The influence of drag-reducing superhydrophobic(SHPo)surface on turbulent boundary layer(TBL)is investigated.A large area of the SHPo surface(about 10δ99 in the streamwise and 5δ99 in the spanwise)is fabricated to f...The influence of drag-reducing superhydrophobic(SHPo)surface on turbulent boundary layer(TBL)is investigated.A large area of the SHPo surface(about 10δ99 in the streamwise and 5δ99 in the spanwise)is fabricated to fully evolve the coherent structures in the TBL.A comparative experiment is carried out by time-resolved particle image velocimetry on a smooth surface and the SHPo surface at Re_(τ)=528.Velocity profiles with high spatial resolution are obtained by the single-pixel resolution ensemble correlation method.The reduction of the streamwise velocity gradient is observed in the near-wall region of y<0.05δ99 on the SHPo surface.By comparing the turbulence statistics,it is discovered that the Reynolds shear stress is reduced by 15.7%,and the turbulent kinetic energy is reduced by 12.3%on the SHPo surface.The coherent structures are investigated by the snapshot proper orthogonal decomposition(POD)and conditional average method.The intensity of Q_(2)/Q_(4)events on the SHPo surface has declined by 16.1%and 12.7%,respectively.The number of clockwise spanwise vortices is substantially reduced by 47%.Through spatial two-point correlation analysis,the streamwise and wall-normal direction scales of the coherent structures on the SHPo surface are suppressed.展开更多
基金the National Natural Science Foundation of China(Grant Nos.11732010,11972251,11872272,11902218,and 12172242)the Ministry of Industry and Information Technology(Grant No.[2019]360).
文摘The influence of drag-reducing superhydrophobic(SHPo)surface on turbulent boundary layer(TBL)is investigated.A large area of the SHPo surface(about 10δ99 in the streamwise and 5δ99 in the spanwise)is fabricated to fully evolve the coherent structures in the TBL.A comparative experiment is carried out by time-resolved particle image velocimetry on a smooth surface and the SHPo surface at Re_(τ)=528.Velocity profiles with high spatial resolution are obtained by the single-pixel resolution ensemble correlation method.The reduction of the streamwise velocity gradient is observed in the near-wall region of y<0.05δ99 on the SHPo surface.By comparing the turbulence statistics,it is discovered that the Reynolds shear stress is reduced by 15.7%,and the turbulent kinetic energy is reduced by 12.3%on the SHPo surface.The coherent structures are investigated by the snapshot proper orthogonal decomposition(POD)and conditional average method.The intensity of Q_(2)/Q_(4)events on the SHPo surface has declined by 16.1%and 12.7%,respectively.The number of clockwise spanwise vortices is substantially reduced by 47%.Through spatial two-point correlation analysis,the streamwise and wall-normal direction scales of the coherent structures on the SHPo surface are suppressed.
