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

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.