Study On The Water Temperature Prediction Model For The Huge And Deep Reservoir

The water temperature prediction for the huge and deep reservoir is one of the important contents of the environmental impact assessment on the hydropower projects. It is greatly meaningful to sustainable development of water resources. Based on the previous studies, the 2-D laterally averaged temperature model for the temperature prediction of the huge and deep reservoir is developed in this paper. In the mean while, the movement mechanism of the turbulent buoyant flow in reservoir and the rule of the thermal stratification forming, developing and varying are probed. The model is then applied to the huge reservoir of Xiluodu on Jinshajiang River and the cascade power stations on Yalongjiang River. The main contents and conclusions of the study are as followed:1, According to the experiment data of the gravity flow in reservoir, the accuracy and economy of RSM (Reynolds Stress Model), k-s model and Spalart-Allmaras model are compared. The results show that RSM can accurately simulate the movement of the turbulent buoyant flow in reservoir and the anisotropic turbulence due to the thermal stratification. However, RSM is difficult in convergence, bad stability and more time consuming. RSM is suitable when the high accuracy is concerned and geometry boundary is simple. The movement feature of the gravity flow computed by the k-s model is identical with the measurement. It obviously has higher accuracy than the previous models but lessthan RSM. The k-e model is a good alternative approach when the flow or geometry boundary is complicated. Spalart-Allmaras model is not suitable to simulate the buoyant flow in reservoir.2, Application of the modified k-e model by Munk-Anderson equation to gravity flow in reservoir shows that the modified model overestimates the turbulent intensity in reservoir. It results enhance of momentum exchange in vertical direction and large error in velocity. Author considers that Munk-Anderson's modification is not suitable to simulate the buoyant flow in reservoir, and suggests the turbulent Prandtl number as the constant of 0.85 in the water temperature model of reservoir.3, Based on the standard k-s model, the laterally-averaged 2-D buoyant flow model to predict the water temperature of the huge and deep reservoir is developed. This model is succeeded in verification by the field data obtained from Ertan reservoir. It shows that the model can accurately simulate the thermal stratification formation and development. It is well feasible for engineering purposes. The parameters of 1 and , which is needed to calibrate, only appreciably influence the water temperature of 10 meters depth under the waer surface. It has little influence on the whole temperature structure of the reservoir with 100m deep and no influence on the outflow temperature.4, It has shown, through the study on the temperature modeling of Ertan reservoir, that the location of upstream boundary can not be placed on the section with a great temperature gradient in vertical, because the water temperature distribution at upstream boundary can control the temperature structure in reservoir. The velocity and the temperature at upstream boundary are not matched, and this will lead to great errors.5, The 2-D laterally-averaged reservoir model is used to predict the water temperature of the huge reservoir of Xiluodu. The results show that the thermal stratification exists during the time of whole year. The water temperature difference in vertical is lowest in February with 2 and is largest in June and July with 13 . In October and November, the cold water on surface settles down and strengthens the vertical mixture. The inflow dives down to the bed. So the temperature near thebed reaches the maximum of 16 in a year. The water temperature varies in a range of 4 near the bed and 10 on the surface. It is found, through further study on the water temperature distribution in the high flow year, the low flow year and the cold year, that the influences of discharge and weather are limited on the water tem...