Evaluation of the Cooling Performance for Adjoint Optimized Film Cooling Hole Geometries PDF Download
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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: 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: 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: 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: Humberto A. Zúniga Publisher: ISBN: Category : Gas-turbines Languages : en Pages : 129
Book Description
This suggests that the jets actually have two regions: one region with reduced momentum, ideal for protecting a large area downstream of the point of injection; and another region with more integrity which could withstand more aggressive main flow conditions. A further study should be conducted for this geometry at compound angles with the main flow to test this theory. The studies conducted show that the temperature sensitive paint technique can be used to study the performance of film cooling holes for various geometries. The studies also show the film cooling performance of novel geometries and explain why, in some cases, such new arrangements are desirable, and in others, how they can hurt performance. The studies also point in the direction of further investigations in order to advance cooling technology to more effective applications and reduced coolant consumption, the main goal of applied turbine cooling research.
Author: Katharine Lee Harrison Publisher: ISBN: Category : Languages : en Pages : 314
Book Description
Film cooling computations and experiments were performed to study heat transfer and adiabatic effectiveness for several geometries. Various assumptions commonly made in film cooling experiments were computationally simulated to test the validity of using these assumptions to predict the heat flux into conducting walls. The validity of these assumptions was examined via computational simulations of film cooling on adiabatic, heated, and conducting flat plates using the commercial code FLUENT. The assumptions were found to be reasonable overall, but certain regions in the domain suffered from poor predictions. Film cooling adiabatic effectiveness and heat transfer coefficients for axial holes embedded in a 1 [hole diameter] transverse trench on the suction side of a simulated turbine vane were experimentally investigated as well to determine the net heat flux reduction. Heat transfer coefficients were determined with and without upstream heating both with and without a tripped boundary layer approach flow. The net heat flux reduction for the trench was found to be much higher than for the baseline row of holes. Two transverse trench geometries and a baseline row of holes geometry were also simulated using FLUENT and the results were compared to experiments by Waye and Bogard (2006). Trends between simulated trench configurations and baseline cylindrical holes without a trench were found to be largely in agreement with experimental trends, suggesting that FLUENT can be used as a tool for studying new trench configurations.
Author: Daniel Gutierrez (M.S. in Engineering)
Author: Daniel Gutierrez (M.S. in Engineering)
Author: Emma Veley
Author: Fraser Black Jones (III)
Author: Mulugeta K. Berhe
Author: Mohammad Mahmoud Alshehaby
Author: Humberto A. Zúniga
Author: David Seager
Author: Katharine Lee Harrison
Author: Hessam Babaee
Author: L. Matthews