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Experimental study of sand jet front in water

Profile image of Amir AzimiAmir Azimi

2012, International Journal of Multiphase Flow

https://doi.org/10.1016/J.IJMULTIPHASEFLOW.2011.11.008
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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.

FAQs

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What parameters affect the hydrodynamics of particle-laden jets in water?add

The study finds that nozzle diameter, particle size, and concentration significantly influence the hydrodynamics, with the normalized buoyancy effect being crucial, especially when values exceed 0.1.

How does particle size influence the frontal velocity of sand jets?add

Results show that larger particles increase frontal jet velocities, achieving ratios of up to 5 times their settling velocity, particularly evident at distances greater than x/d = 200.

What are the regimes observed in the evolution of particle clouds?add

The experiments categorize particle cloud behaviors into thermal, bowl-shaped swarms, and narrower penetrative clouds based on Reynolds numbers varying across critical thresholds around Re_p = 10.

How is turbulence modulation affected by particle concentration?add

The analysis reveals that turbulence attenuation is more pronounced with smaller particles, exhibiting quicker energy dissipation due to lower Stokes numbers, directly impacting flow stability.

Which techniques were used for vortex extraction in the experiments?add

Vortex structures were identified using Galilean decomposition and swirling strength methods, revealing correlations between particle size and vortex characteristics across varying Reynolds numbers.

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