In modern high-load high-pressure turbine,the secondary flow in the blade channel is very strong and occupies a large spanwise region.Although high-quality experimental data at the stage interfaces have been obtained ...In modern high-load high-pressure turbine,the secondary flow in the blade channel is very strong and occupies a large spanwise region.Although high-quality experimental data at the stage interfaces have been obtained in previous research,the influence of the clocking position on the secondary flow patterns is not fully understood.This paper investigates the clocking effect in a 1.5-stage high-pressure turbine and focuses on the variations of secondary flow patterns and their effect on the turbine performance.The detailed flow fields of various clocking positions were obtained by carrying out unsteady flow simulations using an in-house code.Among the four clocking positions in this work,the highest entropy generation was observed when the wakes from stator 1 hit the leading edges of stator 2,which is opposite to the well-known conclusion for the turbine with high-aspect-ratio blades.Detailed flow analysis showed that the wakes and the near tip secondary vortices from stator 1 showed different traces when entering the stator 2 channel and the secondary vortices clearly have a more important influence in determining the performance.The different behaviors of the secondary vortices explained the performance variations due to the clocking effect.展开更多
This paper presents a novel model for flow angles at off-design conditions.The model is based on energy conservation in turbomachinery.By the mean of average process,statistical properties of the wake profile are rela...This paper presents a novel model for flow angles at off-design conditions.The model is based on energy conservation in turbomachinery.By the mean of average process,statistical properties of the wake profile are related to the flow angle and mainstream parameters;then by adopting the classic flow topology of behind-blade wakes,the effect of operating conditions is included in the plot and a model for flow angle is thus developed.The advantage of the model is that it can achieve off-design flow angle estimations with design flow characteristics and it is compatible with CFD-based throughflow methods.This model is then implemented into a standard CFD-based throughflow solver from the previous research to estimate off-design characteristics of blade rows with proper input-output strategies.Furthermore,the effect of loss upon flow angle is also modeled as corrections to the proposed model.The model is validated on a compressor stage and the results show promising accuracy for off-design flow angle estimations.展开更多
Efficient method to handle the geometric constraints in the optimization of turbomachinery blade profile is required. Without constraints on the blade thickness, optimal designs typically yield thinner blade to reduce...Efficient method to handle the geometric constraints in the optimization of turbomachinery blade profile is required. Without constraints on the blade thickness, optimal designs typically yield thinner blade to reduce the friction loss, however, at the risk of degraded strength and stiffness. This issue is seldom discussed and existing literature always treat the blade thickness constraint in an indirect manner. In this work, two different geometric constraints on the blade thickness are proposed and applied in the adjoint optimization: one is on the maximum blade thickness and the other is on the blade area. Methods to compute sensitivities of both constraints are proposed and they are integrated into an optimization system based on a finite volume code and a solver for the discrete adjoint equation. Adjoint optimization is conducted to minimize the entropy production in a transonic compressor stage. Results for the adjoint optimization without geometry constraint and two comparative cases are detailed. It is indicated that three cases yield similar performance improvement;however, if geometry constraints are properly handled, the optimal designs have almost the same maximum thickness as the original design, compared to a thinner blade profile with 14% reduction of maximum thickness in the case without geometry constraint. The cases considering geometry constraints also consume slightly reduced Central Processing Unit(CPU) cost. Result of this work verifies the effectiveness of the proposed method to treat geometric constraints in adjoint optimization.展开更多
This paper presents a novel approach of modeling the air-cooled turbine with CFD-based throughflow analysis. Starting from the basic equations of motion, governing equations and source terms for mass, momentum and ene...This paper presents a novel approach of modeling the air-cooled turbine with CFD-based throughflow analysis. Starting from the basic equations of motion, governing equations and source terms for mass, momentum and energy are formulated in an analytical manner. These source terms are to mimic the authentic injection-mainstream interactions with easy implementation. The source terms in the aero-cooling scenario are related to corresponding sources in the aerodynamic-only analysis. Based on such formulations, a novel strategy is developed to estimate aerodynamic characteristics of a blade row under film cooling with known characteristics under no cooling. The model and the strategy are validated in the classic NASA E3 turbine guide vane under various operating conditions. Sensitivity studies of input parameters are conducted to evaluate the applicability of the proposed model. Specifically, the flow rate distributions of cooling flow at different cooling holes are crucial for accurate predictions.展开更多
