Influence of flexible fins on vortex-induced load over a circular cylinder at low Reynolds number

Abstract

Fins or fairings are typically streamlined structures employed to reduce the vortex-induced unsteady forces acting on a bluff body by preventing shear layer roll-up in the near-wake region. In this work, fins would refer to thin plate-like structures attached tangentially to the bluff body's top and bottom surfaces. Of particular interest here are flexible fins that can undergo static deformation or coupled fluid-elastic vibrations due to the non-linear interactions with the shear layer from a circular cylinder and the roll-up of shear layers at the trailing edge of the fin. We present a numerical analysis to realize the effect of fin flexibility on the performance with regard to vortex-induced forces by varying non-dimensional flexural rigidity, KB∈ [0.01, 10], of the fins. Two-dimensional simulations are carried out for a fixed non-dimensional fin mass ratio, m*=0.1, and Reynolds number, Re = 100. In this study, we consider two fins attached tangentially to the top and bottom surfaces of a fixed circular cylinder. We show that as the flexibility of the fins increases progressively, the stability of the fins is lost and the fins undergo a coupled flapping motion. As a function of KB, three distinct dynamic response regimes of the flexible fins are identified: (i) fixed-point stability for KB>1, (ii) periodic outward flapping 0.025≤KB≤0.1, and (iii) periodic flapping about the initial position with large amplitudes KB<0.025. Flexibility and inclination angle of fins are observed to be effective in minimizing the vortex-induced forces.