Features of sound generation by the jet-driven Helmholtz oscillator

Abstract

Experimental studies the model of a jet-driven Helmholtz oscillator has been carried out. The oscillator is a cylindrical chamber, closed on the sides by two covers with inlet and outlet holes. The oscillator was excited by a stream of airflow. The influence of the geometric dimensions of the chamber and the openings in the covers on the amplitude of pressure fluctuations was studied and the optimal channel configuration was determined. Particular attention is paid to the study of the influence on the amplitude of pressure fluctuations of the shape and size of the nozzle - the hole in the front cover. There were measured the following processes: the pressure drop across the nozzle, to calculate the speed of the jet at the chamber entrance, and the parameters of pressure fluctuations in the chamber, to plot the amplitude-frequency spectra. There were made certain observations of a jet tone appearance and acoustic modes excitation at the natural frequency of the chamber-resonator with a smooth increase in the jet velocity. The relationship between the jet tone and the resonant in the chamber is noted. Recommendations for designing a Helmholtz jet oscillator are presented.