The turbulence characteristics of the shaped hole film cooling are very complex.In this study,Large Eddy Simulation(LES)and Reynolds-averaged Navier-Stokes(RANS)are used to study the film cooling of the shaped hole.Th...The turbulence characteristics of the shaped hole film cooling are very complex.In this study,Large Eddy Simulation(LES)and Reynolds-averaged Navier-Stokes(RANS)are used to study the film cooling of the shaped hole.The time-averaged results are compared with the experimental data in the literature.Because of the eddy-viscosity model,the RANS method roughly deals with the simulation of boundary layer,which leads to a large deviation.The RANS results are compared with the LES results to identify the weaknesses of the Realizable k-e model in predicting the turbulence characteristics of the shaped hole film cooling.The eddy viscosity hypothesis and the temperature gradient diffusion hypothesis are evaluated using LES data.Furthermore,the turbulence characteristics of the in-hole flow are analysed with the help of the incremental Proper Orthogonal Decomposition(iPOD).The turbulence presents strong anisotropy and some convection structures are induced from the shear zone.展开更多
With the relative movement of neighboring blade rows,flows in multi-stage turbomachinery are unsteady and periodic in time at the design condition.As an alternative to the widely used time domain time marching method,...With the relative movement of neighboring blade rows,flows in multi-stage turbomachinery are unsteady and periodic in time at the design condition.As an alternative to the widely used time domain time marching method,the harmonic balance(HB)method has been successfully applied to simulate the essentially unsteady flow of multi-stage turbomachinery.By modelling various number of harmonics,the accuracy of this method could be adjusted at different level of computational cost.In this article,accuracy of the harmonic balance method is not only validated against the time domain time marching method,as in most previous works on this topic,but also against the data from an experiment campaign of a two-stage high-pressure turbine where strong tip leakage flow exists.Efficiency of this method is also assessed in detail by adjusting the number of harmonics and comparing with time domain time marching solution results.Results show that the harmonic balance method is a flexible tool with adjustable accuracy for fast-turnaround unsteady flow simulation of multi-stage turbomachinery.Results from this work can provide a guidance in applying the harmonic balance method with balance between accuracy and computational cost.展开更多
Interaction between the coolant and the secondary flow plays an important role in endwall cooling performance.For the leading-edge region,oncoming main flow inside the boundary layer impinges onto the vane leading edg...Interaction between the coolant and the secondary flow plays an important role in endwall cooling performance.For the leading-edge region,oncoming main flow inside the boundary layer impinges onto the vane leading edge and turns into the horseshoe vortex.Horseshoe vortex entrains coolant off the surface,thus posing severe challenges to the cooling design there.Based on analyses on the leading-edge vortex formation mechanism,a new kind of endwall film cooling design,vertical hole upstream of the saddle point,is proposed to obtain more uniform film coverage over the vane/endwall junction region.Coolant injected from the vertical hole can pass over the horseshoe vortex and impinge around the stagnation line on the vane leading edge.Uniform film coverage can be obtained around the vane leading edge where coolant clings to the endwall surface due to the span-wise pressure gradient of the stagnation region.Numerical simulations are conducted about the cooling performance of two main kinds of both isotropic and anisotropic hole geometries for the endwall and vane surface.Results come that the anisotropic hole shows significant advantages over the isotropic one because it suppresses the symmetrical kidney vortices thus weakening the mixture with high-temperature gas.Blowing ratio(M)effect is analyzed and conclusions are drawn that the cooling performance of the endwall around the leading edge is sensitive to M and adiabatic film cooling effectiveness peaks at about M=2.0.Better cooling performance over the vane corner region can be obtained when M gets even higher while the effective film coverage area shrinks.Apart from that,the phenomenon of phantom cooling on the upper triangular region of the suction surface can be observed when coolant on the endwall is entrained by the vortex formed at the corner of the leading edge.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51876098)。
文摘In modern high-load high-pressure turbine,the secondary flow in the blade channel is very strong and occupies a large spanwise region.Although high-quality experimental data at the stage interfaces have been obtained in previous research,the influence of the clocking position on the secondary flow patterns is not fully understood.This paper investigates the clocking effect in a 1.5-stage high-pressure turbine and focuses on the variations of secondary flow patterns and their effect on the turbine performance.The detailed flow fields of various clocking positions were obtained by carrying out unsteady flow simulations using an in-house code.Among the four clocking positions in this work,the highest entropy generation was observed when the wakes from stator 1 hit the leading edges of stator 2,which is opposite to the well-known conclusion for the turbine with high-aspect-ratio blades.Detailed flow analysis showed that the wakes and the near tip secondary vortices from stator 1 showed different traces when entering the stator 2 channel and the secondary vortices clearly have a more important influence in determining the performance.The different behaviors of the secondary vortices explained the performance variations due to the clocking effect.
