Measurement of Acoustic Reflection from Obstructions in a Pipe with Flow,

摘要

A technique has been developed to measure the reflection coefficients for simple plane waves incident upon a pipe obstruction (orifice,valve,etc.) in the presence of flow. The method uses correlation techniques to decompose an acoustic standing wave into incident and reflected travelling waves for the range 100-2100Hz. Three orifices with diameters of 3/4, 1-1/4,and 2inches were tested in the 3.82inch diameter pipe of a new aeroacoustic test facility. The experimental reflection coefficients from the 3/4and 1-1/4inch orifices compare favorably to available analytic results for both the flow and no flow cases. The reflection coefficients,without flow,increase with increasing frequency, i.e. they have the characteristic of acoustical low pass filters. When flow is present,the reflection coefficients are nearly constant across the test frequency range,for a particular flow M sub i,the indicated Mach number of the jet that issues from the orifice.