Passive Jet Approach to Control the Flow over a Circular Cylinder

Abstract

A numerical investigation was conducted on a passive jet flow control method for alleviating unsteady wake oscillation behind a circular cylinder. The study focused on the effects of two crucial parameters—the number of jet holes in a pipe and the radial thickness of a pipe—on the aerodynamic forces acting on a circular cylinder and alternating vortex shedding in the wake. Pressure coefficient distributions, aerodynamic coefficients, vorticity distributions, probability density functions of wake velocities, and production of turbulent kinetic energy were analyzed in detail. Both the fluctuating lift force and the mean drag force acting on the model decreased with an increase in the jet momentum coefficient. The optimal parameters were a 13-hole pipe and a 5% ratio of pipe radial thickness to the cylinder diameter. Under the optimal parameters, fluctuating lift was reduced by 99.57% with a mean drag reduction of 32.41% compared with a bare cylinder. The fluctuating wake of the circular cylinder was almost eliminated. The alternating vortex shedding was converted into two parallel shear layers, and the asymmetric vortex shedding mode was shifted into a symmetric wake mode. The probability density function of the fluctuating transverse velocity in the wake shrank without wide tails, because the production of turbulent kinetic energy in the wake was reduced by over one order of magnitude, which is the intrinsic nature of this passive method to effectively suppress the aerodynamic forces on a circular cylinder and wake oscillation.