SOUND GENERATION BY AIRBORNE AIR-CONDITIONING SYSTEMS - THEORY AND ANALYSIS

A method is presented for (a) deriving the contribution of the air con ditioning system to the overall acoustic field in aircraft cabins, (b) defining the noisiest sources of the system; and (c) designing the ai r conditioning system muffler characteristics. The method is based on analysis of the sound flow energy in air conditioning system channels including both the generation and attenuation effects of the acoustic oscillations within the system. Basic expressions of calculation metho d are worked out upon. acoustic characteristics of the system units li ke throttle valve, controlling units, ejectors, cooling turbines, cock pit air distribution systems; characteristics of noise attenuation in line sections of the system, in pipe bends of various forms, in the sy stem units, in the elements of the distribution system, etc. The relia bility and accuracy of the method has been evaluated by comparing the results of simulation with noise levels measured in aircraft while in operation. Far frequency bands above 315 Hz and the main operation mod es, this model gives good results in cockpits and cabins. (C) 1998 Els evier Science Ltd. All rights reserved.