results show that a fillet can enhance coolant effectiveness, prevent formation of the leading edge horseshoe vortex, and preclude full development of a passage vortex. In experimental testing, four cascade inlet conditions were investigated to evaluate the effectiveness of the fillet in reducing endwall temperature levels. Two tested conditions featured a flush combustor/cascade interface, while the remaining two included coolant injection through a backward-facing slot. With the flush interface, fillet thermal performance was evaluated for two inlet total pressure profiles. For the design profile, the fillet had a positive impact on the endwall temperature distribution as well as on the passage thermal field. For the off-design profile, the fillet was observed to have a slightly detrimental impact on the endwall adiabatic temperature distribution; however, passage thermal field results indicate a thermal benefit for the vane suction surface. With the backward-facing slot, thermal tests were conducted for two slot coolant flow rates. For both slot flow rates, the fillet improved endwall thermal protection and prevented coolant lift-off. While increasing the flow rate of slot coolant enhanced endwall effectiveness, fillet thermal performance was similar for the two slot flow rates.
Comparison of the Thermal Performance of Several Tip Cooling Designs for a Turbine Blade
Christophel, Jesse Reuben (Virginia Tech, 2003-09-19)
Gas turbine blades are subject to harsh operating conditions that require innovative cooling techniques to insure reliable operation of parts. Film-cooling and internal cooling techniques can prolong blade life and allow for higher engine temperatures. This study examines several unique methods of cooling the turbine blade tip. The first method employs holes placed directly in the tip which inject coolant onto the blade tip. The second and third methods used holes placed on the pressure side of a blade near the tip representative of two different manufacturing techniques. The fourth method is a novel cooling technique called a microcircuit, which combines internal convection and injection from the pressure side near a turbine blade tip. Wind tunnel tests are used to observe how effectively these designs cool the tip through adiabatic effectiveness measurements and convective heat transfer measurements. Tip gap size and blowing ratio are varied for the different tip cooling configurations. Results from these studies show that coolant injection from either the tip surface or from the pressure side near the tip are viable cooling methods. All of these studies showed better cooling could be achieved at small tip gaps than large tip gaps. The results in which the two different manufacturing techniques were compared indicated that the technique producing more of a diffused hole provided better cooling on the tip. When comparing the thermal performance of all the cooling schemes investigated, the added benefit of the internal convective cooling shows that the microcircuit outperforms the other designs.
Design and Benchmarking of a Combustor Simulator Relevant to Gas Turbine Engines
Barringer, Michael David (Virginia Tech, 2001-09-20)
An experimental facility was designed and benchmarked that could simulate the non-uniformities in the flow and thermal fields exiting real gas-turbine combustors. The design of the combustor simulator required analyses of the flow paths within a real combustor in a gas turbine engine. Modifications were made to an existing wind tunnel facility to allow for the installation of the combustor simulator. The overall performance of the simulator was then benchmarked through measurements of velocity, pressure, temperature, and turbulence using a straight exit test section to provide a baseline set of data. Comparisons of the measured quantities were made between two test cases that included a flow field with and without dilution flow.One of the major findings from this study was that the total pressure profiles exiting the combustor simulator in the near-wall region were different from a turbulent boundary layer. This is significant since many studies consider a turbulent boundary layer as the inlet condition to the turbine. Turbulent integral length scales were found to scale well with the dilution hole diameters and no dominant frequencies were observed in the streamwise velocity energy spectra. Dilution flow resulted in an increase in turbulence levels and mixing causing a reduction in the variation of total pressure and velocity. Adiabatic effectiveness levels were significantly reduced for the case with dilution flow in both the near combustor exit region and along the axial length of the straight exit test section.