基金funded through the National Science and Technology Major Project(2017-Ⅲ-0009-0035)National Natural Science Foundation of China(Grant No.52276031)。
文摘This paper presents a novel model for flow angles at off-design conditions.The model is based on energy conservation in turbomachinery.By the mean of average process,statistical properties of the wake profile are related to the flow angle and mainstream parameters;then by adopting the classic flow topology of behind-blade wakes,the effect of operating conditions is included in the plot and a model for flow angle is thus developed.The advantage of the model is that it can achieve off-design flow angle estimations with design flow characteristics and it is compatible with CFD-based throughflow methods.This model is then implemented into a standard CFD-based throughflow solver from the previous research to estimate off-design characteristics of blade rows with proper input-output strategies.Furthermore,the effect of loss upon flow angle is also modeled as corrections to the proposed model.The model is validated on a compressor stage and the results show promising accuracy for off-design flow angle estimations.
基金financially supported by National Natural Science Foundation of China, under project No. 51876098 and No. 51506107
文摘Efficient method to handle the geometric constraints in the optimization of turbomachinery blade profile is required. Without constraints on the blade thickness, optimal designs typically yield thinner blade to reduce the friction loss, however, at the risk of degraded strength and stiffness. This issue is seldom discussed and existing literature always treat the blade thickness constraint in an indirect manner. In this work, two different geometric constraints on the blade thickness are proposed and applied in the adjoint optimization: one is on the maximum blade thickness and the other is on the blade area. Methods to compute sensitivities of both constraints are proposed and they are integrated into an optimization system based on a finite volume code and a solver for the discrete adjoint equation. Adjoint optimization is conducted to minimize the entropy production in a transonic compressor stage. Results for the adjoint optimization without geometry constraint and two comparative cases are detailed. It is indicated that three cases yield similar performance improvement;however, if geometry constraints are properly handled, the optimal designs have almost the same maximum thickness as the original design, compared to a thinner blade profile with 14% reduction of maximum thickness in the case without geometry constraint. The cases considering geometry constraints also consume slightly reduced Central Processing Unit(CPU) cost. Result of this work verifies the effectiveness of the proposed method to treat geometric constraints in adjoint optimization.
基金funded by the National Natural Science Foundation of China (Project 51876098)the National Natural Science Foundation of China (Project 51911540475)the National Science and Technology Major Project (2017-Ⅲ-0009-0035)。
文摘This paper presents a novel approach of modeling the air-cooled turbine with CFD-based throughflow analysis. Starting from the basic equations of motion, governing equations and source terms for mass, momentum and energy are formulated in an analytical manner. These source terms are to mimic the authentic injection-mainstream interactions with easy implementation. The source terms in the aero-cooling scenario are related to corresponding sources in the aerodynamic-only analysis. Based on such formulations, a novel strategy is developed to estimate aerodynamic characteristics of a blade row under film cooling with known characteristics under no cooling. The model and the strategy are validated in the classic NASA E3 turbine guide vane under various operating conditions. Sensitivity studies of input parameters are conducted to evaluate the applicability of the proposed model. Specifically, the flow rate distributions of cooling flow at different cooling holes are crucial for accurate predictions.
