In order to investigate the aerodynamics of a high speed low pressure turbine works in high Mach number and low Reynold number environment,the effect of freestream turbulence(FST)on the boundary layer development on t...In order to investigate the aerodynamics of a high speed low pressure turbine works in high Mach number and low Reynold number environment,the effect of freestream turbulence(FST)on the boundary layer development on the high speed low pressure turbine under different Reynolds numbers(Re)is numerically investigated.Large eddy simulation is adopted here with a subgrid scale model of Wall Adapting Local Eddy viscosity(WALE).Cases with Re ranging from 100000 to 400000 under an exit Mach number(Ma)of 0.87 have been considered at low and high FST levels.A low Ma case(0.17)under very low Re has also been studied under both low and high FST.It is found that higher Re or FST level leads to earlier transition.Re has a greater effect than FST on the development of boundary layer.The effect of FST on the boundary layer depends on the Re.The boundary layer development shows totally different behaviors under different Ma.A separation bubble could be formed under low Ma while no attachment could be detected under high Ma.The FST has a stronger effect on the separated boundary layer under low Ma,which could eliminate the separation in the present study.For all the cases under low FST,the Kelvin-Helmholtz instability is the dominate mechanism in the transition process.For the low Ma case with high FST,the streamwise streaks play a dominant role in the transition process.For the high Ma cases with high FST,both the streamwise streaks and Kelvin-Helmholtz instability work in the transition process.The streamwise streaks play a more important role when the Re increased.展开更多
A comprehensive methodology for simulating 2 D dynamic stall at fluctuating freestream is proposed in this paper.2 D CFD simulation of a SC1095 airfoil exposed to a fluctuating freestream of Mach number 0.537±0.2...A comprehensive methodology for simulating 2 D dynamic stall at fluctuating freestream is proposed in this paper.2 D CFD simulation of a SC1095 airfoil exposed to a fluctuating freestream of Mach number 0.537±0.205 and Reynolds number 6.1×10~6(based on the mean Mach number)and undergoing a 10°±10°pitch oscillation with a frequency of 4.25 Hz was conducted.These conditions were selected to be representative of the flow experienced by a helicopter rotor airfoil section in a real-life fast forward flight.Both constant freestream dynamic stall as well as fluctuating freestream dynamic stall simulations were conducted and compared.The methodology was carefully validated with experimental data for both transonic flow and dynamic stall under fluctuating freestream.Overall,the results suggest that the fluctuating freestream alters the dynamic stall mechanism documented for constant freestream in a major way,emphasizing that inclusion of this effect in the prediction of dynamic stall related rotor loads is imperative for rotor performance analysis and blades design.展开更多
For flow simulations with complex geometries and structured grids,it is preferred for high-order difference schemes to achieve high accuracy.In order to achieve this goal,the satisfaction of free-stream preservation i...For flow simulations with complex geometries and structured grids,it is preferred for high-order difference schemes to achieve high accuracy.In order to achieve this goal,the satisfaction of free-stream preservation is necessary to reduce the numerical error in the numerical evaluation of grid metrics.For the linear upwind schemes with flux splitting the free-stream preserving property has been achieved in the early study[Q.Li et al.,Commun.Comput.Phys.,22(2017),pp.64–94].In the current paper,new series of nonlinear upwind-biased schemes through WENO interpolation will be proposed.In the new nonlinear schemes,the shock-capturing capability on distorted grids is achieved,which is unavailable for the aforementioned linear upwind schemes.By the inclusion of fluxes on the midpoints,the nonlinearity in the scheme is obtained through WENO interpolations,and the upwind-biased construction is acquired by choosing relevant grid stencils.New third-and fifth-order nonlinear schemes are developed and tested.Discussions are made among proposed schemes,alternative formulations of WENO and hybrid WCNS,in which a general formulation of center scheme with midpoint and nodes employed is obtained as a byproduct.Through the numerical tests,the proposed schemes can achieve the designed orders of accuracy and free-stream preservation property.In 1-D Sod and Shu-Osher problems,the results are consistent with the theoretical predictions.In 2-D cases,the vortex preservation,supersonic inviscid flow around cylinder at M¥=4,Riemann problem,and shock-vortex interaction problems have been tested.More specifically,two types of grids are employed,i.e.,the uniform/smooth grids and the randomized/locally-randomized grids.All schemes can get satisfactory results in uniform/smooth grids.On the randomized grids,most schemes have accomplished computations with reasonable accuracy,except the failure of one third-order scheme in Riemann problem and shock-vortex interaction.Overall,the proposed nonlinear schemes have the capability to solve flow problems on badly deformed grids,and the schemes can be used in the engineering applications.展开更多