A Detailed Study of Fan-Shaped Film-Cooling for a Nozzle Guide Vane for an Industrial Gas Turbine
Colban, William F. IV (Virginia Tech, 2005-11-28)
The goal of a gas turbine engine designer is to reduce the amount of coolant used to cool the critical turbine surfaces, while at the same time extracting more benefit from the coolant flow that is used. Fan-shaped holes offer this opportunity, reducing the normal jet momentum and spreading the coolant in the lateral direction providing better surface coverage. The main drawback of fan-shaped cooling holes is the added manufacturing cost from the need for electrical discharge machining instead of the laser drilling used for cylindrical holes. This research focused on examining the performance of fan-shaped holes on two critical turbine surfaces; the vane and endwall. This research was the first to offer a complete characterization of film-cooling on a turbine vane surface, both in single and multiple row configurations. Infrared thermography was used to measure adiabatic wall temperatures, and a unique rigorous image transformation routine was developed to unwrap the surface images. Film-cooling computations were also done comparing the performance of two popular turbulence models, the RNG-kε and the v2-f model, in predicting film-cooling effectiveness. Results showed that the RNG-kε offered the closest prediction in terms of averaged effectiveness along the vane surface. The v2-f model more accurately predicted the separated flow at the leading edge and on the suction side, but did not predict the lateral jet spreading well, which led to an over-prediction in film-cooling effectiveness. The intent for the endwall surface was to directly compare the cooling and aerodynamic performance of cylindrical holes to fan-shaped holes. This was the first direct comparison of the two geometries on the endwall. The effect of upstream injection and elevated inlet freestream turbulence was also investigated for both hole geometries. Results indicated that fan-shaped film-cooling holes provided an increase in film-cooling effectiveness of 75% on average above cylindrical film-cooling holes, while at the same time producing less total pressure losses through the passage. The effect of upstream injection was to saturate the near wall flow with coolant, increasing effectiveness levels in the downstream passage, while high freestream turbulence generally lowered effectiveness levels on the endwall.
Developing and Testing a Combustor Simulator For Investigating High Pressure Turbine Aerodynamics and Heat Transfer
Barringer, Michael David (Virginia Tech, 2006-07-20)
Within a gas turbine engine, the turbine nozzle guide vanes are subjected to very harsh conditions from the highly turbulent and hot gases exiting the combustor. The temperature and pressure fields exiting combustors are highly nonuniform and dictate the heat transfer and aero losses that occur in the turbine passages. To better understand these effects, the goal of this work was to develop an adjustable combustor exit profile simulator for the Turbine Research Facility (TRF) at the Air Force Research Laboratory. The TRF is a high temperature, high pressure, short duration blow-down test facility that is capable of matching several aerodynamic and thermal nondimensional engine parameters including Reynolds number, Mach number, pressure ratio, corrected mass flow, gas to metal temperature ratio, and corrected speed. The primary research objective was to design, install, and verify a non-reacting simulator device that can provide representative combustor exit total pressure and temperature profiles to the inlet of the TRF turbine test section. This required the upstream section of the facility to be redesigned into multiple concentric annuli that serve the purpose of injecting high momentum dilution jets and low momentum film cooling jets into a central annular chamber, similar to a turbine engine combustor. The design of the section allows for variations in injection levels to generate different pressure profiles with elevated turbulence. The dilution and film cooling temperatures can also be varied to create a variety of exit temperature profiles similar to real combustors. The impact of the generated temperature and pressure profiles on turbine heat transfer and secondary flow development was ultimately investigated. Proposed optimal inlet conditions for the turbine tested in this research effort were determined based on the measured data corresponding to the combustor simulator exit profiles that minimized vane heat transfer and total pressure loss.
Development of a Methodology to Measure Aerodynamic Forces on Pin Fins in Channel Flow
Brumbaugh, Scott J. (Virginia Tech, 2006-01-05)
The desire for smaller, faster, and more efficient products places a strain on thermal management in components ranging from gas turbine blades to computers. Heat exchangers that utilize internal cooling flows have shown promise in both of these industries. Although pin fins are often placed in the cooling channels to augment heat transfer, their addition comes at the expense of increased pressure drop. Consequently, the pin fin geometry must be judiciously chosen to achieve the desired heat transfer rate while minimizing the pressure drop and accompanying pumping requirements. This project culminates in the construction of a new test facility and the development of a unique force measurement methodology. Direct force measurement is achieved with a cantilever beam force sensor that uses sensitive piezoresistive strain gauges to simultaneously measure aerodynamic lift and drag forces on a pin fin. After eliminating the detrimental environmental influences, forces as small as one-tenth the weight of a paper clip are successfully measured. Although the drag of an infinitely long cylinder in uniform cross flow is well documented, the literature does not discuss the aerodynamic forces on a cylinder with an aspect ratio of unity in channel flow. Measured results indicate that the drag coefficient of a cylindrical pin in a single row array is greater than the drag coefficient of an infinite cylinder in cross flow. This phenomenon is believed to be caused by an augmentation of viscous drag on the pin fin induced by the increased viscous effects inherent in channel flow.
