Dynamics of Crystalline Gravity Currents
Shahidi, Amir Etemad
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Gravity currents, which are also known as density currents, are established when one fluid flows into another of different density, and the density difference between the two drives the flow. They are widespread and vital phenomena that occur within numerous natural systems (Lemckert and Imberger, 1993a, b; Lemckert et al., 2002; Yu et al., 2013; Zigic et al., 2002). While the majority of commonly occurring gravity currents have received significant attention by researchers, crystalline gravity currents have not been studied extensively yet, and there is very little fundamental knowledge about their behavior. Crystalline and particle-driven gravity currents are suspensions of dense particles that spread into an ambient fluid due to the difference between the density of suspension and that of the ambient fluid (Sparks et al., 1997; Simpson, 1997). Studies have been conducted in laboratories analyzing gravity currents mainly on lock exchange phenomenon (Huppert and Simpson, 1980; Hallworth et al. 1996; Lemckert et al., 2002; Rottman and Simpson, 1983; Shin et al., 2004) and continuous inflow phenomenon (Ellison and Turner, 1959; Garcia, 1993; Maxworthy, 1983; Middleton, 1966b; Zhang et al., 2008). In Lock exchange mechanism, two fluids of varying density are kept separate by a lock gate. The fluid with higher density is known as the lock fluid and it has significantly lower volume than the second fluid. When the lock gate is removed, gravity current forms because of the density difference between the fluids. During the evolution of the current, the particles continually deposit or dissolve, thus reducing the excess density of suspension and the driving buoyancy force (e. g. during the late stages of turbidity currents, Parker et al., 1986). While the non-dissolving kind (sediment-laden) is well studied by many researchers (Fragoso et al., 2013; Garcia, 1994; Hallworth et al., 1996; Kuenen, 1937; Parker et al., 1986; Simpson and Britter, 1979; Shin et al., 2004;), the crystalline gravity currents are not being looked at. The focus of this study was on these currents produced by lock release inflow of highly saline solution with suspended salt crystals to understand their behavior, and the impact they may have on the receiving environment. The results were then compared with those of unsaturated gravity currents under the same experimental conditions. Data were also extracted from the literature for sediment-laden lock release gravity currents under similar experimental conditions and compared with the findings of this study focusing on the self-similar phase. The outcomes of this experimental study showed that dynamics of crystalline gravity currents are entirely different from those of unsaturated and sediment-laden gravity currents. The temporal change in the driving buoyancy affects its characteristics. The research and outcomes of this study will assist in providing first-hand knowledge of the progress of gravity currents with initially suspended salt crystals in lock release condition into a receiving environment.
Master of Philosophy (MPhil)
School of Eng & Built Env
The author owns the copyright in this thesis, unless stated otherwise.
Crystalline gravity currents
Unsaturated and sediment-laden gravity currents
Particle-driven gravity currents