Tapered Cavity Acoustic Performance Of The Hartmann Whistle

Sound generators of various forms are needed in acoustic research. Aeroacoustics is faced with research environments about high sound pressure level and wide frequency band. The air current sound generator is exactly the most suitable sound source providing this kind of environment. The air current sound generators at present include the Hartmann whistle, vortex whistle, jet-edge whistle (resonant wedge whistle), single-hole jet rotary valve, multi-hole jet rotary valve, and so on. Although the pneumatic sound source has been put into many applications currently, its sound generating mechanism is always a big problem until now. Especially, the Hartmann whistle has been widely applied in the fields such as the metallurgy (blast atomizing), ash removal, dust removal, and petroleum industry; but the key problem, also the problem demanding prompt solution, is the mechanism issue of the resonant cavity of the Hartmann whistle switching among several different resonance modes, and the stability issue of the resonance tube brought subsequently. because of the difficulty of the problem itself, it has not been solved up to now.In the improvement of the Hartmann whistle for different purposes, the conical cavity type Hartmann whistle is representative, which has been widely used as the engine igniter of a rocket, therefore, researchers are more interested in the research of the thermal effect of the H-S cavity. It is proposed that the conical cavity type Hartmann whistle and cylindrical cavity type Hartmann whistle have the same flow field, however, no detailed research has been made on their acoustic characteristics, especially those of the small-size conical cavity type Hartmann whistle, so there is a little of literature on the acoustic characteristics of the small-size conical cavity type Hartmann whistle.In this paper, the theories and experimental researches of predecessors on this field are summarized and introduced firstly; the acoustic characteristics of the conical cavity type Hartmann whistle is researched by experimental methods; finally, the acoustic characteristics of the small-size Hartmann whistle and conical cavity type Hartmann whistle are compared, and their sound generating mechanisms are analyzed and studied by combining research results.In summary, this paper is focused on the following aspects:1. The research progress and application of the Hartmann whistle are summarized and introduced.2. The sound generating mechanism of the Hartmann whistle is studied, and the conical cavity type Hartmann whistle is designed.3. The acoustic characteristics of the small-size cylindrical cavity type Hartmann whistle and conical cavity type Hartmann whistle are studied by comparative experiments. They have similar acoustics characteristics.4. The effect of extra pressure in front of nozzle to the acoustic characteristics of the conical cavity type Hartmann whistle are investigated. frequency and sound pressure level increase with the extra pressure in front of nozzle. And the experiment that this paper discusses was found to be in agreement with the linear acoustic theory .5. The effect of conicity of the resonant cavity to the acoustic characteristics of the conical cavity type Hartmann whistle are investigated. the smaller conicity is, The higher Frequency is,but it is opposite with the relation between the sound pressure level and the conicity of the resonant cavity.6. The effect of the stand-off distance between jet exit and cavity inlet distance to the acoustic characteristics of the conical cavity type Hartmann whistle are studied.The Hartmann whistle is resonant when the stand-off distance between jet exit and cavity inlet distance is beween 1mm and 2mm.7. The effect of flow rate that is measured in front of nozzle to the acoustic characteristics of the conical cavity type Hartmann whistle are studied. The effect of the extra pressure and the flow rate in front of nozzle to the acoustic characteristics of the conical cavity type Hartmann whistle are similar.