Numerical study of blockage effects on aerodynamic characteristics of an oscillating rectangular cylinder

Abstract

Abstract The flow around a stationary and oscillating square cylinder was numerically simulated at various blockage ratios in order to study the effects of wall confinement on the aerodynamic characteristics of the cylinder. Numerical methods include Direct Simulation (DS) with upwind scheme for laminar flow at Re = 200, 400, 103, and k−e model for turbulence flow at Re = 4 × 103. The simulations were conducted at various blockage ratios of H L = 0.04, 0.067, 0.085, 0.112, 0.166, 0.244, 0.303 and 0.4 . For stationary cases, simulations were carried out at Reynolds numbers of Re = 200−103. For oscillation cases, simulations were done at Reynolds number of Re = (1, 4) × 103 for a square cylinder oscillating at forced oscillatory frequencies of Stc = 0.1, 0.25 and 0.3. Using the SIMPLE algorithm, simulation results show that drag and lift forces and Strouhal numbers all increase with the increase of blockage ratios (i.e. the decrease of the interval of the two parallel confining walls), and the aerodynamic characteristics agree reasonably well with those from experiments. For stationary cases, the lift and drag forces, and vortex-shedding Strouhal numbers all increase with the increase of blockage ratios. The flow streamlines and vorticity contours show conspicuous features of the wake under high blockage ratios. The first-sinking phenomenon due to blockage effect can be successfully captured at Reynolds numbers of only Re = 103 and can be confirmed to be caused by the change of non-reattachment of separated shear layers to reattachment flow by the blockage effects. For oscillation cases, the lock-in features are successfully captured. The behavior of phase difference, i.e. the stable/unstable features, against the forced oscillatory frequency cannot be almost influenced by the blockage effects.