Channel-confined flow-induced rotation of an asymmetrically confined square cylinder in a two-dimensional laminar flow regime

This study focuses on the flow-induced rotational characteristics of an asymmetrically confined square cylinder in a channel for various engineering applications. We consider the classical, fully developed channel flow problem to numerically study the flow-induced rotation (FIR) of a square cylinder in a two-dimensional laminar flow regime. We employ our in-house computational fluid dynamics solver, based on the hybrid Lagrangian-Eulerian method, for the present study. For the very first time, we identify seven distinct rotational modes by investigating FIR for a wide range of Reynolds number Re ( 1 - 150 ) and eccentricity epsilon (0, 1/3, 2/3). This paper reports the combined effects of Re and epsilon on the FIR characteristics in terms of rotational modes, accompanying flow structures, and pertinent engineering parameters. At low Re, the shear-induced torque dominates over the pressure-induced torque, whereas with an increase in Re, the pressure-induced torque gradually outweighs the shear-induced torque. Thus, we observe a smooth transition in the direction of rotation from clockwise to counterclockwise with increasing Re. This study involves a detailed discussion of the flow physics and moment-generating mechanisms for four intriguing rotational modes, including Autorotation, Mono-harmonic Oscillation, Bi-harmonic Oscillation, and Reversal Autorotation. The current study has applications in micro energy-harvesting, vortex generation, and microfluidic mixing.