Wake control using synthetic jets

Abstract

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.The interactions of wake of an elongated bluff body and the periodic flow emanating from a pair of synthetic jets placed symmetrically at the trailing edge, spanning the width of the plate, were experimentally studied for the purpose of quantifying the flow physics that led to wake drag reduction. The experiments were carried out in a low turbulence wind tunnel at Reynolds number, Reh based on the flat plate thickness h, of about 7200. The synthetic jet actuators, providing a global momentum addition of Cμ=24%, were positioned symmetrically at the model base at a distance of ± 0.27 h from the base centerline to introduce perturbations at early stages of the shear layers’ development. The synthetic jet actuation frequency was selected to be about 75% the vortex shedding frequency of the natural wake. Two-component velocity measurements were acquired using Particle Image Velocimetry (PIV) and reported for natural wake and controlled wake using symmetric synchronous actuation and out-of-phase actuation. In this work, mean velocity profiles, Reynolds stresses and coherent structures and their dynamics in the wake of a bluff body were evaluated as the initial conditions (injection configurations) were changed. Furthermore, phaseaveraged velocity fields through the vorticity contours were determined to provide insights into the actuation mechanisms namely, the role of the synthetic jet vortex structures on the flow dynamics.