EFFECT OF GRAZING–BIAS FLOW INTERACTION ON ACOUSTIC IMPEDANCE OF PERFORATED PLATES

✍ Scribed by X. SUN; X. JING; H. ZHANG; Y. SHI

• Publisher: Elsevier Science
• Year: 2002
• Tongue: English
• Weight: 305 KB
• Volume: 254
• Category: Article
• ISSN: 0022-460X
• DOI: 10.1006/jsvi.2001.4110

✦ Synopsis

In this paper, the e!ect of grazing}bias #ow interaction on the acoustic behavior of a perforated plate is investigated. In the experiment, bias #ow into or out of ori"ces (in#ow or out#ow) is used to change the acoustic impedance of the test perforated plates subjected to grazing #ow, and the acoustic impedance is measured as a function of both grazing and bias #ow speeds. A comparison is made between the present measured ori"ce acoustic resistance and the previous results for steady state ori"ce resistance. Qualitatively, both results show similar characteristics. It is shown that there is some di!erence between grazing-in#ow and grazing-out#ow interactions. In the out#ow case, grazing #ow results in the drop of the acoustic resistance below the non-grazing #ow value at high bias #ow speed, whereas it generally has the e!ect of increasing the acoustic resistance in the in#ow case. Furthermore, a simple grazing}bias #ow interaction model is set up in an attempt to explain the observed phenomena. This model shows that the acoustic resistance of an ori"ce in a thin plate is proportional to bias #ow Mach number, and is inverse to the square of the e!ective discharge coe$cient which depends only on the ratio of bias #ow speed to grazing #ow speed. Finally, based on the theoretical analysis and the experimental data, an empirical equation is presented for the e!ective discharge coe$cient.