Self-excited rotation and flow dynamics across a freely rotatable square cylinder confined between two parallel walls

This paper reports on a numerical investigation conducted to study the vortex-induced rotation of a square cylinder confined between two parallel walls. The fluid flow past the cylinder is simulated by solving the Navier-Stokes equations, and the cylinder's motion is captured using Newton's law. A dynamic mesh technique is employed to track the movement of the cylinder boundaries. The numerical model is first validated through comparisons with results in the literature. By changing the fluid velocity and wall distance, the influences of the Reynolds number (40 <= Re <= 800) and blockage ratio (0.10 <= br <= 0.55) on the rotation characteristics and flow dynamics are then revealed. Six distinct rotating modes are recognized in the present confined geometries, namely, static mode I (with theta = 0), static mode II (with theta = +/-pi/4), oscillating mode I (with respect to theta = 0), oscillating mode II (with respect to theta = +/-pi/4), an autorotating mode, and a randomly rotating mode. A phase diagram is made to describe the distribution of these rotating modes with respect to Re and br. To understand the underlying mechanisms, typical fluid-structure interaction details are presented and discussed for each rotating mode. Owing to the confinement of the parallel walls, the shear-induced torque is found to play an important role in the rotation of the cylinder, and its contribution is quantitatively compared with the pressure-induced torque. Published under license by AIP Publishing.