Noise Characteristics and Simulation of Several Full Scale Turbojet Engines at Hush-House
Chiung Yao Chen, Cheng Ching Lee and Yee Hsiung Kuo

A hush house is arranged not only to maintain sufficient air flow through the wind tunnel but also to minimize the noise level with acoustical baffles inside the tunnels. An experimental investigation was conducted to determine the acoustic characteristics of several full scale turbojet engines of military fights inside the hush house. Acoustic measurements were taken outside the hush house at a distance of 75 m (far field) and inside or around (near field) the hush house from the fights. The military thrust data were obtained in and out of the hush house over a range of nozzle velocity up to 1247 (m/s). These military fights include TYPE-A and TYPE-B on active duty. For aircraft TYPE-A, maximum sound pressure levels in the far field were measured at the right front of inlet and the hush house exhaust wind tunnel. Noise levels at 75 m in far field decay by 8 dB as length of the wind tunnel was increased from 2.5m to 3.3m simulated using the ray acoustic method and confirmed by measured data diagnosed at Texas, USA.

Key words: acoustical baffles, micro perforated sheet, engine noise, sound propagation