基金This study is supported by the National Natural Science Foundation of China(Project Grant No.51876098)National Science and Technology Major Project(J2019-III-0007-0050)This research is also sponsored by the Open Fund from Science and Technology on Thermal Energy and Power Laboratory(TPL2018B05).
文摘The turbulence characteristics of the shaped hole film cooling are very complex.In this study,Large Eddy Simulation(LES)and Reynolds-averaged Navier-Stokes(RANS)are used to study the film cooling of the shaped hole.The time-averaged results are compared with the experimental data in the literature.Because of the eddy-viscosity model,the RANS method roughly deals with the simulation of boundary layer,which leads to a large deviation.The RANS results are compared with the LES results to identify the weaknesses of the Realizable k-e model in predicting the turbulence characteristics of the shaped hole film cooling.The eddy viscosity hypothesis and the temperature gradient diffusion hypothesis are evaluated using LES data.Furthermore,the turbulence characteristics of the in-hole flow are analysed with the help of the incremental Proper Orthogonal Decomposition(iPOD).The turbulence presents strong anisotropy and some convection structures are induced from the shear zone.
基金This work is supported by National Natural Science Foundation of China under project No.51876098the grant from the Hubei Provincial Natural Science Foundation of China No.2018CFB317.
文摘With the relative movement of neighboring blade rows,flows in multi-stage turbomachinery are unsteady and periodic in time at the design condition.As an alternative to the widely used time domain time marching method,the harmonic balance(HB)method has been successfully applied to simulate the essentially unsteady flow of multi-stage turbomachinery.By modelling various number of harmonics,the accuracy of this method could be adjusted at different level of computational cost.In this article,accuracy of the harmonic balance method is not only validated against the time domain time marching method,as in most previous works on this topic,but also against the data from an experiment campaign of a two-stage high-pressure turbine where strong tip leakage flow exists.Efficiency of this method is also assessed in detail by adjusting the number of harmonics and comparing with time domain time marching solution results.Results show that the harmonic balance method is a flexible tool with adjustable accuracy for fast-turnaround unsteady flow simulation of multi-stage turbomachinery.Results from this work can provide a guidance in applying the harmonic balance method with balance between accuracy and computational cost.
基金supported by the National Natural Science Foundation of China(Grant No.51876098)National Science and Technology Major Project(2017-Ⅲ-0009-0035)sponsored by the Tsinghua University Initiative Scientific Research Program。
文摘Interaction between the coolant and the secondary flow plays an important role in endwall cooling performance.For the leading-edge region,oncoming main flow inside the boundary layer impinges onto the vane leading edge and turns into the horseshoe vortex.Horseshoe vortex entrains coolant off the surface,thus posing severe challenges to the cooling design there.Based on analyses on the leading-edge vortex formation mechanism,a new kind of endwall film cooling design,vertical hole upstream of the saddle point,is proposed to obtain more uniform film coverage over the vane/endwall junction region.Coolant injected from the vertical hole can pass over the horseshoe vortex and impinge around the stagnation line on the vane leading edge.Uniform film coverage can be obtained around the vane leading edge where coolant clings to the endwall surface due to the span-wise pressure gradient of the stagnation region.Numerical simulations are conducted about the cooling performance of two main kinds of both isotropic and anisotropic hole geometries for the endwall and vane surface.Results come that the anisotropic hole shows significant advantages over the isotropic one because it suppresses the symmetrical kidney vortices thus weakening the mixture with high-temperature gas.Blowing ratio(M)effect is analyzed and conclusions are drawn that the cooling performance of the endwall around the leading edge is sensitive to M and adiabatic film cooling effectiveness peaks at about M=2.0.Better cooling performance over the vane corner region can be obtained when M gets even higher while the effective film coverage area shrinks.Apart from that,the phenomenon of phantom cooling on the upper triangular region of the suction surface can be observed when coolant on the endwall is entrained by the vortex formed at the corner of the leading edge.
