Correction method of estimated insertion-loss based on the four-pole parameters. Effect of mean flow and temperature gradient.

Abstract

The four-terminal transmission matrix method as the representative method of theoretical research on mufflers has been widely used. However, the predictions using the equations in the four-terminal transmission matrix method do not reflect a practical phenomenon accurately, because the computation is carried out under assumptions such as the system would be linear, isentropic, zero mean flow, zero temperature gradient, and so on. In this paper, we examine some aspects of the errors ensuing from some assumptions in the four-terminal transmission matrix method by using the Characteristic Curve Method. Also the method of correction for the D parameter is presented. The method of correction to the four-terminal transmission matrix method was proposed by rewriting the real and imaginary parts as they depend solely on the flow velocity. Then the result was compensated for by adding the component of the temperature gradient.