中斯托克斯数载粒子射流速度演变实验分析

Experimental analysis of velocity evolution in moderate-Stokes-number particle-laden jets

关键词:  射流  中斯托克斯数  速度场  粒子图像测速（PIV）  衰减

Key words:  jet  moderate-Stokes-number  velocity field  particle image velocimetry（PIV）  decay

摘要:

为系统全面地理解中斯托克斯数载粒子射流（MSPJ）的动力学特性,并验证泰勒流体粒子理论在更小粒子情况下的适用性,开展了中斯托克斯数载粒子射流速度演变实验分析。首先,搭建了粒子图像测速（PIV）实验台。其次,分别进行了6组不同初速度下的宏观大尺度与介观尺度测量实验。最后,进行了两种尺度下粒子的瞬时速度、平均速度和脉动速度的演化规律对比分析,并结合泰勒流体粒子理论模型对MSPJ速度衰减进行了预测和验证分析。结果表明:沿射流中心线的粒子平均速度衰减趋势与气相相似,呈现出先增大后减小的趋势；而由于壁面反弹的低速粒子与射流中心的高速粒子混合,粒子脉动速度的衰减显著不同,呈现出先减小后增大再减小的趋势。此外,喷嘴附近的粒子脉动速度场与平均速度场的分布存在显著差异,脉动速度场表现为中间速度较小、边缘及过渡区速度较大的分布特征,平均速度场则相反。泰勒流体粒子理论对MSPJ粒子速度衰减预测的最大累积误差为6.16%。重粒子的速度自相似性因明显的惯性效应而更快衰减。本研究能够为滑移速度、曳力及发动机油液喷雾等相关领域的进一步研究提供参考。

Abstract:

To systematically and comprehensively understand the dynamics of the moderate-Stokes-number particle-laden jet (MSPJ) and to verify the applicability of Taylor’s fluid particle theory for smaller particles, an experimental analysis of the velocity evolution of moderate-Stokes-number particle jet is carried out. Firstly, a particle image velocimetry (PIV) experimental bench is built. Then, six sets of experiments including macroscopic large-scale and mesoscale measurements are carried out at different initial velocities. Finally, the evolution characteristics of instantaneous velocity, average velocity and fluctuating velocity of particles at two scales are compared and analyzed, and the MSPJ velocity decay is predicted and verified by combining with Taylor’s particle-laden fluid theory model. The results indicate that the average velocity of particles along the jet centerline decays similarly to the gas phase, exhibiting an initial increase followed by a decrease. In contrast, due to the mixing of low-velocity particles rebounding off the wall and high-velocity particles in the center of the jet, the attenuation of particle fluctuating velocity exhibits a different trend: it first decreases, then increases, and finally decreases again. Moreover, a significant difference is observed between the distributions of the particle pulsating velocity field near the nozzle and the average velocity field; the fluctuating velocity field displays a profile characterized by lower velocities in the center and higher velocities at the edges and in the transition zone, while the average velocity field shows the opposite pattern. The maximum cumulative error of Taylor’s fluid particle theory in predicting MSPJ particle velocity attenuation is 6.16%. Additionally, the velocity self-similarity of heavy particles decays more rapidly due to significant inertial effects. This study provides a reference for further research in the areas of slip velocity, drag force, and engine oil spray.