The Research Of Acoustic Characteristics Of Aircraft Environmental Control System Silencer

The commercial aircraft cabin noise level is one of the important indicators to evaluate ride comfort.The main noise sources of cabin noise include engine noise,noise of turbulent boundary layer,and noise from the internal environment control components,such as pipe and air conditioning.The ECS(environmental control system)noise can be controlled by installing silencers in pipelines.The silencer design involves calculation and analysis of multi-physical fields,such as fluid mechanics,structural dynamics and acoustics.In addition,the design of commercial aircraft silencers has strict constraint in weight and space.Hence,the performance prediction of ECS silencers and structure optimization are complex but important.At present,the silencer design mainly depends on empirical equation to predict performance.But,it can't satisfy the requirements of the commercial aircraft silencer design.In order to control the ECS noise in the cabin of the commercial aircraft,a prediction model of the acoustic performance of ECS silencers was developed with the finite element method(FEM).By using this model,the sound transmission loss and air pressure loss of the typical silencers,e.g.the straight pipe dissipative silencer,inserted duct silencer,impedance compound silencer and perforated tube impedance compound silencer,were analyzed.The simulated results coincided with experimental results on the sound transmission loss.Under the flow velocity of low Mach(20 m/s),the air pressure loss of the silencer is very small and therefore can be neglected.The selection of the sound absorption materials which was used by the silencer involved the measurements of the acoustic parameters of the aviation materials.Through the research on the relationship between the sound transmission loss of the silencer and the measured acoustic parameters,we ensured that the flow resistivity was the most important acoustic parameter.The lower the flow resistivity of the material is,the higher the sound transmission loss of the silencer can be achieved.Based on the measurements,a database of the acoustic characteristic of aeronautical materials was created to provide the parameter query for the silencer design of aircraft ECS.In order to validate the prediction model,the experimental work on the sound transmission loss of the perforated tube impedance compound silencer with two different absorption materials(glass fiber cotton and sponge sound absorption)were carried out.The results shown that the calculated results coincided well with experimental values in the whole frequency range,which means the prediction model is credible.By using the prediction model,the suitable type of silencers and acoustic materials were selected for application of the commercial aircraft.A design flow of the aircraft ECS silencer was created to satisfy the requirements of the commercial aircraft silencer design.The study of the thesis provides the theoretical and practical guides for design of silencers in the civil aircraft.