Acoustic Properties of an In-duct Orifice Subjected to Bias Flow and High Level Acoustic Excitation

This paper experimentally investigates the acoustic properties of an orifice with bias flow under medium and high sound level excitation. The test included no bias flow and two bias speeds for three different frequencies. Experimental results are compared and discussed with theory. It is shown that bias flow makes the acoustic properties much more complex compared theory and with the no bias flow case, especially when velocity ratio between acoustic particle velocity and mean flow velocity is near unity.