Symmetry Breaking of a Rigid-Flexible Coupling System at Low Reynolds Numbers

Abstract

Abstract Flow past a rigid-flexible coupling system consisting of a rigid plate and a trailing closed flexible filament was simulated numerically. An immersed boundary method was developed based on OpenFOAM to solve this fluid-structure interaction (FSI) problem. Three simulations including flow past a rigid circular cylinder, a rigid plate, and two flexible loops were conducted to validate our code. The motion modes transition and dynamic performance of the coupling system were investigated at low Reynolds numbers (Re ≤ 80), where the tension coefficient and bending coefficient of the filament were fixed. According to the symmetry of the filament motion, six motion modes have been identified for different filament lengths and Reynolds numbers, i.e. symmetric and stationary (SS) mode, asymmetric and stationary (AS) mode, regular and unilateral flap (RUF) mode, transition motion (TM) mode, symmetric and bilateral flap (SBF) mode, and asymmetric and bilateral flap (ABF) mode. Moreover, symmetry breaking was discovered in the AS, RUF, and ABF modes. The positions of the filament at different times were drawn to describe its movement and distinguish motion modes. Meanwhile, the drag and lift of the coupling system were investigated and a significant drag reduction was found. In addition, The time-averaged lift directly depended on the symmetry of the filament and rapidly changed with a sudden alteration in symmetry. Our research is helpful to understand the change of motion behavior of this coupling system at low Reynolds numbers.