Airworthiness Assessment Of Jet Noise For Civil Aircraft Engine

The globalization of the world is becoming more and more profound. In international economic and trade exchanges, large civil aircraft plays a more and more important role.China has carried out the independent research and development of large civil aviation aircraft on the agenda. Along with the increasingly stringent standards of international noise airworthiness certification, noise problem has become one of the major issues which need to face and pay attention to in the development of large civil aviation aircraft. Engine is the main noise source of aircraft noise, besides, jet noise plays an important role in engine noise.Firstly, the theory of three semi empirical models used to predict the jet noise is introduced: STNJET, ST2 JET and SAE. Then, according to the calculation principle of the three semi empirical methods and the idea of airworthiness assessment of jet noise, a kind of software is developed using the GUI module in MATLAB, named "Engine Jet Noise Prediction and Assessment". This software can realize the prediction, accuracy comparison,data analysis and the assessment of the jet noise for civil aviation engine. It is a fast and convenient engineering application software.Secondly, taking a certain engine as an example, the acoustic properties of the three components of jet noise: inner stream mixing noise, outer stream mixing noise and merged stream mixing noise, are studied by using this software. Because of the difference of the physical mechanism of noise, the 1/3 octave sound pressure level of the three components showed different distribution patterns. Then, the effect of the three models is compared and analyzed. Analysis results show that ST2 JET model is the best prediction method, it can be used as a tool for airworthiness assessment of jet noise.And then, based on ST2 JET model in this software, the accuracy of ST2 JET model is evaluated when using it to predict overall sound pressure level, A-weighted sound pressure level and effective perceived noise level of jet noise, and the acoustic characteristics of the three kinds of measurement parameters are also studied.Finally, based on the airworthiness certification program of the noise, the contribution of the jet noise to the engine noise is analyzed. The conclusion is that the jet noise has the largest contribution in the take-off stage, and the maximum acoustic radiation angle is 150 degrees.Based on this, the method of reducing the noise of engine by controlling jet noise is summarized.