Studying the thermal effect in a swirled acoustic flow

Abstract

Abstract. The mechanism of generation of acoustic oscillations associated with the formation of stable vortex structures in a moving medium is considered on the example of impact swirl flow. A selfregulation effect was detected for condition, when the limiting flow rate of a swirl flow has been reached. This effect is expressed in resonance amplification of the amplitude of the natural frequencies of the hydromechanical system due to the absorption of the component of the spectrum of acoustic oscillations generated by the vortex structure of the flow. A redistribution mechanism for the energy of an open system at resonance, associated with the influx of air from the external medium is considered. Temperature distributions on the lower surface of the obstacle were obtained using the thermal imager, and the energy losses associated with the flow cooling due to expansion were estimated.An experimental investigation of the thermal effect in a swirled acoustic flow was carried out within the framework of studying the effect of self-regulation of acoustic oscillations in a hydromechanical system in the pre-resonance and resonance regimes [1]. A detailed description of the experimental setup is given in [2]. The vortex chamber was a rigid metal vessel with plexiglass upper surface with central hole through which a swirled air stream was flowing out. To organize the impact character of the flow above the outlet opening, made in the form of a confuser, an unfixed barrier in the form of a flat disc was placed. During the measurements, the amplitude-frequency characteristics of acoustic oscillations were recorded; they carried information about the change in the local pressure field, visualization patterns of the vortex structure and the inhomogeneities of the flow, as well as the temperature field on the lower surface of the barrier [3].With the help of thermal imaging measurements, it was found that the formation of a stable large-scale spiral-vortex structure in the form of a torus with a double rotation in the region of the expiration of an impact swirled jet occurs with the conversion of thermal energy into mechanical energy (Fig.1).