Evaluation of Additively Manufactured Internal Cooling Channels and Film Cooling Holes for Cooling Effectiveness PDF Download
Are you looking for read ebook online? Search for your book and save it on your Kindle device, PC, phones or tablets. Download Evaluation of Additively Manufactured Internal Cooling Channels and Film Cooling Holes for Cooling Effectiveness PDF full book. Access full book title Evaluation of Additively Manufactured Internal Cooling Channels and Film Cooling Holes for Cooling Effectiveness by Emma Veley. Download full books in PDF and EPUB format.
Author: Emma Veley Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
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.
Author: Emma Veley Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
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.
Author: Curtis Stimpson Publisher: ISBN: Category : Languages : en Pages :
Book Description
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.
Author: Daniel Gutierrez (M.S. in Engineering) Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
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
Author: Paul P. Aghasi Publisher: ISBN: Category : Languages : en Pages : 189
Book Description
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.
Author: Fraser Black Jones (III) Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
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
Author: Thomas Corbett Publisher: ISBN: Category : Languages : en Pages : 0
Book Description
The additive manufacturing (AM) process opens up many opportunities for engineers to explore novel cooling designs that historically may have been costly or even impossible to manufacture. To leverage AM for cooling schemes effectively, engineers must first understand the impact of AM surface roughness on the performance of a variety of internal geometries. The goal of this dissertation was to assess a suite of cooling technologies that were made using AM by comparing the fluid dynamic and heat transfer performance as well as the ability to construct the designs. Specifically, the cooling schemes investigated included wavy channels, pin fin arrays, lattice structures, broken wavy ribs, and diamond pyramid surface features. All of these features were evaluated over a wide range of Reynolds numbers in the turbulent flow regime. The cooling schemes evaluated covered a range of friction factor augmentations from 2 to 500, and heat transfer augmentations between 1.2 and 6 relative to smooth cylindrical channels with no features. The heat transfer and pressure drop of wavy channels was found to be largely a function of the secondary flows with the augmentation scaling as a function of the relative waviness of the channel. Wavy channels were also identified to perform best, in terms of heat transfer, at low Reynolds numbers. Pin fin geometries induced greater heat transfer and pressure loss augmentations than the wavy channels as result of the enhanced surface area and turbulent mixing. Pin shape and spacings were the variables that dictated the pressure loss and heat transfer, though the addition of surface roughness enhanced both flow characteristics. Small surface protrusions such as diamond pyramid turbulators and broken wavy ribs had small performance augmentations relative to the pin fin and wavy channel designs, but these augmentations were found to be insensitive to Reynolds number. The surface features induced substantial near wall mixing with increases in both heat transfer and pressure loss but was further increased as the relative endwall surface roughness increased. Lattice structures had the most significant pressure penalty of all geometries that were considered despite offering only similar heat transfer enhancement to that of the pin fin arrays. Throughout these studies, variations in materials and machines used for the additive manufacturing were identified and related to the performance of internal cooling and pressure loss. These variations led to varying degrees of roughness and a range of surface morphologies. Highly rough wavy channels, for example, significantly increased pressure drop but did not produce an equivalent increase to heat transfer. While arithmetic mean roughness was the primary driver of cooling performance, the surface skewness and kurtosis were found to be key secondary variables. The work presented in this dissertation identified the key flow characteristics and impacts of surface roughness on a variety of internal cooling designs. The data and analyses presented bridge the gap in understanding the performance implications of a range of additively manufactured cooling features empowering designers to integrate new cooling technologies into practical applications.
Author: Luisana Calderon Publisher: ISBN: Category : Languages : en Pages : 71
Book Description
Laser additive manufacturing (LAM) is an emerging technology capable of fabricating complex geometries not possibly made by investment casting methods for gas turbine applications. LAM techniques consist of building parts in a layer-by-layer process by selectively melting metal powders. In the present study, a mock leading edge segment of a turbine blade fabricated by LAM of Inconel 718 powders is investigated. For this particular design, the traditional showerhead film cooling holes have been replaced by two strips containing engineered-porous regions with the purpose of simulating the effect of transpiration cooling.
Author: Ryan Edelson Publisher: ISBN: Category : Languages : en Pages :
Book Description
As hot section gas turbine technology continually improves, it is necessary to fully understand how these technologies impact traditional cooling features. Ceramic matrix composites (CMCs) are a material of great interest in hot section components, as the material's favorable weight and thermal properties at high temperatures have the potential to reduce cooling flows and increase efficiency. However, in order to fully implement this technology, it is critical to understand how the macro scale weave topology affects the fluid dynamics and heat transfer of cooling flows. Particularly, it is of interest to characterize how this weave surface impacts internal convective heat transfer, as well as overall film cooling effectiveness, in order to better predict cooling flow requirements for hot section components made from CMCs. This thesis begins with a study that investigated CMC weave surface topology effects on internal channel pressure loss and heat transfer. Weave surface topology was additively manufactured at three different orientations and used as the walls of an internal channel. Experiments measured bulk pressure loss and heat transfer for a range of Reynolds numbers, while computational fluid dynamics simulations measured bulk and local pressure loss and heat transfer at one specific Reynolds number. Results showed that the weave surface topology increased pressure loss and heat transfer compared to a smooth surface. Additionally, orienting the long weave strands perpendicular to the flow caused greater augmentations than when they were parallel to the flow due to secondary flow vortical structures. As a follow up study, test coupons with film cooling holes relevant to true engine scale were additively manufactured. These test coupons contained weave surfaces, representative of CMCs, on the top wall of the internal coolant supply channel, external film cooled surface or both internal and external surfaces. The coupons were tested over a range of blowing ratios to evaluate the effects of the weave geometry on overall effectiveness, with and without film cooling. Overall effectiveness values without film cooling indicated that the internal CMC coupon with a smooth external surface resulted in significantly increased overall effectiveness levels when compared to the test coupons with an external weave surface. This overall effectiveness increase was because the smooth external surface reduced convective heat transfer between the test coupon and the mainstream flow when compared to an external weave surface. Overall effectiveness results with film cooling showed that increases in blowing ratio caused increases in overall effectiveness for all coupons. Overall effectiveness measurements indicated that the weave surface caused increased mixing between the coolant and mainstream flows compared to a smooth external surface. This increased mixing caused decreased levels of overall effectiveness for coupons with an external weave surface compared to a smooth external surface. The weave surface on the top wall of the internal coolant supply channel increased the heat transfer coefficient of the internal channel and increased in-hole convection when compared to a smooth surface, also increasing levels of overall effectiveness. As such the internal CMC coupon, with a smooth external surface and internal weave surface, saw the highest overall effectiveness levels. This study provided valuable knowledge for turbine designers who wish to implements film cooling into components made of CMC. The results prominently indicated the importance of considering the weave surface topology of the CMC when implementing this new material.
Book Description
This title presents and reflects current active research on various heat transfer topics and related phenomena in gas turbine systems. It begins with a general introduction to gas turbine heat transfer, before moving on to specific areas.
Author: Emily J Sun Publisher: ISBN: Category : Languages : en Pages :
Book Description
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.
Author: Emma Veley
Author: Emma Veley
Author: Curtis Stimpson
Author: Daniel Gutierrez (M.S. in Engineering)
Author: Paul P. Aghasi
Author: Fraser Black Jones (III)
Author: Thomas Corbett
Author: Luisana Calderon
Author: Ryan Edelson
Author: Bengt Sundén
Author: Emily J Sun