This paper investigates a theoretical prediction of friction drag reduction in turbulent channel flow which is achieved by using superhydrophobic surfaces. The effect of the hydrophobic surface is considered to be a s...This paper investigates a theoretical prediction of friction drag reduction in turbulent channel flow which is achieved by using superhydrophobic surfaces. The effect of the hydrophobic surface is considered to be a slip boundary condition on the wall, and this new boundary condition is added to Large Eddy Simulation （LES） equations. The predicted drag reduction at Rer= 180 is approximately 30%, which concurs with results obtained from Direct Numerical Simulation （DNS）. An important implication of the present finding is that the near-wall turbulence structures are modified with streamwise slip velocity. In addition, a noticeable effect on the turbulence structure occurs when the slin lenmh is ereater than a certain vahle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
文摘This paper investigates a theoretical prediction of friction drag reduction in turbulent channel flow which is achieved by using superhydrophobic surfaces. The effect of the hydrophobic surface is considered to be a slip boundary condition on the wall, and this new boundary condition is added to Large Eddy Simulation （LES） equations. The predicted drag reduction at Rer= 180 is approximately 30%, which concurs with results obtained from Direct Numerical Simulation （DNS）. An important implication of the present finding is that the near-wall turbulence structures are modified with streamwise slip velocity. In addition, a noticeable effect on the turbulence structure occurs when the slin lenmh is ereater than a certain vahle
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.
