Separation Control Using Zero-Net-Mass Perturbations: Effect of the Duty Cycle

This study aims to investigate the influence of the duty cycle, DC, of zero-net-mass perturbations applied to active separation control. To that extent, a unique flow control apparatus producing alternating pulsed blowing and suction was implemented on an academic separated flow configuration. Three series of constant mass-flow coefficient perturbations were studied, for each of which values of the duty cycle ranged from 10 to 80 %. The results indicate that a better control efficiency is achieved for lower values of the duty cycle in terms of dimensions of the separation bubble and pressure distribution, at the cost of a higher fluctuating flow. The transient mechanisms involved in the periodic actuation were studied, highlighting the different timescales governing the controlled flow. The blowing phase was shown to be the main contributor to flow reattachment, whereas suction makes the flow more robust to separation.