Flow characteristics of high speed water jet and effective nozzle shape for machining

通过实验和数值分析，研究了两种高速水射流的有效喷嘴形状。一种是恒压50- 200 MPa、喷嘴直径0.155mm的淹没射流，另一种是速度500 m/s、喷嘴直径2 mm的脉冲射流。(1)CIP有限差分法是求解含间断界面气液两相流数值分析的有效方法。(2)在高速淹没水射流加工中，由于射流动量对材料的去除起着重要作用，因此在穿孔、钻孔或切割时，材料离喷嘴的距离应尽可能短。另一方面，间距取决于抛光或喷丸的输送压力，因为空化在表面处理中起主要作用。在这两种情况下，喷嘴帽的出口长度应取短，直径应取小。(3)本文用彩色Schlielen方法和高速摄像机对活塞冲击产生的脉冲水射流进行了观测，观察到了射流与复杂激波的碰撞和破碎。计算结果定性地显示了射流的特性。用CIP差分法研究了喷嘴形状、水柱初始位置和喷距对固体材料冲击压力的影响。

Two types of high speed water jets are examined by experimental method and numerical analysis to find effective nozzle shape. One is submerged water jet with constant delivery pressure of 50-200MPa, and nozzle diameter of 0.155 mm, the other is impulse water jet issuing from a taper nozzle into the atmosphere with velocity of 500m/s and nozzle diameter of 2mm.The main results are summarized as follows.(1) The finite difference method of CIP is effective for the numerical analysis of gas-liquid two phase flows which include discontinuous interface in the flow field.(2) In case of machining with high speed submerged water jet, the stand off distance of material from a nozzle should be taken as possible as short for piercing, drilling or cutting, because the momentum of jet plays an important role in removing material. On the other hand, the stand off distance depends on the delivery pressure for polishing or peening, because cavitation plays a main part the surface treatment. In both cases, outlet length of nozzle cap should be taken short and the diameter small.(3) On the impulse water jet which is produced by piston impact, collision and break up of the jet with complicated shock waves are observed by colored Schlielen method and high speed video camera. The computational results show the same characteristics of the jet flow as observed one qualitatively. The effect of the nozzle shape, the initial position of water column in the nozzle and stand off distance on the impact pressure on a solid material can be examined by CIP difference method.