The Passive Control Strategy For The Flow Past Square Cylinder

In practical engineering,the flow around a bluff body has been the focus problem.It is significant and has important theoretical value to understand the characteristics of the flow and relevant the coefficient through numerical simulation.According to different flow states,we adopt several kinds of passive control methods to reduce the flow drag around the square cylinder and weaken the wake turbulence.In laminar flow,Computational Fluid Dynamics is used to investigate the features of flow the square cylinder with a couple of parallel detached flat plates or a perforated plate in different case.In unsteady turbulence state,the characteristics of flowing past a three-dimensional square cylinder with a flexible plate are studied by using fluid–structure interaction.We use different methods to reduce the flow drag around the square cylinder and make the wake stable.The present numerical results show that it can be concluded that the features can be changed when two parallel plates are added at the behind of square cylinder.In the certain distance of the two plates,Karman Vortex street is guided to road between the two plates.On the one hand,vortex shedding onset is delayed.On the other hand,critical Reynolds number and the drag force of the square cylinder are reduced in some extent due to the addition of the detached plates.The characteristic coefficient of square cylinder,such as the rms of lift coefficient and St are reduced.When the two plates are added,the pressure differential between the front and rear region of square cylinder is decreased and then the drag is decreased.The most significant effect is obtained when S/D=2.0,Re=150.Compared with the single square cylinder,the drag coefficient of square cylinder with two plates distance of 2.0D is increased by 15.45%.When a perforated plate is located behind of the square cylinder,it's found that the recirculation zone augments with the increase of L/D,the vortex trace on the upper and lower of the square cylinder moves gradually backwards until a stable recirculation zone forming between the square cylinder and a perforated plate.The large vortex that has been formed can be broken into small vortexes owing to the perforated plate.The most significant effect is obtained when L~P/D=2.0,Re=150.Compared with the single square cylinder,the drag coefficient of square cylinder with fences at the place of L~P =2.0D is increased by 31.33%.For high Reynolds numbers,Using the method of Fluid-solid coupling,we set up a flexible plate at the behind of square cylinder.The vortex shedding can be effectively suppressed and the flow pattern can be changed by putting a flexible plate at the back of the square cylinder.Compared with the case of a single square cylinder,the drag coefficient can be reduced by 34.6%,the RMS of the lift coefficient can be reduced by 84.8% and then flow pulsation is reduced and at the same time St is reduced by 79.5%.