Control of wakes and vortex-induced vibrations of a single circular cylinder using synthetic jets

This paper presents a study on active control of the wakes and one-dimensional vortex induced vibrations (VIVs) of a single circular cylinder using a pair of synthetic jets (SJs) at a low Reynolds number Re=100. To facilitate this study, a lattice Boltzmann method based numerical framework is established, in which the multi-block scheme and the overlap mesh approach with improved information exchange mechanisms are used to balance the computational accuracy and efficiency, and the interpolated bounce-back scheme and a corrected momentum exchange scheme are adopted for accurate force evaluation. Two configurations are considered. In the first configuration, the cylinder is fixed, on which a pair of SJs is implemented and operates in phase. Effects of the SJ pair on the cylinder wake are investigated in a systematical way, with the focus placed on the SJ's momentum coefficient, frequency and position. Simulation results indicate that the Karman vortex street formed behind the cylinder can be effectively suppressed when the SJ pair operates with sufficiently high momentum coefficient, at a frequency close to the cylinder's natural vortex shedding frequency, and is placed in the quarter arc edge of the cylinder's leeward side. In the second configuration, the same cylinder is allowed to oscillate in the cross flow direction under the excitation of asymmetrically shedding vortices as well as the constraint of a spring. It is well demonstrated that this one-dimensional VIV of the cylinder can be successfully suppressed by the use of SJ control. Due to stronger vortex shedding induced by increased relative motion between the cylinder and its surrounding flow, however, not all the cases that perform complete wake suppression on the fixed cylinder are able to completely suppress the VIVs of the oscillating cylinder. Through the present study, details about SJ-controlled flow around the cylinder and in the wake are also revealed. (C) 2015 Elsevier Ltd. All rights reserved.