Gasdynamic and Acoustic Characteristics of a Subsonic Jet-Edge Rod Generator of Acoustic Radiation
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Journal of Engineering Physics and Thermophysics, Vol. 93, No. 5, September, 2020
HYDROGASDYNAMICS IN TECHNOLOGICAL PROCESSES GASDYNAMIC AND ACOUSTIC CHARACTERISTICS OF A SUBSONIC JET-EDGE ROD GENERATOR OF ACOUSTIC RADIATION K. N. Volkov, V. N. Emel′yanov, A. V. Efremov, and A. I. Tsvetkov
UDC 532.529
The design of a subsonic jet-edge rod generator of the Hartmann-type oscillator and a scheme of measuring its acoustic parameters are presented. In this generator, unlike the Hartmann oscillator, not a cylindrical gas jet but an annular gas jet, moving along the thin cylindrical rod positioned at the axis of the generator nozzle, is used. A parametric investigation of the gasdynamic and acoustic processes arising in the tubular cavity of such a generator as a result of the interaction of a subsonic gas jet with this cavity has been performed with consideration for the nonstationary structure of the gas flow in the generator cavity. Recommendations on the choice of the design of a jet-edge rod generator of acoustic radiation with regard for its practical application are given. Keywords: jet-edge rod generator, Hartmann effect, acoustics, subsonic gas jet, generation of sound, amplitudefrequency characteristics. Introduction. A Hartmann oscillator comprises a conical convergent nozzle with a supersonic air jet emanating from it and a cylindrical cavity that is coaxial with the nozzle and faces the nozzle mouth. When a hollow tube is positioned in a supersonic gas jet, the interaction of the jet with the tube can proceed in a nonstationary (self-oscillation) regime with emission of an acoustic radiation into the environment (the Hartmann effect). In certain regimes of propagation of an air jet over a tube with a closed bottom, the surface temperature of the tube bottom can be higher by several times than the initial stagnation temperature of the gas flow (the Sprenger effect), and the temperature of the gas in the jet emanating from the tube is decreased. This effect arises in a resonance acoustic regime of a gas flow in such a tube, and the indicated temperature difference depends substantially on the distance between the nozzle from which a gas jet emanates and the open end of the tube. The unremitting interest of researchers in jet-edge generators is explained by the wide range of their technical applications. The work of such a generator is based on the Hartmann–Sprenger effect resulting in the emission of an acoustic radiation with a predominant discrete tone into the environment, the oscillations of the pressure in the tubular cavity of the generator, and the heat release in it. In this case, the frequency of vibrations of the gas in the generator cavity ranges from 100 Hz to 25 kHz, and their amplitude exceeds 150 dB [1]. In the jet-edge generators of sound with a frequency higher than 1 kHz and of ultrasound, an overexpanded supersonic gas jet or an underexpanded one serves as an energy source. In [2, 3], an acoustic generator with a subsonic gas jet has been devised. A design of an infrasound resonance tube o
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