Steady active control of noise radiation from highly heated supersonic jets.

Abstract

The goal of the present investigation is to study the effect of using fluid inserts for noise control at high exhaust temperatures by performing a sequence of large eddy simulations on a typical military-style nozzle, both with and without fluid inserts, at jet inlet total temperature ratios of 2.5, 5, and 7. An exact physics-based splitting of the jet flow-field into its hydrodynamic, acoustic, and thermal components reveals clear evidence of a reduction in the radiation efficiency of Mach waves from the controlled jet. This effect is far more pronounced at afterburner conditions, where the location of the maximum noise reduction is observed to shift upstream with increase in jet temperature, thus matching the maximum location of the jet OASPL directivity. Moreover, the maximum noise reduction achieved at afterburner conditions exceeds that obtained at lower exhaust temperatures. This is encouraging and shows that the effectiveness of the fluid inserts improves with an increase in jet exhaust temperature. Furthermore, by accounting for the effect of bleeding off bypass air for the fluid inserts in the LES simulation, this noise reduction is predicted to be achieved at a conservative thrust loss estimate of under 2% at both laboratory and afterburner operating conditions.