EFFECTS OF TURBULENCE ON DRAG COEFFICIENTS OF SPHERES IN A SUPERCRITICAL FLOW REGIME

Drag coefficients of aerodynamically smooth spheres varying in diameter from 0.0625 to 1.004 in. and in density from 0.195 to 7.80 g./cc. were obtained at acceleration rates ranging from 120 to −30 ft./sq.sec. The particles were subjected to relative turbulence intensities of 7 to 35% and to ratios of Eulerian macroscale to particle diameter of about 0.4 to 5. Quantitative measurement of particle drag coefficients was made possible by the use of a new particle tracing technique which permits the resolution of time to the nearest tenth of a millisecond. The resulting data extend farther into the supercritical flow regime than any other measurements previously reported. The variation in drag coefficient with Reynolds number indicates a continuous alteration in the flow pattern around a sphere in this region. The effect of turbulence is, essentially, to increase supercritical drag, although this effect was found to diminish with increasing Reynolds number. Possible mechanisms for the effects of Reynolds number and turbulence on the particle drag coefficient are suggested. Copyright © 1969 American Institute of Chemical Engineers