Download or read book Investigation of Inlet and Diffuser Geometry Modifications on Film Cooling Performance of Additively Manufactured Shaped Holes in Crossflow written by Fraser Black Jones (III) and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Film cooling holes permit gas turbine firing temperatures to significantly exceed the melting point of the constituent materials by venting compressor bleed air along the surface of a component forming a buffer between the wall and surrounding gas. A film cooling hole is a passive geometric feature with performance entirely derived from the holes geometry and the operating conditions of the coolant and mainstream. Significant effort has been made to characterize a wide variety of hole geometries but no method has been put forth to determine the optimal hole geometry for a given local flow field and component. Even for traditional, subtractive machined holes this would be a daunting task, but the difficulty grows exponentially as additive manufacturing (AM) permits greater design freedom to the thermal engineer. Presented here is a validated method for determining the optimal film cooling hole geometry of both traditionally or additively manufactured components using computationally inexpensive RANS CFD. Additionally, beyond just validating existing designs, this method can generate novel designs which leverage additive manufacturings unique design space to significantly enhance performance beyond what is possible with traditionally machined holes. While this method has many limitations inherited from RANS, which we will explore in depth, it has proven robust and effective at calculating performance in any coolant/mainstream flowfield. This work stands unique in film cooling literature but will hopefully be superseded by improved methods still to come. Realizable K-epsilon RANS is validated and found to be robust in predicting the flow field of film cooling holes. This information is used to investigate the flow inside of holes where traditional experimental methods are severely restricted. Key separation regions at the inlet and diffuser are identified to be severely detrimental to film cooling performance. CFD was used to predict geometries that would improve hole performance leveraging the unique design freedoms of additive manufacturing. This resulted in large performance gains as predicted by the RANS. Furthermore, as the gross separation regions within the hole were improved, the RANS predictions of surface temperature were found to be increasingly reliably. CFD was employed to search for better performing traditional and AM diffuser designs, the best of which were verified experimentally to significantly improve performance as predicted. Finally, adjoint optimization was used to fully optimize the hole geometry yielding further improvements in performance which were again experimentally validated

Download or read book Evaluation of Additively Manufactured Internal Cooling Channels and Film Cooling Holes for Cooling Effectiveness written by Emma Veley and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cooling of the high-pressure turbine in a gas turbine engine is essential for durability because the gas temperature entering the turbine exceeds the melting point of the hardware. Both internal and external cooling reduces the temperature of the blades and vanes. Using air that bypassed the combustor as coolant, the convective heat transfer from the hardware to this internal coolant is often augmented by ribs or a serpentine path. To cool the external surface, coolant passes through holes on the outer wall of airfoil. The coolant creates a protective film on the surface. The shape of the cooling hole influences the cooling effectiveness of this film cooling. Additive manufacturing facilitates rapid prototyping compared to traditional manufacturing methods, which can be exploited for designing and evaluating cooling schemes of gas turbine hardware. The work in this dissertation used additive manufacturing to investigate the cooling performance of several internal and external cooling schemes manufactured in at engine scale for the unique objective of determining the impacts of the internal cooling scheme on the external cooling. A variety of cooling hole shapes were investigated for this work: cylindrical hoes, meter-diffuser shaped holes, and novel optimized holes. Once additively manufactured, the as-built cooling hole surfaces were analyzed to determined their roughness and minimum cross-sectional areas. The arithmetic mean roughness of holes built at the optimal build orientation (perpendicular to the build plate) were on the order of 10 [mu]m; whereas those investigated at other build orientations had roughness values up to 75 [mu]m. For the holes built perpendicular to the substrate the minimum cross-sectional area was usually greater than the design intent but within 15%. The additive process also created an overbuilt lip on the leading edge (windward) side of the hole exit for these holes because of the thin wall thickness in the design. Using these cooling holes, the impact of rounding on meter-diffuser shaped holes and optimized holes on overall effectiveness was investigated. The rounding, which came in the form of inlet fillets on the meter-diffuser shaped holes, was found to decrease the required pressure ratio to obtain the same cooling effectiveness. The deviations from the design due to the additive process caused the novel cooling hole shapes designed through adjoint optimization to perform differently than anticipated. For example, the coolant jet from hole designed for co-flow did not bifurcate as the computational simulation showed. The cross-flow optimized hole outperformed the co-flow optimized hole for most of the tested blowing ratio when both holes were tested in a co-flow configuration. These results from the novel optimized holes proved the necessity of experimentally verifying new designs prior to incorporating into final cooling schemes. The effect of supply channel height, number of channels, ribs, and the cross-sectional shape of the supply channel was investigated to determine the impact of each on the overall effectiveness. Designs that had high overall effectiveness from only internal cooling had less augmentation in effectiveness from film cooling than designs with less effective internal cooling. For example, a ribbed channel typically had a lower film-cooling augmentation than the film-cooling augmentation for same supply channel without ribs. However, a highly effective feed channel can obtain a higher overall effectiveness without any film cooling than a poorly performing feed channel can obtain with film cooling. But the features that create a highly effective feed channel can also cause the cooling jet to lift-off the surface and mix with the hot gas path, which was seen with some rib and hole combinations and with the triangle -- vertex down supply channels. Therefore, the hole shape, the supply channel geometry, and the junction between the two all significantly contribute to a cooling scheme's performance and all three must be considered concurrently to create an optimal cooling design.

