Acoustic Losses of a Resonator with Steady Gas Flow

Abstract

Measurements have been made of the acoustic losses of a resonator with a small vent and of their dependence both on the speed of steady flow through the system and on the position of the vent. The resonator is physically modeled on the “T burner” used to test solid propellants for combustion instability, but measurements are made at room temperature and pressure. It is a closed circular cylinder, resonant in the fundamental plane-wave mode, with a vent through the wall near the center. Steady gas flow is introduced at one end through a slightly porous piston whose vibration also generates sound. Losses are determined from the rate of decay of pressure. Significant flow-dependent loss attributable to the vent is found for flow speeds in the vent exceeding about 0.02 times the sound speed. The loss depends on vent position. Good quantitative prediction of this loss at flow velocities above a critical value is achieved by a theory based on the characteristics of quasisteady fluid efflux from an orifice (total pressure quadratic in total flow).