A concept of entropy increment ratio （ s- ） is introduced for compressible turbulence simulation through a series of direct nu- merical simulations （DNS）. s- represents the dissipation rate per unit mechanical ene...A concept of entropy increment ratio （ s- ） is introduced for compressible turbulence simulation through a series of direct nu- merical simulations （DNS）. s- represents the dissipation rate per unit mechanical energy with the benefit of independence of freestream Mach numbers. Based on this feature, we construct the shielding function f, to describe the boundary layer region and propose an entropy-based detached-eddy simulation method （SDES）. This approach follows the spirit of delayed de- tached-eddy simulation （DDES） proposed by Spalart et al. in 2005, but it exhibits much better behavior after their performanc- es are compared in the following flows, namely, pure attached flow with thick boundary layer （a supersonic fiat-plate flow with high Reynolds number）, fully separated flow （the supersonic base flow）, and separated-reattached flow （the supersonic cavity-ramp flow）. The Reynolds-averaged Navier-Stokes （RANS） resolved region is reliably preserved and the modeled stress depletion （MSD） phenomenon which is inherent in DES and DDES is partly alleviated. Moreover, this new hybrid strategy is simple and general, making it applicable to other models related to the boundary layer predictions.展开更多
Herein is introduced the mechanism for active control influencing the generation of the near-wall streamwise vortices,which are closely related to the production of high skin friction in wall-bounded turbulent flows.A...Herein is introduced the mechanism for active control influencing the generation of the near-wall streamwise vortices,which are closely related to the production of high skin friction in wall-bounded turbulent flows.A new opposition control scheme with adjusting control amplitude is proposed and evaluated in turbulent channel flow by direct numerical simulations.The maximum drag reduction rate can be greatly enhanced by the strengthened control.Finally the effectiveness of the control to the coherent structures at high Reynolds numbers is investigated by using a linear transient growth model.展开更多
基金supported by the National Basic Research Program of China(Grant No.2009CB724104)the Innovation Foundation of BUAA for PhD Graduates and the Academic New Artist Award of BUAA for PhD Graduates
文摘A concept of entropy increment ratio （ s- ） is introduced for compressible turbulence simulation through a series of direct nu- merical simulations （DNS）. s- represents the dissipation rate per unit mechanical energy with the benefit of independence of freestream Mach numbers. Based on this feature, we construct the shielding function f, to describe the boundary layer region and propose an entropy-based detached-eddy simulation method （SDES）. This approach follows the spirit of delayed de- tached-eddy simulation （DDES） proposed by Spalart et al. in 2005, but it exhibits much better behavior after their performanc- es are compared in the following flows, namely, pure attached flow with thick boundary layer （a supersonic fiat-plate flow with high Reynolds number）, fully separated flow （the supersonic base flow）, and separated-reattached flow （the supersonic cavity-ramp flow）. The Reynolds-averaged Navier-Stokes （RANS） resolved region is reliably preserved and the modeled stress depletion （MSD） phenomenon which is inherent in DES and DDES is partly alleviated. Moreover, this new hybrid strategy is simple and general, making it applicable to other models related to the boundary layer predictions.
基金Tsupported by the National Natural Science Foundation of China (Grant Nos. 10925210 and 11132005)
文摘Herein is introduced the mechanism for active control influencing the generation of the near-wall streamwise vortices,which are closely related to the production of high skin friction in wall-bounded turbulent flows.A new opposition control scheme with adjusting control amplitude is proposed and evaluated in turbulent channel flow by direct numerical simulations.The maximum drag reduction rate can be greatly enhanced by the strengthened control.Finally the effectiveness of the control to the coherent structures at high Reynolds numbers is investigated by using a linear transient growth model.
