Acoustic liner acoustic impedance measurement method under condition of acoustic wave grazing incidence

Abstract

The invention discloses an acoustic liner acoustic impedance measurement method under a condition of acoustic wave grazing incidence. The method includes the steps of installing an acoustic liner on a side wall of a sound transmitting tube having a rectangular cross section; obtaining wall sound pressure of the position where M measurement points are selected on an opposite side to the side wall where the acoustic liner is located; based on modal characteristics of sound propagation in a tube, enabling the wall sound pressure of the sound tube to be written in an exponential function superimposed form, so that the number of axial wave of sound propagation in the sound tube can be identified through a Prony method; then extracting acoustic impedance in two cases, an when the gas in the sound tube is uniform flow, obtaining the acoustic impedance simply by using a simple dispersion relation and an eigenvalue equation; and when the gas in the sound tube is shear flow, obtaining the acoustic impedance by using an impedance boundary condition after a Pridmore-Brown equation is numerically solved. The advantages of the invention lie in that compared with conventional extraction methods, the acoustic liner acoustic impedance measurement method greatly simplifies the extraction process, reduces the number of measurement points of the wall sound pressure, and is free from the influence of reflection from an outlet; and the invention provides a novel test method for the industry community.

Description

technical field [0001] The invention belongs to the field of aerospace technology, in particular to a method for measuring the acoustic impedance of an acoustic lining under the condition of grazing incidence of sound waves. Background technique [0002] As a sound-absorbing structure, acoustic lining is widely used in architectural design and industrial equipment, and its function is to absorb and reduce noise. For the specific application of aero-engines, the various mechanical properties of the acoustic lining are very strict. It is required that the acoustic lining has the minimum thickness and weight and can withstand considerable pressure and temperature. Of course, the most important thing is to Has excellent noise reduction performance. Aeroengines mainly use local response acoustic linings. Therefore, whether the impedance value of local response acoustic linings can be accurately measured is of great significance to engine noise reduction. [0003] Impedance is d...

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Problems solved by technology

[0018] In order to solve the above problems, the present invention proposes an extraction test method that can meet the measurement requirements and is efficient in a short time, so as to solve the problem of extraction of the acoustic impedance of the acoustic lining under the condition of grazing incidence of the sound wave, and achieve that it does not depend on the boundary conditions of the entrance and exit, and can be applied as much as possible Small number of microphone measurement points and process calculation time

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