Download or read book Evaluation of the Cooling Performance for Adjoint Optimized Film Cooling Hole Geometries written by Daniel Gutierrez (M.S. in Engineering) and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Advancement in additive manufacturing (AM) methods along with the application to gas turbine component manufacturing has expanded the feasibility of creating complex hole geometries to be used in gas turbines. The design possibilities for new hole geometries have become unlimited as these improved AM methods allow for the creation of holes with complex hole geometries such as rounded inlets, protrusions in the surface of the inlet and outlet of holes, among others. This advancement in such technology has sparked interest among turbine research groups for the design and creation of optimized versions of holes that showcase sophisticated geometries, which would otherwise not be possible to be manufactured using conventional manufacturing methods. Recently, a computational adjoint based optimization method by a past student in our lab (Fraser B. Jones) was used to design shaped film cooling holes fed by internal co-flow and cross-flow channels. The CFD simulations for said hole geometries predicted that the holes optimized for use with cross-flow (X-AOpt) and co-flow (Co-AOpt) would significantly increase adiabatic effectiveness. However, only the X-AOpt hole was tested experimentally in this previous study. In this study, adiabatic and matched Biot number models were built for 5X engine scale models of the X-AOpt and Co-AOpt shaped holes and tested experimentally in a low speed wind tunnel facility. The optimized shaped holes are experimentally evaluated using measurements of adiabatic effectiveness and overall cooling effectiveness. Coolant was fed to the holes with an internal co-flow channel and tested at various blowing ratios (M=0.5-4). For reference, experiments were also conducted with 5X engine scale models for the baseline 7-7-7 sharp inlet (SI) shaped hole, and a 15-15-1 rounded inlet (RI) shaped hole (shown in a previous parametric optimization study by Jones to be the optimum expansion angles for a shaped hole). Discharge coefficient, C [subscript d], measurements for the Co-AOpt geometry are analyzed in greater detail and compared against the other hole geometries tested for the study. In addition, computational predictions of C [subscript d] for a 15-15-1 RI hole will be compared against experimental measurements from this study. Results from the experiments performed at the low speed facility for 5X scale models confirmed that the X-AOpt hole had a 75% increase in adiabatic effectiveness compared to the 7-7-7 SI shaped hole. However, the Co-AOpt hole had only a 30% increase in adiabatic effectiveness, which is substantially less than had been computationally predicted

Download or read book Experiments and Simulation of Shaped Film Cooling Holes Fed by Crossflow with Rib Turbulators written by Dale Wilson Fox (III) and published by . This book was released on 2018 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt: Most studies of turbine airfoil film cooling in laboratories have used relatively large plenums to feed flow into the coolant holes. A more realistic inlet condition for the film cooling holes is an internal crossflow channel. In this study, angled rib turbulators were installed in two geometric configurations inside the internal crossflow channel, at 45° and 135°, to assess the impact on film cooling effectiveness. Film cooling hole inlets positioned in both pre-rib and post-rib locations tested the effect of hole inlet position relative to the rib turbulators. Experiments were performed varying channel velocity ratio and jet to mainstream velocity ratio. These results were compared to the film cooling performance of previously measured shaped holes fed by a smooth internal channel, as well as RANS simulations performed for select cases. The film cooling hole discharge coefficients and channel friction factors were measured for both rib configurations. Spatially-averaged film cooling effectiveness behaves similarly to holes fed by a smooth internal crossflow channel, but hole-to-hole variation due to the obstruction by the ribs was observed.

