Suspension and turbulence modification effects of solid particulates on a horizontal turbulent channel flow

Abstract

Experimental measurements detailing the turbulence modification and suspension mechanism of particulates within a horizontal solid/liquid channel flow are presented. The measurement technique utilized a simultaneous two-phase particle image velocimetry method to examine the instantaneous particle-fluid structure, and to acquire correlated particle-fluid statistics to describe the two-way coupling between the phases. The results show that the presence of the particles distinctly alters the mean fluid motion, even though the bulk mass loadings are only on the order of 10⁻⁴. The carrier phase turbulence properties are also altered, showing an effective increase in the wall friction velocity of approximately 7%, and an increase of the normal and shear Reynolds stress by approximately 8-10% in the outer flow (y/h > 0.1). The particles in the flow exhibited a lag in the mean streamwise velocity, while the local streamwise slip velocity in the vicinity of the particle was found to be near negligible levels. In contrast, the mean vertical velocity of the particles matched the fluid, but exhibited a local slip velocity of approximately 40% of the expected particle settling velocity in the outer regions of the flow.

The cause of the mean slip velocity in the streamwise direction was shown to be primarily the organization of the upward moving particles into the Q2 ejection events of the flow, and not a purely stochastic gradient transport process. The downward moving particles, however, exhibited little evidence of preferential organization between the Q3 and sweep (Q4) events, resulting in the particles moving within fluid regions which had a speed similar to the overall mean fluid velocity. The structures found to be primarily responsible for this interaction consist of vortex packets similar to those identified by Adrian et al (2000 J. Fluid Mech. 422 1-54), with the particles being ejected upward beneath the ‘head’ of the concentrated vortex, within a region of the dominant Reynolds stress contribution. In addition, spanwise counter-rotating structures were also found in the flow, which appeared to eject particles in the induced flow region between the two cores.

This article was chosen from selected Proceedings of the Second International Symposium on Turbulence and Shear Flow Phenomena (KTH-Stockholm, 27-29 June 2001) ed E Lindborg, A Johansson, J Eaton, J Humphrey, N Kasagi, M Leschziner and M Sommerfeld.

Present address: Science Systems and Applications, Inc., Lanham, MD 20706, USA.

Notes

Present address: Science Systems and Applications, Inc., Lanham, MD 20706, USA.