Mathematical simulation of hydrodynamic generators of oscillations

Abstract

Unsteady turbulent swirled water flow in a channel in the presence of cavitation is calculated. It is shown that in the near-axial channel zone a fluctuating vapor region, or cavity, arises and variations in the cavity shape and dimensions lead to the onset of undamped pressure fluctuations. The amplitude-frequency characteristics of the oscillations are obtained in different channel cross-sections. The amplitude maximum position in the channel expansion zone is in agreement with the available experimental data. The dynamics of toroidal vortices formed in the hydrodynamic generator channel and in the expansion zone at its exit are established.Hydrodynamic generators of oscillations [1-3] produce waves when a fluid flows through channels of certain shape and dimensions. These generators have no any movable elements, which provides their reliability and service life. However, the mechanism of the pressure fluctuation onset has not been conclusively determined. It is noticed that these oscillations can be generated due to separation of toroidal vortices occurring in the channel [3] or as a consequence of the precession of a curved vortex core around the axis of symmetry of the chamber [4]. The purpose of this study is to numerically investigate the cavitation effect on the process of the pressure fluctuation onset in hydrodynamic vortex generators.

Generator geometry effect on wave dispersion of a gas in a liquid

“…Several mechanisms of the pressure fluctuation generation in hydrodynamic generators were established. These are the separation of toroidal vortices formed in the generator channel [3], separation and downstream convection of vapor regions in the presence of cavitation [6], the precessional rotation of a curved vortex core around the axis of symmetry of the chamber leading to the violation of the flow axial symmetry [7,8], and periodic variations of the shape and dimensions of the cavity formed in the lowpressure zone in the axial region of the channel [9,10]. One or another oscillation generation mechanism can be predominant depending on the hydrodynamic generator geometry and the operating regime.…”

“…For all gas flow rates considered the disperser with the channel diameter D = 5 mm showed better results than that with D = 7 mm. Apparently, this is due to the fact that in the channel having the smaller diameter fluctuations in the cavitation cavity lead to the more considerable variation in the effective duct cross-section [10] which enhances the pressure fluctuations and improves the dispersion fineness.…”