On the effect of gravitational and hydrodynamic forces on particle motion in a quiescent fluid at high particle Reynolds numbers

Abstract

Trajectories of 5 and 10 mm metallic and plastic particles in a quiescent liquid during their sedimentation toward a plate were studied using experimental and numerical means, and the influence of gravity, drag, added mass, and history forces were evaluated. Variations of particle diameter and density allowed measurements at Reynolds numbers, based on the impact velocity, in the range of 1 000 to 13 000. A computer model was developed and the Lagrangian equation of particle motion was solved. The results showed that the combination of gravity, drag, and added mass forces are important for the simulation of the motion of small particles for the duration of their flight from the starting point to the wall impact, in the range of particle Reynolds numbers between 1000 and 5000. Comparison of the simulation results with the data showed that the predicted trajectories underestimated the experimental observations by about 1% to 4.3%. When the history force was included in the governing equation, however, excellent agreement between the measured and predicted particle trajectory was obtained. Experimental results for the motion of large particles showed oscillations in the time history of particle velocity when the particle Reynolds number was in the range of 3 000 to 13 000. Repeating the experiment, and averaging the data of a large number of experiments, yielded averaged curves for the particle velocity that did not show oscillatory values. In this case, good agreement between numerical and experimental data was observed. The study also shows that at high particle Reynolds numbers, the effect of the history force becomes negligibly small.PACS No.: 47.55kf