Acoustic characteristics of gas flow in duct with sharp increase or decrease of stationary mass flow rate

An analysis of the relation between acoustic properties of a gas flow and parameters of sharp increase or decrease of a stationary mass flow rate has been performed for a straight channel with an inlet and outlet with supercritical pressure difference. Plane harmonical sound waves have been generated far upstream of the inlet by a special device with sinusoidal variation of the cross-section. Parameters measured are instantaneous and fluctuating pressure values directly ahead and behind the inlet. The equations for the one-dimensional harmonical isoentropic flow of a nonviscous gas are obtained in the form of a dynamic transfer function which correlates fluctuating mass flow rate and total entalpy at the inlet of the channel element to the same parameters at the outlet. The predicted results have been compared with the data obtained experimentally. The coincidence is very satisfactory.