Numerical prediction of particle trajectories in an erosion experiment
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摘要: 针对冲击磨损实验研究中磨粒群体的运动轨迹难以准确表征的问题，在负压喷射砂粒群冲击Q235钢板的实验中宏观测量了砂粒撞击的速度与位置分布，并使用数值方法模拟了实验砂粒与空气在喷嘴内外的双向耦合过程，以实现负压喷射砂粒群的轨迹预测。计算中提出了非球形粒子在相对马赫数接近1时的曳力模型，以反映空气可压缩引起砂粒表面流动分离的现象，并合理选择Magnus升力模型及壁面反射模型，最终数值预测的砂粒碰撞速度以及撞击位置与实验情况吻合良好。Abstract: It is necessary to study the erosive wear caused by conveying granules, but it is difficult to track particles trajectories which are required for erosion prediction, especially in shot blasting experiments. In an erosion test, marine sand grains are ejected from a sand-blasting gun and impact Q235 steel plate. The impinging velocities and impinging locations of the sand grains with different inlet air pressure are measured statistically. The two-way coupling process inside or outside the blast nozzle between sand grains and high-speed compressible air are numerically simulated to numerically describe the trajectories of particles. In this simulation case, some approaches are studied and compared with the experimental results. Considering the influence of compressible air on the boundary flow separation of the sand, a new drag law, for the case that the relative Mach number of irregularly shaped particles is approximate to 1, is proposed by making drag coefficient change with the relative Mach number. Local slopes, the angle of which is random, are assumed on the wall to simulating the rough wall rebound effect. The mean value of the slope angles is 0º and the standard deviation is 20º. Magnus lift force is also integrated into the numerical simulation to enlarge the jet angle of particles and make the erosive scar larger. By combining the nonpherical high Mach number drag law, rough wall model and Magnus lift force model, the simulation achieves satisfying result, in which the velocity magnitudes and impinging location distribution of particles agree well with the experimental data. It indicates that the particles trajectories in simulation are also roughly coincident with the real ones in experiment. This work proves tracking approaches affect the particles trajectories significantly and provides a valid tool to summarize and verify the erosion formula or to predict erosive wear.
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图 1 气驱砂冲蚀磨损实验装置示意图
Figure 1. Diagram of the air-blasting-sand erosion experimental setup
图 4 不同曳力模型得到的平均喷砂速度与实验值比较
Figure 4. Comparison of blasting sand speeds between numerical and experimental results
图 5 实验冲蚀痕迹与光滑壁面且忽略升力的数值结果对比
Figure 5. Comparison between experimental and numerical results (smooth wall & no lift force).
图 6 粗糙壁面模型对冲蚀数值结果的影响
Figure 6. The rough wall model effects on numerical erosion results
图 7 非球形高Ma曳力，粗糙壁面与升力的联合模型下的气相速率度与部分颗粒轨迹数值解
Figure 7. The numerical results of air velocity magnitude and some particle trajectories by the combined model
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