A new free-surface flow problem is considered. The problem is complicated by the unsteady and three-dimensional nature of the flow and the ponderability of the fluid. The features of unsteady cavitation interaction of coaxial water and annular gas jets with countermoving water flow in cylindrical pipe are investigated numerically and experimentally. The onset pattern and main features of regular self-oscillating interaction regimes are studied. The dependence of mean oscillation frequency on countermoving jets velocity ratio and gas jet discharge is determined. The influence of the Froude number upon the frequency of self-oscillations is analyzed. The relation between the increase in supplied gas discharge and both the maximum longitudinal displacement of cavity tip into counter-current flow and the amplitude of displacement is determined. The pressure distribution along the cavity is obtained at different stages of flow formation. Similar relationships are found for some values of relative cross-section area reduction due to the presence of cavity. These relationships give an estimate of the pipe walls influence on the characteristics of unsteady developed cavity flows.
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