CFD Study on Flow Across a Stationary Cylinder in Between Two Counter-Rotating Control Cylinders

Abstract

Flow control by the confined effect of the counter-rotating side/control cylinders (deceleration of the gap-flow), on the free stream flow across a stationary/main cylinder is studied numerically. The study is done for various rotational speeds \( \alpha ( \equiv \omega d/2u_{\infty } ) = 2 - 7 \) and cylinder spacing \( (s/d) = 2 - 5 \) at Reynolds number \( (\text{Re} = u_{\infty } d/\nu ) \) of 100. Various types steady and unsteady flow regimes are reported for the main as well as control cylinder, with increasing rotational velocity of the control cylinder at various cylinder spacing. The results are presented with the help of flow regime map. Unsteady and unsteady flow patterns are demonstrated with the help of streamlines, vorticity contours and wake. Substantial drag reduction is found for the main under the influence of rotating control cylinder; with thrust generation at larger rotational velocity of control cylinder. The flow transitions for the rotating control cylinder of same size is not available in the published literature.