A Comprehensive Investigation of Pulsed Fluidic Injection for Active Control of Supersonic Jet Noise

Paper in proceeding, 2013

Fluidic injection for noise control of high Reynolds number jets has shown promise and recent tests have demonstrated improved noise reduction while decreasing the injection mass flow required. This investigation was an experimental and numerical study on the capability of pulsed fluidic injection to reduce noise on a Md = 1.56 supersonic jet. The effect of pulse frequency, duty cycle, injector phasing, and injection angle on the noise components were studied. The pulsed injectors were characterized with hot-wire measurements. Far-fleld acoustics was used to survey the noise reduction of pulsed injection (up to 400 Hz) in comparison to the baseline and steady injection cases. Injection angles θinj = 30° to 90° with respect to the primary jet axis were investigated. High-speed shadowgraph was used to quantify the time scales involved in response of the shock train and screech instabilities with pulsed fluidic injection. LES and CAA were compared with measurements to evaluate the capability of numerical simulation of the pulsed injection configurations. It was shown that reduction of turbulent mixing noise generally scales with the actual duty cycle of applied injection. For 30 Hz injection at 20% mass flow up to up to 80% of the steady flow {increment}OASPL is achieved, demonstrating that low frequency injection is capable of enhanced noise reduction at certain conditions. The shocks in the jet potential core respond in 1 ms when injection is removed, while the jet column instability requires up to 7 ms to redevelop after injection is removed. The results demonstrate the feasibility of using active control with pulsed fluidic actuators to provide at least steady flow noise reduction with significantly reduced injection mass flow.