The Study On Algorithm Of Acoustic Absorption By The Atmosphere In Aircraft Noise Airworthiness

In the aircraft noise airworthiness certification, the calculation of sound absorption is indispensable. The atmospheric acoustic absorption calculation method which is used in CCAR 36 issued by China is based on the calculation method which is given in the SAE ARP866 A. The new atmospheric acoustic absorption calculation method has published in the SAE ARP5534.At first, there is an introduce about the development of the atmospheric acoustic absorption calculation method and it gives the calculate process of SAE ARP866 A and SAE ARP5534. Besides, the calculate result is influenced by the four factors: atmospheric pressure, temperature, relative humidity and the frequency of the sound. The aircraft noise measurement data which has been given by ICAO is used to calculate the atmospheric acoustic absorption coefficient and EPNL. The calculation results are analyzed behind the paper.As can be seen from the analysis results, there is a great difference between the two methods. The ARP5534 algorithm uses the pure-tone absorption and ARP866 A algorithm is with 1/3 octave absorption. The ARP5534 method has considered the effect of atmospheric pressure on atmospheric acoustic absorption, and the ARP866 A algorithm did not consider this factor. From the calculated results and curve, we can also see the atmospheric acoustic absorption have a great fluctuation within the scope of the high frequency. In addition, the algorithm which uses the ARP5534 to calculate the EPNL is higher than ARP866 A.In a word, ARP5534 atmospheric acoustic absorption calculation method gives a better way to represent the physical mechanisms of sound absorption by the atmosphere. The atmospheric acoustic absorption coefficient can be calculated under the extreme environment conditions. It can improve the accuracy of the atmospheric acoustic absorption coefficient. A great help will be given to improve the aircraft noise airworthiness certification.