Development of a Thermal Management Methodology for a Front-End DPS Power Supply
Sewall, Evan Andrew (Virginia Tech, 2002-10-11)
Thermal management is a rapidly growing field in power electronics today. As power supply systems are designed with higher power density levels, keeping component temperatures within suitable ranges of their maximum operating limits becomes an increasingly challenging task. This project focuses on thermal management at the system level, using a 1.2 kW front-end power converter as a subject for case study. The establishment of a methodology for using the computer code I-deas to computationally simulate the thermal performance of component temperatures within the system was the primary goal. A series of four benchmarking studies was used to verify the computational predictions. The first test compares predictions of a real system with thermocouple measurements, and the second compares computational predictions with infrared camera and thermocouple measurements on a component mounted to a heat sink. The third experiment involves using flow visualization to verify the presence of vortices in the flow field, and the fourth is a comparison of computational temperature predictions of a DC heater in a controlled flow environment. A radiation study using the Monte Carlo ray-trace method for radiation heat transfer resulted in the reduction of some component temperature predictions of significant components. This radiation study focused on an aspect of heat transfer that is often ignored in power electronics. A component rearrangement study was performed to establish a set of guidelines for component placement in future electronic systems. This was done through the use of a test matrix in which the converter layout was varied a number of different ways in order to help determine thermal effects. Based on the options explored and the electrical constraints on the circuit, an optimum circuit layout was suggested for maximum thermal performance. This project provides a foundation for the thermal management of power electronics at the system level. The use of I-deas as a computational modeling tool was explored, and comparison of the code with experimental measurements helped to explore the accuracy of I-deas as a system level thermal modeling tool.
The Effect of Endwall Contouring On Boundary Layer Development in a Turbine Blade Passage
Lynch, Stephen P. (Virginia Tech, 2011-08-31)
Increased efficiency and durability of gas turbine components is driven by demands for reduced fuel consumption and increased reliability in aircraft and power generation applications. The complex flow near the endwall of an axial gas turbine has been identified as a significant contributing factor to aerodynamic loss and increased part temperatures. Three-dimensional (non-axisymmetric) contouring of the endwall surface has been shown to reduce aerodynamic losses, but the effect of the contouring on endwall heat transfer is not well understood. This research focused on understanding the general flow physics of contouring and the sensitivity of the contouring to perturbations arising from leakage features present in an engine. Two scaled low-speed cascades were designed for spatially-resolved measurements of endwall heat transfer and film cooling. One cascade was intended for flat and contoured endwall studies without considering typical engine leakage features. The other cascade modeled the gaps present between a stator and rotor and between adjacent blades on a wheel, in addition to the non-axisymmetric endwall contouring. Comparisons between a flat and contoured endwall showed that the contour increased endwall heat transfer and increased turbulence in the forward portion of the passage due to displacement of the horseshoe vortex. However, the contour decreased heat transfer further into the passage, particularly in regions of high heat transfer, due to delayed development of the passage vortex and reduced boundary layer skew. Realistic leakage features such as the stator-rotor rim seal had a significant effect on the endwall heat transfer, although leakage flow from the rim seal only affected the horseshoe vortex. The contours studied were not effective at reducing the impact of secondary flows on endwall heat transfer and loss when realistic leakage features were also considered. The most significant factor in loss generation and high levels of endwall heat transfer was the presence of a platform gap between adjacent airfoils.
