基于改进的低雷诺数湍流模型的软性磨粒流加工仿真与实验

针对模具结构化表面软性磨粒流精密加工中壁面特性求解困难的问题，基于改进的低雷诺数湍流模型提出了一种对软性磨粒流壁面特性进行分析的方法。该模型仿真的湍流可以从充分发展的高雷诺数湍流到低雷诺数湍流，所以，对于壁面区域的求解精度更高。以机械加工中常见的U形沟槽为仿真对象，数值模拟了其内部流场，尤其是壁面区的流场特征参数。分析结果表明:当初始压力p0在2.5～4.5MPa之间时,流道的内部流动是不完全发展的湍流,详细分析了p0为4.5MPa时渐变截面流道的内部流动,压力与速度分布均是中心高、两侧低,而且越靠近U形底部,压力值和速度值越高;磨粒流速度一直增大,磨粒受到的驱动力增大,使得单位时间内颗粒与壁面的碰撞增加。通过碰撞观测实验发现磨粒对壁面的碰撞速度与仿真结果相符，加工实验进一步验证了仿真结果。

Simulation and Experiment of Soft Abrasive Flow Machining Based on Improved Low-Reynolds-number Turbulence Model

To solve the difficulty in simulating flow characteristics,especially characteristics near the wall,during the precise soft abrasive flow machining of  the structural surfaces of molds, a method based on improved low-Reynolds-number turbulence model was proposed herein. This improved model could simulate turbulences of both high and low-Reynolds numbers, thus had  higher simulation precision for the wall regions.U-shaped groove, a common machining workpiece, was selected as the object of the simulation. In the experiments,the internal flow field of the U-shaped groove, especially the flow characteristics near the wall, was simulated numerically. The analyses show that when initial pressure p0 is in the range of 2.5MPa to 4.5MPa, the internal flow is incompletely developed turbulence. The internal flow when p0 is 4.5MPa is analyzed in detail. It is found that in the flow path, both the pressure and velocity are higher at the center and lower on sides. In addition, pressure and velocity are higher in regions closer to the bottom of the U-shape. As the velocity of the abrasive flow increases, the driving force on the abrasive particles also increases, thus more particles collide with the wall per unit time. The collision experiments demonstrate that the abrasive particles' velocity of collision with the wall calculated by simulation is in accordance with the experimental data,and the machining experiments further validated the numerical simulation results.