液滴撞击孔口附近壁面运动过程的模拟研究

Investigations on the process of droplet impact on an orifice plate

采用光滑粒子流体动力学(SPH)方法模拟了液滴撞击带孔壁面的问题,提出了随计算区域变化的链表搜索法.结合实验进一步研究了不同物理条件下黏性、重力和内部压应力波动对铺展过程中液滴在孔口运动情况的影响,详细分析了有限时间段内孔口断面处的压强变化.结果表明:液滴撞击表面后快速向两端铺展,到达孔口上方时形成射流,在极短暂时间内重力对射流的影响很小,但是黏性会引起射流向孔内弯曲.在内部压应力和惯性作用下射流下部产生有规律的波动,使得孔口上方流体反复的膨胀和吸收将附近应力较高区域流体吸入孔内发生孔吸现象.内部压应力是导致液滴被吸入孔内并撞击另一侧孔壁形成飞溅现象的主要原因,模拟效果和实验结果符合良好.

To investigate the process of droplet impact on an orifice plate, a two-dimensional SPH model is established. An improved linked-list search algorithm with improvement of computational domain changing with fluid is described. By analyzing the numerical results with the experimental data, influences of viscosity, gravity, and internal pressure on the spreading of droplet over the orifice are studied. It is demonstrated that spreading will change to jet flow after the droplet reaches the orifice, and then the jet will pass it rapidly and in this rather short time the effect of gravity contributes very litte to the motion. However, viscosity can induce the jet to move in a curve into the orifice. Besides, with the internal pressure and inertial effect, the lower part of the jet will fluctuate regularly. The fluctuations make the jet repeat inflation and absorption to absorb the fluid from higher pressure area, resulting in Hole Suction phenomenon. Through analyzing the pressure of the vertical section of orifice edge, we find that internal pressure plays a significant role to the droplet which is absorbed into the orifice and finally leads to splashing. Numerical results are in good agreement with the experimental data.