Flow and sound field characteristics of a Hartmann whistle with flow-sound-separation feature

Abstract

Acoustic agglomeration technology can arouse relative motion and rapid agglomeration for aerosol particles. Traditional electroacoustic transducers are commonly used in laboratories to produce high-intensity sound, but they are fragile and have low conversion efficiency. Hartmann whistle is a kind of air-jet generator with the characteristics of simple structure, absence of moving parts and high sound power. However, as a Hartmann whistle works, the spent airflow would be produced at the exit of the horn along with the sound field, which will push the aerosol particles away from the sound source and reduce the agglomeration efficiency. To solve the problem, this paper proposes a new Hartmann whistle with flow-sound-separation feature for the first time, and the influence of opening ratio (X/L) and inlet air pressure is studied by numerical simulation. Results show that when the opening ratio is 0.5, the air flow rate at the exit of the horn is reduced to 0 kg/h, which means that all of the spent air exhausts from the side opening. Meanwhile, the sound efficiency is decreased by 19 %. The air flow rate of the side opening increases with the increasing opening ratio or inlet air pressure. As the opening ratio exceeds 0.5, there will be backflow at the horn. The total sound power of the whistle maintains constant with the variation of opening ratio, and reaches the maximum value of 39 W at 0.275 MPa.