The instability of a flexible filament immersed in uniform flow is studied.A numerical simulation based on the immersed boundary method is conducted on a two-dimensional uniform flow past a flapping filament.Different...The instability of a flexible filament immersed in uniform flow is studied.A numerical simulation based on the immersed boundary method is conducted on a two-dimensional uniform flow past a flapping filament.Different from the conventional bistability behavior,more regions of initial states of filament corresponding to different modes of motion are partitioned at each freestream velocity,and a new stable mode of motion with smaller flapping amplitude is observed.Mode selection highly depends on these initial states.展开更多
The transient response of the turbulent enstrophy transport to opposition control in the turbulent channel flow is studied with the aid of direct numerical simulation. It is found that the streamwise enstrophy and the...The transient response of the turbulent enstrophy transport to opposition control in the turbulent channel flow is studied with the aid of direct numerical simulation. It is found that the streamwise enstrophy and the spanwise enstrophy are suppressed by the attenuation of the stretching terms at first, while the vertical enstrophy is reduced by inhibiting the tilt of the mean shear. In the initial period of the control, the streamwise enstrophy evolves much slower than the other two components. The vertical vorticity component exhibits a rapid monotonic decrease and also plays an important role in the attenuation of the other two components.展开更多
基金Supported by the Fundamental Research Funds for the Central Universitiesthe National Natural Science Foundation of China-NSAF under Grant No 10976029.
文摘The instability of a flexible filament immersed in uniform flow is studied.A numerical simulation based on the immersed boundary method is conducted on a two-dimensional uniform flow past a flapping filament.Different from the conventional bistability behavior,more regions of initial states of filament corresponding to different modes of motion are partitioned at each freestream velocity,and a new stable mode of motion with smaller flapping amplitude is observed.Mode selection highly depends on these initial states.
基金supported by the National Natural Science Foundation of China (Nos.10925210,11002081,and 11132005)
文摘The transient response of the turbulent enstrophy transport to opposition control in the turbulent channel flow is studied with the aid of direct numerical simulation. It is found that the streamwise enstrophy and the spanwise enstrophy are suppressed by the attenuation of the stretching terms at first, while the vertical enstrophy is reduced by inhibiting the tilt of the mean shear. In the initial period of the control, the streamwise enstrophy evolves much slower than the other two components. The vertical vorticity component exhibits a rapid monotonic decrease and also plays an important role in the attenuation of the other two components.