The Effects of Free Stream Turbulence on the Flow Field through a Compressor Cascade
Muthanna, Chittiappa (Virginia Tech, 2002-05-24)
The flow through a compressor cascade with tip leakage has been studied experimentally. The cascade of GE rotor B section blades had an inlet angle of 65.1Âº, a stagger angle of 56.9Âº, and a solidity of 1.08. The final turning angle of the cascade was 11.8Âº. This compressor configuration was representative of the core compressor of an aircraft engine. The cascade was operated with a tip gap of 1.65%, and operated at a Reynolds number based on the chord length (0.254 m) of 388,000. Measurements were made at 8 axial locations to reveal the structure of the flow as it evolved through the cascade. Measurements were also made to reveal the effects of grid generated turbulence on this flow. The data set is unique in that not only does it give a comparison of elevated free stream turbulence effects, but also documents the developing flow through the blade row of a compressor cascade with tip leakage. Measurements were made at a total of 8 locations 0.8, 0.23 axial chords upstream and 0, 0.27, 0.48, 0.77, 0.98, and 1.26 axial chords downstream of the leading edge of the blade row for both inflow turbulence cases. The measurements revealed the formation and development of the tip leakage vortex within the passage. The tip leakage vortex becomes apparent at approximately X/ca= 0.27 and dominated much of the endwall flow. The tip leakage vortex is characterized by high streamwise velocity deficits, high vorticity and high turbulence kinetic energy levels. The result showed that between 0.77 and 0.98 axial chords downstream of the leading edge, the vortex structure and behavior changes. The effects of grid generated turbulence were also documented. The results revealed significant effects on the flow field. The results showed a 4% decrease in the blade loading and a 20% reduction in the vorticity levels within tip leakage vortex. There was also a shift in the vortex path, showing a shift close to the suction side with grid generated turbulence, indicating the strength of the vortex was decreased. Circulation calculations showed this reduction, and also indicated that the tip leakage vortex increased in size by about 30%. The results revealed that overall, the turbulence kinetic energy levels in the tip leakage vortex were increased, with the most drastic change occurring at X/ca= 0.77.
Effects of Freestream Turbulence, Turbulence Length Scale, and Reynolds Number on Turbine Blade Heat Transfer in a Transonic Cascade
Carullo, Jeffrey Stephen (Virginia Tech, 2006-12-11)
This paper experimentally investigates the effect of high freestream turbulence intensity, turbulence length scale, and exit Reynolds number on the surface heat transfer distribution of a turbine blade at realistic engine Mach numbers. Passive turbulence grids were used to generate freestream turbulence levels of 2%, 12%, and 14% at the cascade inlet. The turbulence grids produced length scales normalized by the blade pitch of 0.02, 0.26, and 0.41, respectively. Surface heat transfer measurements were made at the midspan of the blade using thin film gauges. Experiments were performed at exit Mach numbers of 0.55, 0.78 and 1.03 which represent flow conditions below, near, and above nominal conditions. The exit Mach numbers tested correspond to exit Reynolds numbers of 6 x 105, 8 x 105, and 11 x 105, based upon true chord. The experimental results showed that the high freestream turbulence augmented the heat transfer on both the pressure and suction sides of the blade as compared to the low freestream turbulence case. At nominal conditions, exit Mach 0.78, average heat transfer augmentations of 23% and 35% were observed on the pressure side and suction side of the blade, respectively.
Effects of High Intensity, Large-Scale Freestream Combustor Turbulence On Heat Transfer in Transonic Turbine Blades
Nix, Andrew Carl (Virginia Tech, 2003-04-04)
The influence of freestream turbulence representative of the flow downstream of a modern gas turbine combustor and first stage vane on turbine blade heat transfer has been measured and analytically modeled in a linear, transonic turbine cascade. Measurements were performed on a high turning, transonic turbine blade. The facility is capable of heated flow with inlet total temperature of 120C and inlet total pressure of 10 psig. The Reynolds number based on blade chord and exit conditions (5x106) and the inlet and exit Mach numbers (0.4 and 1.2, respectively) are representative of conditions in a modern gas turbine engine. High intensity, large length-scale freestream turbulence was generated using a passive turbulence-generating grid to simulate the turbulence generated in modern combustors after it has passed through the first stage vane row. The grid produced freestream turbulence with intensity of approximately 10-12% and an integral length scale of 2 cm near the entrance of the cascade passages, which is believed to be representative of the core flow entering a first stage gas turbine rotor blade row. Mean heat transfer results showed an increase in heat transfer coefficient of approximately 8% on the suction surface of the blade, with increases on the pressure surface on the order of two times higher than on the suction surface (approximately 17%). This corresponds to increases in blade surface temperature of 5-10%, which can significantly reduce the life of a turbine blade. The heat transfer data were compared with correlations from published literature with good agreement. Time-resolved surface heat transfer and passage velocity measurements were performed to investigate and quantify the effects of the turbulence on heat transfer and to correlate velocity fluctuations with heat transfer fluctuations. The data demonstrates strong coherence in velocity and heat flux at a frequency correlating with the most energetic eddies in the turbulence flow field (the integral length-scale). An analytical model was developed to predict increases in surface heat transfer due to freestream turbulence based on local measurements of turbulent velocity fluctuations (u'RMS) and length-scale (Lx). The model was shown to predict measured increases in heat flux on both blade surfaces in the current data. The model also successfully predicted the increases in heat transfer measured in other work in the literature, encompassing different geometries (flat plate, cylinder, turbine vane and turbine blade) as well as both laminar and turbulent boundary layers, but demonstrated limitations in predicting early transition and heat transfer in turbulent boundary layers. Model analyses in the frequency domain provided valuable insight into the scales of turbulence that are most effective at increasing surface heat transfer.
