4-POLE PARAMETERS OF A DUCT WITH LOW MACH NUMBER FLOW

The relationship between the four-pole parameters of a duct with and w ithout low Mach number flow is established. A transformation of the va riable is used to enable the sound propagation problem with low Mach n umber flow to be reformulated as the solution of an ordinary Helmholtz equation for the transformed variable. Thereby, the expression for th e four-pole parameters of a duct with flow is derived which can be det ermined by evaluation of the four-pole parameters for the case of the stationary medium. The results show there is a noticeable variation in the four-pole parameters, but there is not any variation in the trans mission loss with mean flow. (C) 1995 Acoustical Society of America.