Laboratory Study on the Entrainment Process in Overflow

Abstract

During the sinking process, overflow generates an entrainment phenomenon, accompanied by the occurrence, development, and dissipation of vortices. In this paper, particle image velocimetry (PIV) technology is used to measure the flow fields of overflow sinking, invasion, and mixing. In order to quantitatively analyze the mixing and flow processes during the sinking of the overflow, vorticity, turbulence dissipation, Froude number, local Richardson number, and entrainment coefficient are calculated. In a stratified environment, the overflow entrains the environment fluid of lower density to reach a terminal height where their density equals that of their surroundings and then spread out horizontally. The experimental results show the terminal depth is related to the density of the overflow. The lower the density, the smaller the terminal depth. The turbulent dissipation mainly occurs in the area along the slope and during the process of invading flow to the surrounding. The extreme of the turbulent dissipation is corresponding to the maximum velocity shear and vorticity. At the point where the overflow crosses the sill and at the front end of the overflow, there will be a more obvious phenomenon of entrainment. The entrainment parameter is positively correlated with the density of overflow. These preliminary results would require additional experimental validation and data observation in order to assess their relevance for realistic flow regimes.