Experimental study of sand jet front in water

Abstract

An experimental study was conducted to examine the behaviour of a sand jet front in water and its associated fluid motions with different sand particle sizes and initial sand jet diameters. The shape of sand jet front was found to be directly related to the particle Reynolds number of sand particles. The frontal velocity along the centreline of the jet axis was measured and compared to that of single-phase buoyant jets and particle thermals. The jet front settling velocity of small particles was found to be as large as 5 times that of the individual particle settling velocity. The presence of particles and the additional momentum generated by particles were found to reduce the growth rate of the jet front width, compared with those of the single-phase buoyant jets and particle thermals. Evolution of vortices and their structure were extracted from velocity fields by employing Galilean velocity decomposition and a local vortex identification technique. It was shown that, radial convection velocity can change the shape of the vortices. Large radial convection velocity transformed the vortex from semi-circular shape to elongated ellipsoid vortex. Effect of particles on turbulence of the carrier phase was studied. It was found that smaller particles increase turbulence attenuation of the carrier phase. Effect of particles on the modulation of turbulence can be described by the Stokes number along the jet axis. A classification was made for solid–liquid and solid–gas turbulent jets and new formulations were proposed to show the correlation between Stokes number and the turbulence attenuation of particle-laden turbulent jets.