As a universal principle of turbulence cascade,scaling law is important in the research on statistics of turbulence.In the thesis PIV system is used to measure the streamwise velocity vector(u') and the component ...As a universal principle of turbulence cascade,scaling law is important in the research on statistics of turbulence.In the thesis PIV system is used to measure the streamwise velocity vector(u') and the component of vorti-city (dv'/dx) in order to analyze the parameters of SL scaling law in the boundary layer at Reθ=2694 (Reθ is obtained by the momentum thickness and free flow velocity).The method of wavelet and statistics are used in this paper.Then,the parameters of SL scaling law are fitted with the scaling law of extended self similarity,extended of refined similarity hypothesis and a new form of refined similarity.At different distances from the wall and different scale,the results show that the fitted curves of u' is in accordance with experimental curves.For dv'/dx,the fitted curves which are fitted with extended of refined similarity hypothesis and a new form of refined similarity is in accordance with experimental curves.展开更多
Based on Reynolds-averaged Navier-Stokes approach,a laminar-turbulence transition model is proposed in this study that takes into account the effects of different instability modes associated with the variations in Ma...Based on Reynolds-averaged Navier-Stokes approach,a laminar-turbulence transition model is proposed in this study that takes into account the effects of different instability modes associated with the variations in Mach numbers of compressible boundary layer flows.The model is based on k-ω-γ three-equation eddy-viscosity concept with k representing the fluctuating kinetic energy,ωthe specific dissipation rate and the intermittency factorγ.The particular features of the model are that:1)k includes the non-turbulent,as well as turbulent fluctuations;2)a transport equation for the intermittency factorγis proposed here with a source term set to trigger the transition onset;3)through the introduction of a new length scale normal to wall,the present model employs the local variables only avoiding the use of the integral parameters,like the boundary layer thicknessδ,which are often cost-ineffective with the modern CFD(Computational Fluid Dynamics)methods;4)in the fully turbulent region,the model retreats to the well-known k-ωSST(Shear Stress Transport)model.This model is validated with a number of available experiments on boundary layer transitions including the incompressible,supersonic and hypersonic flows past flat plates,straight/flared cones at zero incidences,etc.It is demonstrated that the present model can be successfully applied to the engineering calculations of a variety of aerodynamic flow transition.展开更多
A modified transition model is given based on the shear stress transport (SST) turbulence model and an intermittency transport equation. The energy gradient term in the original model is replaced by flow strain rate t...A modified transition model is given based on the shear stress transport (SST) turbulence model and an intermittency transport equation. The energy gradient term in the original model is replaced by flow strain rate to saving computational costs. The model employs local variables only, and then it can be conveniently implemented in modern computational fluid dynamics codes. The fifth-order weighted compact nonlinear scheme and the fourth-order staggered scheme are applied to discrete the governing equations for the purpose of minimizing discretization errors, so as to mitigate the confusion between numerical errors and transition model errors. The high-order package is compared with a second-order TVD method on simulating the transitional flow of a flat plate. Numerical results indicate that the high-order package give better grid convergence property than that of the second-order method. Validation of the transition model is performed for transitional flows ranging from low speed to hypersonic speed.展开更多
基金Sponsored by the Key Laboratory of Mechanics on Western Disaster and Environment of the Ministry of Education of China
文摘As a universal principle of turbulence cascade,scaling law is important in the research on statistics of turbulence.In the thesis PIV system is used to measure the streamwise velocity vector(u') and the component of vorti-city (dv'/dx) in order to analyze the parameters of SL scaling law in the boundary layer at Reθ=2694 (Reθ is obtained by the momentum thickness and free flow velocity).The method of wavelet and statistics are used in this paper.Then,the parameters of SL scaling law are fitted with the scaling law of extended self similarity,extended of refined similarity hypothesis and a new form of refined similarity.At different distances from the wall and different scale,the results show that the fitted curves of u' is in accordance with experimental curves.For dv'/dx,the fitted curves which are fitted with extended of refined similarity hypothesis and a new form of refined similarity is in accordance with experimental curves.
基金Supported by the National Natural Science Foundation of China(Grant Nos.10232020 and 90505005)
文摘Based on Reynolds-averaged Navier-Stokes approach,a laminar-turbulence transition model is proposed in this study that takes into account the effects of different instability modes associated with the variations in Mach numbers of compressible boundary layer flows.The model is based on k-ω-γ three-equation eddy-viscosity concept with k representing the fluctuating kinetic energy,ωthe specific dissipation rate and the intermittency factorγ.The particular features of the model are that:1)k includes the non-turbulent,as well as turbulent fluctuations;2)a transport equation for the intermittency factorγis proposed here with a source term set to trigger the transition onset;3)through the introduction of a new length scale normal to wall,the present model employs the local variables only avoiding the use of the integral parameters,like the boundary layer thicknessδ,which are often cost-ineffective with the modern CFD(Computational Fluid Dynamics)methods;4)in the fully turbulent region,the model retreats to the well-known k-ωSST(Shear Stress Transport)model.This model is validated with a number of available experiments on boundary layer transitions including the incompressible,supersonic and hypersonic flows past flat plates,straight/flared cones at zero incidences,etc.It is demonstrated that the present model can be successfully applied to the engineering calculations of a variety of aerodynamic flow transition.
基金supported by the National Basic Research Program of China (Grant No. 2009CB723800)the National Natural Science Foundation of China (Grand No. 11072259)
文摘A modified transition model is given based on the shear stress transport (SST) turbulence model and an intermittency transport equation. The energy gradient term in the original model is replaced by flow strain rate to saving computational costs. The model employs local variables only, and then it can be conveniently implemented in modern computational fluid dynamics codes. The fifth-order weighted compact nonlinear scheme and the fourth-order staggered scheme are applied to discrete the governing equations for the purpose of minimizing discretization errors, so as to mitigate the confusion between numerical errors and transition model errors. The high-order package is compared with a second-order TVD method on simulating the transitional flow of a flat plate. Numerical results indicate that the high-order package give better grid convergence property than that of the second-order method. Validation of the transition model is performed for transitional flows ranging from low speed to hypersonic speed.