Download or read book Cooling Performance of Additively Manufactured Microchannels and Film Cooling Holes written by Curtis Stimpson and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Additive manufacturing (AM) enables fabrication of components that cannot be made with any other manufacturing method. Significant advances in metal-based AM systems have made this technology feasible for building production parts to be used use in commercial products. In particular, the gas turbine industry benefits from AM as a manufacturing technique especially for development of components subjected to high heat flux. It has been shown that the use of microchannels in high heat flux components can lead to more efficient cooling designs than those that presently exist. The current manufacturing methods have prevented the use of microchannels in such parts, but AM now makes them manufacturable. However, before such designs can become a reality, much research must be done to characterize impacts on flow and heat transfer of AM parts. The current study considers the effect on flow and heat transfer through turbine cooling features made with AM. Specifically, the performance of microchannels and film cooling holes made with laser powder bed fusion (L-PBF) is assessed.A number of test coupons containing microchannels were built from high temperature alloy powders on a commercially available L-PBF machine. Pressure drop and heat transfer experiments characterized the flow losses and convective heat transfer of air passing through the channels at various Reynolds numbers and Mach numbers. The roughness of the channels surfaces was characterized in terms of statistical roughness parameters; the morphology of the roughness was examined qualitatively. Magnitude and morphology of surface roughness found on AM parts is unlike any form of roughness seen in the literature. It was found that the high levels of roughness on AM surfaces result in markedly augmented pressure loss and heat transfer at all Reynolds numbers, and conventional flow and heat transfer correlations produce erroneous estimates. The physical roughness measurements made in this study were correlated to flow and heat transfer measurements to generate a predictive model for flow through AM microchannels. The flow compressibility was also found to play a significant role in flow loss through these channels.Overall effectiveness of film cooling combined with the internal microchannel flow was examined in a conjugate experimental setup. The validity of the experimental conditions was established by matching important dimensionless parameters of the experimental setup to common values found in turbine engines. These results showed that the roughness in the film cooling holes produced higher in-hole convection than those made with current manufacturing methods. The roughness in the holes also repressed the film performance. However, high relative roughness was shown to minimize the impact of coolant feed direction on the film effectiveness of the AM holes.

Download or read book Dependence of Film Cooling Effectiveness on 3D Printed Cooling Holes written by Paul P. Aghasi and published by . This book was released on 2016 with total page 189 pages. Available in PDF, EPUB and Kindle. Book excerpt: To investigate the viability of using additive manufacturing technology for flat plate film cooling experiments a new experiential facility was constructed using gas analysis and oxygen sensitive paint as a method of measuring and characterizing film cooling effectiveness for various additive manufacturing technologies as well as aluminum. The ultimate objective of this work is to assess whether these technologies can be a replacement for traditional aluminum CNC machining. Film Cooling Effectiveness is closely dependent on the geometry of the hole emitting the cooling film. These holes are sometimes quite expensive to machine by traditional methods so 3D printed test pieces have the potential to greatly reduce the cost of film cooling tests. What is unknown is the degree to which parameters like layer resolution and the choice of 3D printing technologies influence the results of a film cooling test. A new flat-plate film cooling facility employing the mass transfer analogy (introduction of foreign gas as coolant, not to be confused with the sublimation method) and measurements both by gas sample analysis and oxygen-sensitive paint is first validated using gas analysis and oxygen sensitive paint cross correlation. The same facility is then used to characterize the film cooling effectiveness of a diffuser shaped film cooling hole geometry. These diffuser holes (film hole diameter, D of 0.1 inches) are then produced by a variety of different manufacturing technologies, including traditional machined aluminum, Fused Deposition Modeling (FDM), Stereo Lithography Apparatus (SLA) and PolyJet with layer thicknesses from 0.001D (25 [micro]m) to 0.12D (300 [micro]m). Tests are carried out at mainstream flow Mach number of 0.30 and blowing ratios from 1.0 to 3.5. The coolant gas used is CO2 yielding a density ratio of 1.5. Surface quality is characterized by an Optical Microscope that calculates surface roughness. Test coupons with rougher surface topology generally showed delayed film hole blow off and higher film cooling effectiveness at increased blowing ratios compared to the geometries with lower measured surface roughness.

