Experimental investigation of two-phase flow evolution in a high-speed submerged water jet with air ventilation

Abstract

In order to improve the submerged cutting performance of water abrasive suspension jet an experimental investigation on the two-phase flow structure of submerged water jet with semi-coaxial air ventilation is conducted by the method of high-speed camera observation under the condition of flow dynamic similarity, and its unsteady behavior under different conditions is evaluated by analyzing of sequence images. Experiment results show that the flow pattern of air-ventilated jet depends upon the ventilation flow rate. It may be classified into bubbly flow surrounded jet, continuous air-layer covered jet and cavity-bubble flow surrounded jet. In the case of non-ventilation, high-speed water jet into water is accompanied by intensive cavitation and the flow field appears to be a narrow jet surrounded by cavitation bubble clouds. By ventilating to the cavitating jet, air-bubbles become bigger gradually and a cavity area is formed at the exit of nozzle head. When the ventilation flow ratio reaches to the level of 5 a large cavity covering the jet is formed and a continuous air-layer covered jet is then generated. Image analysis demonstrates that the continuous air-layer covering the liquid jet pulsates and sheds downstream periodically. The Strouhal number defined by the dominant frequency of jet pulsation decreases quickly with the increase of ventilation flow rate in the range of Cq ≤ 5. At a suitable ventilation flow ratio (Cq ≈ 6 ~ 8) a relative long stable continuous air-layer covering the jet is generated at high time ratio, which will dramatically enhance the processing ability of submerged water jets. Cutting tests demonstrates that the cutting ability of air ventilated jet depends on the ventilation flow ratio. The relation of processing ability with the flow structure of air ventilated jet is clarified.