前混合式磨料水射流磨料粒子加速过程数值模拟

Numerical simulation of abrasive particles acceleration process in pre-mixed abrasive water jet

针对前混合式磨料射流磨料加速过程运动复杂、实验研究困难及有限元处理超大变形存在网格畸变等问题,基于光滑粒子(SPH)耦合有限元(FEM)方法模拟前混合式磨料射流喷嘴不同阶段磨料粒子加速特征及磨料射流破碎靶体全过程。其中水介质用SPH建模,磨料粒子、喷嘴、靶体等用FEM建模。揭示磨料粒子群在喷嘴中的运动轨迹及喷嘴结构对磨料粒子加速影响规律。研究表明,磨料粒子进入喷嘴收敛段之前已基本达到与水介质相同速度,进入收敛段后因与水介质存在速度差使其获得加速,但与水介质速度差逐渐增大;进入直线段后水介质与磨料粒子一直加速,且水介质速度在直线段末端趋于稳定,在离开喷嘴的短距离范围内水介质速度趋于稳定,磨料粒子在核心段水流作用下继续加速,最终趋于稳定;磨料粒子群在喷嘴收敛段相互碰撞运动剧烈,进入直线段后相对平缓;流量一定下磨料粒子速度随喷嘴收敛段延长而增加,但增加有限;随直线段延长而增加,增加显著。数值模拟结果与相关文献吻合较好。

Considering the difficulties in experimental research on abrasive particles acceleration process in pre- mixed abrasive water jet（AWJ） and the mesh distortion problem in dealing with large structural deformation with finite element method （FEM）, the abrasive particles acceleration characteristics at different stages of nozzle operation and the process of target body breaking by AWJ were simulated based on an integrated algorithm of smoothed particle hydrodynamics （SPH） and FEM, in which the water was simulated by SPH, and the abrasive particles, the nozzle, the target body and so on were simulated by FEM. The abrasive particle swarm trajectories in the nozzle and the impact of nozzle structure on abrasive particles acceleration were analyzed. The results show that, the erosion pit section of the target body is ＂V＂ shaped and continues to deepen under the AWJ action. The abrasive particles have substantially reached the same speed as the water before entering the nozzle converging section. After the abrasive particles enter the nozzle convergent section, they are accelerated. However, the velocity difference between the water and the abrasive particles gradually widens. After entering the straight segment, the water and the abrasive particles are accelerated all the time, and the water velocity approaches to be steady at the end of the line segment. Within a short distance from the nozzle, the water velocity stabilizes, and the abrasive particles in the core segment of water flow continue to accelerate and finally approach to be steady. Abrasive particles collide one another violently in the nozzle convergent section, and their movement is relatively flat after entering the nozzle straight segment. Under constant flow, the abrasive particle velocity increases with the extension of the nozzle convergence section, but the velocity increases slightly. The abrasive particle velocity increases with the extension of the straight segment, but the velocity increases significantly. On the whole, the results are basically consistent with the results in relevant literatures.