Download or read book Diffused exit Film Cooling Holes Fed by an Internal Crossflow written by John W. McClintic and published by . This book was released on 2017 with total page 434 pages. Available in PDF, EPUB and Kindle. Book excerpt: Film cooling is an essential technology to the operation of modern gas turbine engines, allowing for greater efficiency and part durability. Due to film cooling’s complexity, laboratory studies of film cooling isolate various effects by intentionally simplifying or neglecting various aspects of the film cooling problem. One such aspect that had been consistently neglected by film cooling studies is how the internal flow within the turbine blade affects film cooling performance. Studies have found that feeding the holes with an internal crossflow, directed perpendicular to the mainstream flow, can cause up to a 50% reduction in film cooling effectiveness. This result is of concern because internal crossflow is a common internal flow condition in gas turbine engines. However, none of the former studies have made a concerted effort to examine the important scaling parameters governing this effect. Nor have they provided experimental evidence showing the cause of this reduction in effectiveness due to internal crossflow. In this study, a wide range of flow conditions was studied for two common film cooling hole geometry types: axial and compound angle diffused-exit film cooling holes. Internal crossflow-to-mainstream velocity ratios of VR [subscript c] = 0.2-0.6 were tested along with jet-to-mainstream velocity ratios of VR = 0.2-1.7. Film cooling effectiveness and discharge coefficients were measured for this full range of flow conditions for both geometries in order to produce a sufficiently large data set to observe important trends in the data. It was found that the discharge coefficients, centerline effectiveness, and centerline location all scaled with the crossflow-to-jet velocity ratio, VR [subscript i] for the axial holes. Temperature and velocity fields showed that VR [subscript i] also scaled the in-hole temperature and velocity fields. A swirling flow within the hole was shown to cause ingestion of mainstream into the diffused exit of the hole and biasing of the issuing jet in the outlet diffuser, which reduced film cooling effectiveness. The direction of bias at the exit resulted from the direction of the internal crossflow and was critical for compound angle holes. Crossflow directed counter to the lateral direction of coolant injection caused improved film cooling effectiveness relative to the in-line crossflow direction

Download or read book Influence of In Hole Roughness and High Freestream Turbulence on Film Cooling From a Shaped Hole written by Robert Schroeder and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Gas turbines are heavily used for electricity generation and aircraft propulsion with a strong desire in both uses to maximize thermal efficiency while maintaining reasonable power output. As a consequence, gas turbines run at high turbine inlet temperatures that require sophisticated cooling technologies to ensure survival of turbine components. One such technology is film cooling with shaped holes, where air is withdrawn from latter stages of the compressor, is bypassed around the combustor, and is eventually ejected out holes in turbine component surfaces. Air ejected from these shaped holes helps maintain components at temperatures lower than flow from the combustor. Many studies have investigated different factors that influence shaped hole performance. However, no studies in open literature have investigated how cooling performance is affected by roughness along interior walls of the shaped hole. The effect of in-hole roughness on shaped hole film cooling was the focus of this research. Investigation of in-hole roughness effects first required the determination of behavior for a shaped hole with smooth walls. A public shaped hole, now used by other investigators as well, was designed with a diffused outlet having 7 degree expansion angles and an area ratio of 2.5. At low freestream turbulence intensity of 0.5%, film cooling adiabatic effectiveness for this smooth hole was found to peak at a blowing ratio of 1.5. Measurements of flowfields and thermal fields revealed causes of this behavior. Blowing ratio increases above 1.5 caused the jet from the smooth hole to penetrate higher into the surrounding mainstream, exhibit a stronger counter-rotating vortex pair, and have narrower contact with the wall than at lower blowing ratios. Experiments performed at high freestream turbulence intensity of 13% revealed dynamics of how freestream turbulence both diluted and laterally spread coolant. At the high blowing ratio of 3 the dilution and spreading were competing effects, such that elevated freestream turbulence did not cause a decrease in area-averaged effectiveness. At the blowing ratio of 1.5, high freestream turbulence caused area-averaged effectiveness to decrease 17% relative to the low freestream turbulence case. Film cooling performance was measured for the shaped hole geometry with several different configurations of in-hole roughness. At low freestream turbulence intensity, in-hole roughness caused decreases in area-averaged adiabatic effectiveness up to 61% relative to the smooth hole performance. These percent decreases in adiabatic effectiveness were more severe with increasing roughness levels and with increasing blowing ratios. Flowfield and thermal field measurements for the configuration with largest roughness size showed that the decrease in adiabatic effectiveness for rough holes as compared to smooth holes was due to thicker boundary layers along the interior walls of the cooling holes. The thicker boundary layers resulted in faster jet core flow, which in turn caused increased penetration of coolant into the mainstream and increased turbulence intensity inside the jet, with both leading to reduced adiabatic effectiveness. Detrimental effects of in-hole roughness persisted at the high freestream turbulence conditions as well.