基金supported by the National Science and Technology Major Project of China (No. 2017-Ⅱ-0008-0022,2019-Ⅱ-008-0028)
文摘In order to investigate the aerodynamics of a high speed low pressure turbine works in high Mach number and low Reynold number environment,the effect of freestream turbulence(FST)on the boundary layer development on the high speed low pressure turbine under different Reynolds numbers(Re)is numerically investigated.Large eddy simulation is adopted here with a subgrid scale model of Wall Adapting Local Eddy viscosity(WALE).Cases with Re ranging from 100000 to 400000 under an exit Mach number(Ma)of 0.87 have been considered at low and high FST levels.A low Ma case(0.17)under very low Re has also been studied under both low and high FST.It is found that higher Re or FST level leads to earlier transition.Re has a greater effect than FST on the development of boundary layer.The effect of FST on the boundary layer depends on the Re.The boundary layer development shows totally different behaviors under different Ma.A separation bubble could be formed under low Ma while no attachment could be detected under high Ma.The FST has a stronger effect on the separated boundary layer under low Ma,which could eliminate the separation in the present study.For all the cases under low FST,the Kelvin-Helmholtz instability is the dominate mechanism in the transition process.For the low Ma case with high FST,the streamwise streaks play a dominant role in the transition process.For the high Ma cases with high FST,both the streamwise streaks and Kelvin-Helmholtz instability work in the transition process.The streamwise streaks play a more important role when the Re increased.
文摘A comprehensive methodology for simulating 2 D dynamic stall at fluctuating freestream is proposed in this paper.2 D CFD simulation of a SC1095 airfoil exposed to a fluctuating freestream of Mach number 0.537±0.205 and Reynolds number 6.1×10~6(based on the mean Mach number)and undergoing a 10°±10°pitch oscillation with a frequency of 4.25 Hz was conducted.These conditions were selected to be representative of the flow experienced by a helicopter rotor airfoil section in a real-life fast forward flight.Both constant freestream dynamic stall as well as fluctuating freestream dynamic stall simulations were conducted and compared.The methodology was carefully validated with experimental data for both transonic flow and dynamic stall under fluctuating freestream.Overall,the results suggest that the fluctuating freestream alters the dynamic stall mechanism documented for constant freestream in a major way,emphasizing that inclusion of this effect in the prediction of dynamic stall related rotor loads is imperative for rotor performance analysis and blades design.
基金sponsored by the project of National Numerical Wind-tunnel of China under the grant number No.NNW2019ZT4-B12The second author thanks for the support of National Natural Science Foundation of China under the Grant No.11802324The corresponding author thanks for the contribution of Dr.Qilong Guo on the incipient 1-D computations,and he is also grateful to Prof.Kun Xu for his efforts on the revision of the manuscript as well as Dr.Pengxin Liu for supplementary computations.
文摘For flow simulations with complex geometries and structured grids,it is preferred for high-order difference schemes to achieve high accuracy.In order to achieve this goal,the satisfaction of free-stream preservation is necessary to reduce the numerical error in the numerical evaluation of grid metrics.For the linear upwind schemes with flux splitting the free-stream preserving property has been achieved in the early study[Q.Li et al.,Commun.Comput.Phys.,22(2017),pp.64–94].In the current paper,new series of nonlinear upwind-biased schemes through WENO interpolation will be proposed.In the new nonlinear schemes,the shock-capturing capability on distorted grids is achieved,which is unavailable for the aforementioned linear upwind schemes.By the inclusion of fluxes on the midpoints,the nonlinearity in the scheme is obtained through WENO interpolations,and the upwind-biased construction is acquired by choosing relevant grid stencils.New third-and fifth-order nonlinear schemes are developed and tested.Discussions are made among proposed schemes,alternative formulations of WENO and hybrid WCNS,in which a general formulation of center scheme with midpoint and nodes employed is obtained as a byproduct.Through the numerical tests,the proposed schemes can achieve the designed orders of accuracy and free-stream preservation property.In 1-D Sod and Shu-Osher problems,the results are consistent with the theoretical predictions.In 2-D cases,the vortex preservation,supersonic inviscid flow around cylinder at M¥=4,Riemann problem,and shock-vortex interaction problems have been tested.More specifically,two types of grids are employed,i.e.,the uniform/smooth grids and the randomized/locally-randomized grids.All schemes can get satisfactory results in uniform/smooth grids.On the randomized grids,most schemes have accomplished computations with reasonable accuracy,except the failure of one third-order scheme in Riemann problem and shock-vortex interaction.Overall,the proposed nonlinear schemes have the capability to solve flow problems on badly deformed grids,and the schemes can be used in the engineering applications.
