三峡工程坝身泄流下游水体溶解氧浓度数值模拟

三峡工程坝身泄流与下游水体强烈碰撞,产生大量气泡,当气泡渗透进入水体一定深处时,气泡界面与水体之间的质量交换极易导致水体溶解气体浓度超饱和,可导致鱼类气泡病.该文应用气泡界面传质理论建立了掺气水流的溶解氧浓度对流扩散方程,与气液两相流混合模型相耦合,模拟计算了三峡大坝在库水位为139m情况下溶解氧浓度变化情况,成功地与现场观测数据进行了验证,完善了气泡界面传质系数公式.对关键因子进行敏感分析,表明气含率、紊动强度、下游水深是决定溶解氧浓度的关键因素.

Numerical simulation of dissolved oxygen concentration in the downstream of Three Georges Dam

Strong colliding between the water flow discharged from spillway and the water-body in the stilling basin will produce a lot of air bubbles in the downstream of the Three Georges Dam. Bubble mass transfer will be dominant and can cause total dissolved gas (TDG) supersaturation. Elevated TDG level has a negative effect on aquatic organisms in the form of gas bubble trauma (GBT). Dissolved oxygen (DO) transport model was developed in this paper and used to simulate the physical processes of gas transfer coupled with the air-water two-phase mixture flow model. Supersaturated DO concentration in the water-body downstream was successfully calculated during spillage when the water level is 139m in the Three Georges reservoir. Sensitivity analysis showed that the gas void ratio at plunge point, the turbulence intensity and tailwater depth are the most dominant factors in determining DO concentrations.