Effect of thermal stratification on interflow travel time in stratified reservoir

Abstract

This study is focused on the impact of thermal stratification on interflow travel time. A quantitative relation between buoyancy frequency and interflow travel time is theoretically derived based on the Bernoulli principle of energy conservation. Experiments and numerical simulations are carried out to validate the applicability of the proposed relation. For experiments, interflow movement is successfully detected in a small-depth water tank by releasing a denser flow into a temperature stratification environment. For numerical simulations, a vertical 2D renormalization group (RNG) k- model is developed to simulate the interflow. The results both of the experiments and of the numerical simulations verify our proposed theory. The derived analytic relation is useful for the prediction of contaminant travel time in reservoirs and in assisting pollution control.

Impact of revised thermal stability on pollutant transport time in a deep reservoir

“…14a), implying that higher temperature (stronger stratification) generally promotes water exchange in the study reservoir in summer. This was also consistent with the relationships observed for interflow (Ahlfeld et al, 2003;Zhang et al, 2015), which indicates that the flow patterns of Hongfeng Reservoir during summer may be dominated by interflow; however, overflow and underflow appeared at certain times in some areas. Additionally, although S 2 was much higher than S 1 and S 3 , the slopes of relationship between stability and water age were very close, implying the consistent effects of stratification (reflected by S 1 , S 2 or S 3 ) on water age.…”

“…Inversely, the water age for the middle and bottom layers distinctly declined with increasing air temperature, especially for R2 and R3. This might be explained by the decreasing intrusion thickness of interflow or underflow with stronger stratification, leading to a higher velocity and a shorter transport time (Ahlfeld et al, 2003;Zhang et al, 2015). For the balance of the whole system, the slower flow of the surface layer with higher air temperature was also reasonable.…”

“…The pollutant transport process in a deep reservoir is highly influenced by thermal stratification, especially when the contaminated inflow acts as interflow (Ahlfeld et al, 2003;Zhang et al, 2015). An inverse relationship between thermal stratification (indicated by stratification number, vertical temperature difference or buoyancy frequency) and interflow travel time (defined by a certain percentage of tracer concentration) has been determined by analytical analyses, laboratory experiments or numerical simulations by many researchers (Gu et al, 1996;Chung, 1998, 2003;Ahlfeld et al, 2003;Zhang et al, 2015).…”

“…An inverse relationship between thermal stratification (indicated by stratification number, vertical temperature difference or buoyancy frequency) and interflow travel time (defined by a certain percentage of tracer concentration) has been determined by analytical analyses, laboratory experiments or numerical simulations by many researchers (Gu et al, 1996;Chung, 1998, 2003;Ahlfeld et al, 2003;Zhang et al, 2015). Due to the difficulty of calculating the transport time at any site, few studies have addressed the thermal stratification effect on the transport process at different depths in a reservoir with complex flow patterns.…”

Experimental Investigation of Separation Angle of Interflow Dense Current from Bed

“…The results of simulation showed that if the concentration of turbidity fluid exceeds 2000 mg/L, the river flow can be formed as an interflow in the summer months. Zhang et al, (2015) investigated the effect of thermal stratification created in a reservoir on the travel time of the pollutant interflow; they simulated the leakage of the pollutant into the reservoir through sudden diffusion of a stream into a stratified reservoir and predicted the interflow velocity through dimensional analysis based on the energy conservation law and eventually provided a linear relationship between the travel time and buoyancy.…”