EFFECTS OF PARTICLE ARRANGEMENTS ON THE DRAG FORCE OF A PARTICLE IN THE INTERMEDIATE FLOW REGIME

The drag force of a single particle in the presence of other equal-siz ed particles arranged in specific configurations is measured directly for Re from 30 to 106. Four particle arrangements are investigated: a two-particle configuration (Model I), a three-coaligned particle confi guration (Model II), a hexagonal particle configuration (Model III) an d a cubic particle configuration (Model IV). Variables studied include the particle Reynolds number (Re) and the separation distance. The ef fect of pipe wall on the measurement results is also examined. The mea sured drag force, expressed in terms of the drag ratio, is compared wi th the theoretical values at zero Re and the experimental values for 1 00 < Re < 10(3) reported in the literature. Comparisons of the experim entally determined drag ratios with numerically simulated values are a lso conducted. Because of the Re effect, the drag ratio curves for Mod el I are no longer symmetrical with respect to theta = 90 degrees as o bserved for the Stokes flow. The results for Model I at theta = 90 deg rees show that the drag ratio increases with the separation distance a nd then decreases with further increasing separation distance, and the combination of the Re and wall effects causes the drag ratios higher than unity. For Model II, the drag ratio of the middle particle is low er than that of the upper particle at small separation distances but b ecomes slightly higher beyond a certain separation distance, The compu tational results provide detailed information on the flow field around each particle, and the pressure and the shear stress distributions on particle surfaces. The numerically simulated drag ratios compare reas onably well with the experimental data. The drag ratio behavior for Mo del IV is found to be similar to Models I and III; however, the Re doe s not seem to affect the drag ratio. The results of the flow visualiza tion conducted in this study dearly demonstrate a significant change o f the wake structure of Models I and III at different separation dista nces.