Influence of two near-wall cylinders with different angles on flow structure in transitional flow

In order to investigate the influence of the two near-wall cylinders with different angles on the flow structure in transitional flow,this model based on the cylinder diameter D = 15 mm with Reynolds number 300 was calculated. Flow visualization experiments with the particle image velocimetry（ PIV） system were conducted based on the open-loop fluid test bench. The results show that when Re number is 300,the angle γ of the two near-wall cylinders has a significant effect on the flow structure around the cylinder. The upstream cylindrical wake is suppressed with the increase of the angle γ,where the upper side is suppressed and then the lower side is suppressed and the acceleration effect of the upstream near-wall region first increases and then decreases. The downstream cylindrical wake is mainly affected from the upstream shear layer to the downstream shear layer with the increase of the angle γ． Also,the magnitude and regions of the acceleration effect increase and then stabilize in the nearwall area. The influence of the angle γ on the flow structure is gradually increased and the disturbance in the near-wall area is gradually enhanced within the cases of γ＜7.6°． The influence of the angle γ on the flow structure is gradually weakened and the range of fluid disturbance tends to be stable within the cases of γ＞7.6°． The transient flow characteristics were analyzed in detail for the case of γ =-7.6°． It is found that the periodic vortex shedding phenomenon is formed in the wake of two near-wall cylinders,which enhances the flow instability of the wall.