Effects of Louver Length and Vortex Generators to Augment Tube Wall Heat Transfer in Louvered Fin Heat Exchangers
Sanders, Paul Alan (Virginia Tech, 2005-09-14)
There are several different types of compact heat exchangers used in applications where small size and weight are required. One particular type of compact heat exchanger, the louvered fin heat exchanger, has been used heavily in the automotive and air conditioning industries. Over the last several decades, the majority of the work towards improving louvered fin exchanger efficiency has focused on designing more efficient fins by optimizing fin parameters like louver angle, fin pitch, louver pitch, and louver length. At this point in time, many improvements to standard louver geometry have been made, so other surfaces and methods of enhancing exchanger performance need to be studied if any significant future efficiency gains are to be expected. This thesis presents a detailed experimental study that has two major foci relative to the performance of the louvered fin compact heat exchanger. The first is to determine the effect of louver length on pressure drop and tube wall heat transfer, which is the primary heat transfer surface in the heat exchanger. The second is to augment tube wall heat transfer with the use of delta winglets placed on the fins near the tube wall. These studies were completed on a 20X scale model of a louvered fin exchanger with a fin pitch to louver pitch ratio of 0.76 and a louver angle of 27°, over a Reynolds number range based on louver pitch of 230 < ReLp < 1016. The three louver lengths evaluated were 100%, 82%, and 70% of the fin height and delta winglet experiments were performed for louver length to fin pitch ratios of 100% and 70%. Heat transfer results for the louver length tests show that decreasing louver length leads to increases in tube wall heat transfer of 0% to 50% depending on Reynolds number. Also, delta winglets placed on the fins near the tube wall have been shown to produce average tube wall heat transfer augmentations of up to 52%.
Effects of Realistic Combustor Exit Profiles on a Turbine Vane Endwall
Colban, William Frederick IV (Virginia Tech, 2002-01-04)
Engine designers continually push the combustor exit temperature higher to produce more power from gas turbine engines. These high turbine inlet temperatures, coupled with high turbulence levels and flow field non-uniformities, make turbine vane and endwall cooling a very critical issue in engine design. To appropriately cool these surfaces, knowledge of the passage flow field and endwall temperature distribution at representative engine conditions is necessary. A combustor test section was used to simulate realistic turbine inlet profiles of turbulence, normalized temperature, normalized total pressure, and normalized streamwise velocity to study the flow field in a turbine vane passage and the adiabatic temperature distribution on the endwall. The combustor liner film-cooling and exit slot flows were varied independently to determine their relative effect on endwall cooling in the downstream turbine vane. Flow field measurements revealed the presence of a previously unmeasured third vortex in the vane passage. The tertiary vortex was located above the passage vortex and had rotation opposite to the passage vortex. Increasing the amount of slot flow reduced the size and strength of the nearwall vortices, while increasing the size and strength of the tertiary vortex. Adiabatic endwall temperature measurements revealed higher temperatures surrounding the base of the vane. The endwall measurements also showed that the exit slot flow was effective at cooling only a region of the endwall near the vane leading edge on the suction side. Increasing slot flow was found to have a larger thermal benefit to the endwall relative to increasing combustor liner film-cooling.
