Direct numerical simulation of the wake adjustment and hydrodynamic characteristics of a circular cylinder symmetrically attached with fin-shaped strips

Abstract

This work has numerically studied the effects of the coverage ratio and angular position of a pair of fin-shaped strips on the hydrodynamic forces and wake structures of a circular cylinder at both low and medium Reynolds numbers (Re = 60–500) using direct numerical simulation (DNS). The coverage ratio varies from 0.11 to 0.22, corresponding to the coverage angle (β) of a strip from 20° to 40°. The angular position (θ), measured from the forward stagnation point to the front edge of strips, ranges from 30° to 120° with increment of 30°. The numerical results indicate that the hydrodynamic coefficients are sensitive to the coverage and placement angles of the strips. The fluid forces are reduced with the introduction of a couple of 20°-fin-shaped strips, while they are amplified by placing 30°-fin-shaped strips or 40°-fin-shaped strips in the front surface of cylinder. The amplification/suppression is associated with the development of boundary layer and the wake structure, embodied in the length of recirculation bubble, the wake width, the tripping and reattachment of boundary layer as well as the separation point. By placing a pair of 40°-fin-shaped strips at θ = 60°, the time-mean drag and the lift fluctuation at Re = 180 are increased by 38.7% and 97.7%, respectively. For the cylinder equipped with 30°-fin-shaped strips at θ = 30°, the three-dimensional mode A and mode B wake structures are observed at medium Re = 200–500.