Download or read book Shaped Hole Effects on Film Cooling Effectiveness and a Comparison of Multiple Effectiveness Measurement Techniques written by Trent Alan Varvel and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This experimental study consists of two parts. For the first part, the film cooling effectiveness for a single row of seven cylindrical holes with a compound angle is measured on a flat surface using five different measurement techniques: steady-state liquid crystal thermography, transient liquid crystal thermography, pressure sensitive paint (PSP), thermocouples, and infrared thermography. A comparison of the film cooling effectiveness from each of the measurement techniques is presented. All methods show a good comparison, especially for the higher blowing ratios. The PSP technique shows the most accurate measurements and has more advantages for measuring film cooling effectiveness. Also, the effect of blowing ratio on the film cooling effectiveness is investigated for each of the measurement techniques. The second part of the study investigates the effect of hole geometries on the film cooling effectiveness using pressure sensitive paint. Nitrogen is injected as the coolant air so that the oxygen concentration levels can be obtained for the test surface. The film effectiveness is then obtained by the mass transfer analogy. Five total hole geometries are tested: fan-shaped laidback with a compound angle, fan-shaped laidback with a simple angle, a conical configuration with a compound angle, a conical configuration with a simple angle, and the reference geometry (cylindrical holes) used in part one. The effect of blowing ratio on film cooling effectiveness is presented for each hole geometry. The spanwise averaged effectiveness for each geometry is also presented to compare the geometry effect on film cooling effectiveness. The geometry of the holes has little effect on the effectiveness at low blowing ratios. The laterally expanded holes show improved effectiveness at higher blowing ratios. All experiments are performed in a low speed wind tunnel with a mainstream velocity of 34 m/s. The coolant air is injected through the coolant holes at four different coolant-to-mainstream velocity ratios: 0.3, 0.6, 1.2, and 1.8.

Download or read book Flow Visualization of Discrete hole Film Cooling with Spanwise Injection Over a Cylinder written by Louis M. Russell and published by . This book was released on 1979 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Effects of Hole Length Supply Plenum Geometry and Freestream Turbulence on Film Cooling Performance written by and published by . This book was released on 2000 with total page 324 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book HEAT TRANSFER EFFECTS OF NON TRADITIONAL FILM COOLING HOLE GEOMETRIES ON COOLING EFFECTIVENESS written by Emily J Sun and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A gas turbine is a device that harnesses energy from the manipulation of air. In pursuit of greater efficiencies, the temperatures of the combustors are being increased. Given these conditions, certain design steps and materials selection are vital for the performance of the components. On the design side, internal and external cooling features can be designed to control the heat transfer to and from a part. Film cooling is a mechanism by which some of the internal cooling flow is allowed to flow over the surface of the airfoil of a turbine blade via holes in the wall of the turbine blade. Currently film cooling hole geometry designs are usually drilled through the walls of the airfoil through laser drilling or electro discharge machining (EDM). With this method of creating the film cooling holes, the designs for these holes needs to fall along a linear axis and tool-paths must be considered. However, with the development of additive manufacturing, turbine blades can be constructed with film cooling holes already embedded in the designs. As a result, the designs for film cooling holes have a greater complexity tolerance, which can be used to optimize the internal fluid dynamics. In order to explore the effects of the complex film cooling geometries, various film cooling hole geometries have been designed. The major designs were different modification of the 7-7-7 hole. The two types of design modifications were to the cross section or the curvature of the meter. The four major designs were: the Square hole, the Half Circle hole, the 60 Turn hole, and the 90 Turn hole. An experiment was conducted to determine the effect of the different changes on film cooling effectiveness in comparison to the 7-7-7 hole.

