Effects of forward velocity on noise for a J85 turbojet engine with multi-tube suppressor from wind tunnel and flight tests

Abstract

In order to obtain an understanding of the effects of forward velocity on exhaust noise suppression, flight and wind-tunnel noise tests were conducted using a J85 turbojet engine. Nozzle configurations of primary interest were a 104-tube suppressor with and without an acoustically treated shroud. Engine installation was as nearly idential as possible for both flight and wind tunnel tests. Some differences necessarily existed, however; e.g., for the flight tests the engine was in motion with respect to the microphones, and for the wind-tunnel tests it was not. Exact simultaneous matching of engine speed, exhaust velocity, and exhaust temperature was not possible, and the wind-tunnel maximum Mach number was ∼0.27, while the flight Mach number was ∼0.37. The nominal jet velocity range was 450–640 m/sec. For both experiments, background noise limited the jet velocity range for which significant data could be obtained. The observed forward velocity effects for the suppressor indicate that jet noise has been suppressed to a level where the in-flight directivity is similar to that expected for internally generated noise.