Effects of Realistic First-Stage Turbine Endwall Features
Cardwell, Nicholas Don (Virginia Tech, 2005-12-09)
The modern gas turbine engine requires innovative cooling techniques to protect its internal components from the harsh operating environment typically seen downstream of the combustor. Much research has been performed on the design of these cooling techniques thus allowing for combustion temperatures higher than the melting point of the parts within the turbine. As turbine inlet temperatures and efficiencies continue to increase, it becomes vitally important to correctly and realistically model all of the turbine's external cooling features so as to provide the most accurate representation of the associated heat transfer to the metal surfaces. This study examines the effect of several realistic endwall features for a turbine vane endwall. The first study addresses the effects of a mid-passage gap, endwall misalignment, and roughness on endwall film-cooling. The second study focuses on the effect of varying the combustor-to-turbine gap width. Both studies were performed in a large-scale low speed wind tunnel with the same vane geometry. Geometric and flow parameters were varied and the variation in endwall cooling effectiveness was evaluated. Results from these studies show that realistic features, such as surface roughness, can reduce the effectiveness of endwall cooling designs while other realistic features, such as varying the combustor-to-turbine gap width, can significantly improve endwall cooling effectiveness. It was found that, for a given coolant mass flowrate, a narrow combustor-turbine gap width greatly increased the coverage area of the leaked coolant, even increasing adiabatic effectiveness upstream of the vane stagnation point. The turbine designer can also more efficiently utilize leaked coolant from the combustor-to-turbine gap by controlling endwall misalignment, thereby reducing the overall amount of film-cooling needed for the first stage.
Effects of Sand Ingestion on the Cooling of Turbine Blade Outer Air Seals
Land, Camron C. (Virginia Tech, 2006-11-24)
Modern gas turbine engines operate in environments where particle ingestion, especially sand ingestion, can affect the cooling of various turbine parts. The most critical areas are in the combustor and the first stage components of the turbine. Gas temperatures in these areas are the highest compared to other areas and exceed the melting points of the constituent metals. To extend the life of hot section components, internal convective cooling and external film-cooling are required. This study examined the effects of sand ingestion on various cooling geometries. The first part investigated impingement and film-cooling implemented in a double-walled cooling geometry for the purpose of reducing sand size and thereby reducing blockage due to sand ingestion. The second part analyzed the cooling performance of actual turbine blade outer air seals injected with sand. Results from these studies showed areas of impingement that promote particle fragmentation are advantageous in reducing particle size and reducing blockage due to particle ingestion. Blockage was significantly increased based on the percentage of large particles present in the sand samples. Increasing the pressure ratio and decreasing the sand amount were also shown to reduce blockage.
Effects of Sand Ingestion on the Film-Cooling of Turbine Blades
Walsh, William Scott (Virginia Tech, 2005-09-06)
Gas turbine engines for propulsion operate under harsh conditions including gas temperatures that exceed the melting point of the metal, high mechanical stresses, and particulate ingestion such as sand. To maintain a low and uniform metal temperature to extend the life of a turbine component, a complex scheme of internal convective cooling and external film-cooling is required. Gas turbine engines operated in sandy or dusty environments can ingest a large quantity of sand into the mainstream and, more importantly, into the cooling system. Sand ingested into the coolant system has the potential to reduce or block off the flow intended to cool the turbine blades or vanes. If the source of coolant air to a critical region of a turbine blade were partially blocked, it would result in a substantial reduction in component life. This study includes establishing a methodology for testing sand ingestion characteristics on a simulated turbine component with film-cooling holes at room temperature and engine temperatures. The study evaluates a simple array of laser drilled film-cooling holes, similar to a showerhead on the leading edge of an airfoil. The blocking characteristics of this design indicate that increasing the airflow or decreasing the sand amount results in a decreased blockage. It was also determined that as the metal temperature increases, the blockage from a given amount of sand increases. The methodology used in the primary portion of this thesis was modified to test sand ingestion characteristics on actual turbine blades with film-cooling holes at room temperature and engine temperatures. The study evaluated the blockage performance of several different turbine blades including the F-100-229-full, F-100-229-TE, and the F-119 with a new trailing edge cooling methodology know as a microcircuit. It was shown that increasing the airflow or pressure ratio, or decreasing the sand amount would result in decreased blockage. It was also shown that over a certain metal and coolant temperature, the blockage is significantly worsened. However, it was also shown on the F-119 turbine blade that below a given metal temperature, there is no impact of metal or coolant temperature on sand blockage.

Browsing by Author "Thole, Karen A."

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