Active Suppression of Supersonic Jet Noise Using Pulsating Micro-Jets
Paper i 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.