Vortex-induced rotations of two side-by-side square cylinders in a two-dimensional microchannel

This paper studies the self-excited rotations of two side-by-side square cylinders and associated flow structures in a two-dimensional microchannel. As the Reynolds number increases from 5 to 300, the dynamic responses of the square cylinders present five distinct modes: rotation mode (Re = 5), where the pressure force on the cylinder overcomes the shear-induced torque and drives the cylinder rotation; oscillation mode (Re = 25, 50), where both the pressure- and shear-induced torques change periodically with the same period as the rotation angle, which pushes the cylinder oscillation at a certain frequency; static mode (Re = 75), where the pressure and shear forces on the cylinders balance each other and the cylinders are thus self-locked and remain static; random mode (Re = 100, 150, 200), where the complicated flow around the cylinder produces irregular pressure and shear forces on the cylinders, making the cylinders rotate in a random manner; and reversal rotation mode (Re = 300, where the rotation direction of each cylinder is opposite to that at Re = 5), where the shear forces drive the cylinder rotation in the abnormal direction while the irregular pressure makes the instant angular velocity vary randomly. Then, the flow structures are discussed in detail to help understand the interaction mechanisms between the cylinders and fluid flow. The influences of the cylinder dynamics and flow structures on the drag and lift coefficients are revealed.