Upstream open loop control of the recirculation area downstream of a backward-facing step

TL;DR

This study investigates upstream pulsed jet control of flow separation behind a backward-facing step, demonstrating effective recirculation area reduction at low jet amplitudes and duty cycles, with implications for flow management.

Contribution

It introduces upstream pulsed jet actuation as an effective method to control recirculation zones, comparable to edge actuation, with minimal energy input.

Findings

Upstream actuation can match step-edge control efficiency.

Optimal control achieved with low jet amplitude and 10% duty cycle.

Recirculation area nearly eliminated with minimal actuation.

Abstract

The flow downstream a backward-facing step is controlled using a pulsed jet placed upstream of the step edge. Experimental velocity fields are computed and used to the recirculation area quantify. The effects of jet amplitude, frequency and duty cycle on this recirculation area are investigated for two Reynolds numbers (Re=2070 and Re=2900). The results of this experimental study demonstrate that upstream actuation can be as efficient as actuation at the step edge when exciting the shear layer at its natural frequency. Moreover it is shown that it is possible to minimize both jet amplitude and duty cycle and still achieve optimal efficiency. With minimal amplitude and a duty-cycle as low as 10\% the recirculation area is nearly canceled.