Wake suppression of a cylinder immersed in turbulence using rotating rods

Abstract

In this study, we conducted three-dimensional direct numerical simulations to investigate the control performance of the free-stream turbulence past a circular cylinder with two small rotating rods at Re = 3900. In the case A and case B, two control rods with different rotating ratio α are positioned symmetrically at the circumferential angle θ=±45° and θ=±120° from the forward stagnation point of the main cylinder, respectively. Here, α is the ratio of the tangential velocity of the control rod surface ur to the inflow velocity U∞. Compared to the bare cylinder immersed in turbulence, both installation positions of the rotating rods at α = 2 result in a significant suppression on the wake flow. Specifically, the time-averaged drag coefficient Cd¯ was reduced by 25%, and the root mean square value of the lift coefficient measured to reduce by up to 30%. Statistical analysis is then performed, in terms of the Reynolds stresses, mean field, and the turbulent wake visualization to show variations in the flow dynamics. As expected, the front-mounted control rods inject kinetic energy into the boundary layer, effectively suppressing the turbulence fluctuations on both sides of the main cylinder. The work done by viscous forces around the rotating control rods and the suppression of turbulent fluctuations contribute to the pressure recovery observed in the rear-mounted control rod case. Proper orthogonal decomposition method is further employed to analyze the key features of the controlled wake of two cases with α = 2.