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ACTA AERONAUTICAET ASTRONAUTICA SINICA ›› 2020, Vol. 41 ›› Issue (11): 223860-223860.doi: 10.7527/S1000-6893.2020.23860

• Solid Mechanics and Vehicle Conceptual Design • Previous Articles     Next Articles

Single and double degree-of-freedom acoustic liners under grazing flow: Experiment

YANG Jiafeng1,2, XUE Dongwen1,2, LI Zhuohan1,2, HUANG Taiyu1,2, XU Jian1,2   

  1. 1. Aircraft Strength Research Institute, Xi'an 710065, China;
    2. Key Laboratory of Aeronautical Acoustics and Vibration, Xi'an 710065, China
  • Received:2020-02-03 Revised:2020-02-29 Online:2020-11-15 Published:2020-03-20

Abstract: Two acoustic liners, one of Single Degree-Of-Freedom (SDOF) and the other of Double Degree-Of-Freedom (DDOF), are separately tested on a flow duct in the laboratory to compare their acoustic performance with grazing flow up to 0.26Ma. The normalized impedance of the liners is educed by Straight Forward Method (SFM), and the acoustic energy Transmission Loss (TL) and absorption coefficient of the liner-installed section are determined with the two-microphone method. The differences in acoustic performance between the two tested liners can be observed through TL as well as the impedance. Tested results show that the DDOF liner effectively broadens the sound absorption band compared with the SDOF liner on the flow duct. However, its maximum TL is less than that of SDOF. The grazing flow significantly changes the resonance frequency of the acoustic liner and weakens the sound absorption performance. Furthermore, the transmission loss and absorption coefficient based on sound energy also provide a new method for the assessment of the non-uniform structure acoustic liner which cannot be described with equivalent impedance.

Key words: double degree-of-freedom liners, sound propagation in flow duct, acoustic impedance, straightforward method, transmission loss, absorption coefficient

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