两相流振荡换热过程数值模拟分析

为深入了解振荡条件下的两相流运动过程与流动换热特性,采用数值仿真研究方法,摒弃活塞复杂的结构因素,以简化模型为研究对象,从基础问题出发探索各因素对两相流振荡换热过程的影响。通过一系列的数值模拟,直观地展现了油腔内两相流运动过程是高度紊乱的不对称流动。研究结果表明:除活塞二阶运动产生偏离外,油腔上下运动引起的压力变化也将引起油柱倾斜,造成喷油与油腔入口偏离;活塞运动产生的强制振荡是影响腔内流动换热波动的决定性因素,油腔表面传热系数、填充率等的波动频率都与活塞运动频率完全吻合。此外,研究还发现喷油速率、活塞转速等参数对填充率和传热系数都会产生显著的影响,但这些影响因素可能并不是单一作用而是相互耦合的。喷油油柱在进入油腔时的速度与活塞的最大运动速度之间的匹配度可能是影响油腔填充率及传热系数的一个关键因素;当喷油的绝对速度与活塞最大速度接近或大于活塞最大速度时,将达到较为理想的填充率和传热系数。

Numerical Simulation of Two Phase Flow Oscillation Heat Transfer Process

A two-dimensional simplified model was used to explore the influence factors of two phase flow oscillation heat transfer process in a oil chamber. Through a serious of numerical simulation, it is shown that the two phase flow in the oil chamber is a highly disordered asymmetric flow. In addition to the two order motion of the piston to produce the oil injection deviation, the pressure fluctuation caused by the movement of the oil plume up and down will also make the oil plume tilted, causing the spray to deviate from the chamber inlet. According to the study, the compulsory oscillation caused by the piston motion is a decisive factor to influence the oil flow and heat transfer characteristics in the chamber. The fluctuation frequencies of the filling ratio and surface heat transfer coefficient are fully consistent with the piston motion frequency.Moreover, the fuel injection rate and the piston speed have a significant effect on the filling ratio and heat transfer coefficient, but these factors may not be a single effect but mutual coupling. The matching degree of the spray velocity into the oil chamber and the maximum piston speed may be a key factor to influence the filling ratio and heat transfer coefficients. When the spray absolute velocity is close to or greater than the maximum piston velocity, the ideal filling ratio and heat transfer cofficient will be achieved.