Control of a bluff body wake using travelling jets

Abstract

This work investigates the wake behind an axisymmetric bluff body at $R{e}_D\sim 2\cdot 10^5$ and applies control via four types of travelling jets which consist of different jet profiles undergoing travelling motion near the base edge. A comparison between these and the unforced wake is presented. Mean velocity, pressure fields, turbulence kinetic energy, and spectral proper orthogonal decomposition (SPOD) are employed to characterise the coherent structures within the flow. Our investigation confirms the presence of dominant modes and extends the previous findings to the velocity and pressure field on several planes parallel and perpendicular to the streamwise direction. These modes, as shown by SPOD, represent the wake’s bulk energy and therefore are the main target for travelling jets to pursue drag reduction. In the interest of achieving pressure recovery, several types of actuators have been proposed and investigated: the baseline travelling jet obtains the highest drag reduction with a pressure recovery of $+62\text{\%}$, which is followed by the oscillatory travelling jet with $+34\text{\%}$ and the pulsed travelling jet with $+32\text{\%}$; conversely, the sweeping travelling jet dramatically increases the drag with a $-460\text{\%}$ reduction in base pressure. Focusing on the baseline travelling jet, pressure recovery is achieved via a combination of dominant modes suppression, entrainment reduction, and wake’s elongation and narrowing.