Download or read book Experimental and Computational Studies of Film Cooling with Compound Angle Injection written by and published by . This book was released on 1995 with total page 31 pages. Available in PDF, EPUB and Kindle. Book excerpt: The thermal efficiency of gas turbine systems depends largely on the turbine inlet temperature. Recent decades have seen a steady rise in the inlet temperature and a resulting reduction in fuel consumption. At the same time, it has been necessary to employ intensive cooling of the hot components. Among various cooling methods, film cooling has become a standard method for cooling of the turbine airfoils and combustion chamber walls. The University of Minnesota program is a combined experimental and computational study of various film-cooling configurations. Whereas a large number of parameters influence film cooling processes, this research focuses on compound angle injection through a single row and through two rows of holes. Later work will investigate the values of contoured hole designs. An appreciation of the advantages of compound angle injection has risen recently with the demand for more effective cooling and with improved understanding of the flow; this project should continue to further this understanding. Approaches being applied include: (1) a new measurement system that extends the mass/heat transfer analogy to obtain both local film cooling and local mass (heat) transfer results in a single system, (2) direct measurement of three-dimensional turbulent transport in a highly-disturbed flow, (3) the use of compound angle and shaped holes to optimize film cooling performance, and (4) an exploration of anisotropy corrections to turbulence modeling of film cooling jets.

Download or read book The Effect of Channel Parameters on the Adiabatic Film Cooling Effectiveness of Shaped Holes in Crossflow written by Ellen Katherine Wilkes and published by . This book was released on 2015 with total page 168 pages. Available in PDF, EPUB and Kindle. Book excerpt: There is limited information in the literature on the behavior of shaped film cooling holes fed by crossflow and even less information on the effect of crossflow parameters on film cooling performance. Here, two scaled film cooling models were used to independently vary the crossflow Reynolds numbers in the range of 36,000 to 57,000 and the crossflow velocity ratio from 0.36 to 0.64. Careful attention was paid to controlling physical parameters between comparisons to isolate the effects of internal velocity ratio or Reynolds number on the performance of shaped holes. In the process of controlling the physical parameters of the system, a novel correction for coolant to mainstream density ratio was proposed. The results of this study showed that channel velocity ratio had a larger effect on the film cooling performance of shaped holes than channel Reynolds number. When the mass flux of fluid through the film cooling holes was at the highest and lowest value, increasing the channel velocity ratio decreased the film cooling effectiveness. At a middle mass flux, the outcome was opposite such that an increase in channel velocity ratio resulted in increased effectiveness.

Download or read book An Experimental Investigation on the Effects of Film Cooling Hole Geometry written by David Seager and published by . This book was released on 1998 with total page 228 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Investigation of Approach Flow Parameters Scaling Factors and Measurement Accuracy for Film Cooling Effectiveness and Heat Transfer Coefficient Measurements written by Joshua Brian Anderson and published by . This book was released on 2017 with total page 572 pages. Available in PDF, EPUB and Kindle. Book excerpt: Film cooling is widely used in gas turbine engines to manage temperatures within the hot section of the engine. In this work, several investigations are described, all of which studied how fundamental hydrodynamic and thermal parameters influence the performance of film cooling. The first investigation studied the impact of freestream turbulence, boundary layer thickness, Reynolds number, and Mach number on film cooling performance, using axial shaped film cooling holes. The second study considered a similar set of parameters, and investigated their impact on compound-angle oriented film cooling holes. Both of these studies utilized measurements of adiabatic effectiveness and heat transfer coefficient augmentation. In general, the parameters had effects which were dependent on the coolant flow rate and density ratio. The final study considered methods to reduce the experimental uncertainty which arises from conduction and radiation errors in thermal measurements. A careful evaluation of the thermal boundary layer was used to validate these corrections

Download or read book Investigation of Film Cooling Effectiveness and Enhancement of Cooling Performance written by Sangkwon Na and published by . This book was released on 2006 with total page 382 pages. Available in PDF, EPUB and Kindle. Book excerpt: Advanced gas turbines are designed to operate at increasingly higher inlet temperatures to increase efficiency and specific power output. This increase in the operating temperature is enabled by advances in high-temperature resistant materials such as super alloys and thermal-barrier coatings (TBCs) and by the development of effective cooling methods that lower the temperature of all surfaces that come in contact with the hot gases. Since the lower-temperature air used for cooling is extracted from the compressor, efficiency considerations demand effective cooling with minimum cooling flow. This study focuses on film cooling with a twofold objective. The first is to examine the effects of TBC blockage and surface roughness on film-cooling effectiveness. The second objective is to explore, develop, and evaluate more efficient film-cooling methods. This study is accomplished by using second-order accurate computational fluid dynamics (CFD) analyses of the "compressible" Navier-Stokes equations in which the details of the film-cooling geometry and relevant flow features are resolved. To ensure that the solutions generated are meaningful, a grid-sensitivity study was performed for each configuration examined. Also, a validation study was performed to assess the turbulence models used.