Mixing of Twin Particle Clouds in Stagnant Water

Abstract

The interaction and mixing of twin particle clouds in stagnant water were studied by a series of laboratory experiments. The importance of source separation distance and sand particle mass was investigated by introducing nondimensional parameters. The frontal positions of twin particle clouds were compared with the corresponding single particle cloud frontal positions and a critical source separation distance was reported based on the maximum frontal velocity and minimum mass loss of twin particle clouds. The maximum frontal velocity of the critical twin particle cloud was found to be correlated with the depletion of the ambient entrainment in a region between the two clouds. The maximum cloud width took place in nondimensional time of t/T=0.5 and the boundary depth between thermal and swarm regimes in twin particle clouds occurred in t/T=1.4 irrespective of the initial condition of the clouds as well as source separation distances. In twin clouds with the large mass of sand particles, the swarm width of twin particle clouds became 1.5 times larger than that of the corresponding single particle clouds. The maximum centerline velocity inside the twin clouds occurred once the source separation distance became five times the nozzle diameter. The radial velocity variations inside the twin clouds showed a 30% higher time duration, indicating that the trailing part of a single particle cloud remained longer in the water than the twin particle clouds. The entrainment coefficient attenuated by increasing the aspect ratio of particle clouds and an empirical equation was adopted for prediction of the entrainment coefficient. The turbulent intensity of particle clouds was assessed and it was observed that the velocity fluctuations were higher in closer distances from the nozzles in larger aspect ratios.