Active Suppression of Supersonic Jet Noise Using Pulsating Micro-Jets

Paper in proceeding, 2012

Noise suppression devices on military jet engines are motivated by the need to reduce community noise as well as the acoustic load on airfield personnel during peacetime operation. They may also reduce problems with sonic fatigue on the aircraft. Micro-jets have previously been shown as a promising tool for active noise suppression. In the work presented here, compressible LES simulations have been done for slightly overexpanded conical C-D nozzle with a Mach number of 1.58 at NPR = 4.0 and a free stream flow Mach number of 0.1. Two microjet configurations have been simulated. One with steady-state injection and an other with pulsating trailing-edge injection having a maximum mass flow-rate of mi/mj = 1.6%. The acoustic field is expanded to the far field using the Kirchhoff integral method. The effect of injection frequency and pulsation characteristics on the flow-field and the radiated sound is investigated. Comparison is made between the LES and simulations and experiments for the steady-state and no injection cases and shows excellent agreement for the screech tone frequency and the predictided OASPL is within 2 dB deviation from the measurements. The pulsating injection cases investigated show that the frequency spectrum and the noise levels are sensitive to the injection frequency as well as pulsation characteristics. It is shown that steady-state injection and pulsating injection of equal max mass flow result in comparable reduction in terms of OASPL. The latter, however, comes with the penalty of increased noise for the upstream observers.