An extremely interesting problem in aero-hydrodynamics is the sound radiation of a single\nvortical structure. Currently, this type of problem is mainly considered for an incompressible medium.\nIn this paper a method was developed to take into account the viscosity and thermal conductivity of\ngas. The acoustic radiation frequency of a cylindrical vortex on a flat wall in viscous heat-conducting\ngas (air) has been investigated. The problem is solved on the basis of the Navierââ?¬â??Stokes equations\nusing the small initial vorticity approach. The power expansion of unknown functions in a series\nwith a small parameter (vorticity) is used. It is shown that there are high-frequency oscillations\nmodulated by a low-frequency signal. The value of the high frequency remains constant for a long\nperiod of time. Thus the high frequency can be considered a natural frequency of the vortex radiation.\nThe value of the natural frequency depends only on the initial radius of the cylindrical vortex, and\ndoes not depend on the intensity of the initial vorticity. As expected from physical considerations, the\nnatural frequency decreases exponentially as the initial radius of the cylinder increases. Furthermore,\nthe natural frequency differs from that of the oscillations inside the initial cylinder and in the outer\ndomain. The results of the paper may be of interest for aeroacoustics and tornado modeling.
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