33 I. Goldhirsch and G. Zanetti, Phys. 34 S. McNamara and W. R. Young, Phys. 35 G. K. Batchelor and J. T. Green, J. Fluid Mech. 36 W. Kalthoff, S. Schwarzer, G. Ristow, and H. Herrmann, submitted to Phys. We plot the product of friction factor and particle Reynolds number vs. the volume fraction .
Lines indicate the direction and amplitude of the fluid flow.
Shades of gray denote the y -component of the particle velocity, dark particles move down and light ones up. It is interesting to see that there is substantial internal motion of particles in complicated vortex patterns.