Experimental Study And Numerical Simulation On Water Temperature Released From The Multi-level Intake Of Large Hydropower Stations

After the construction of a large reservoir, a large area of backwater field isformed. And because of the physical chemistry characteristics of water and thefunction of the radiation of the sunlight and the atmosphere, the water temperaturedownstream which is totally different from original river is formed and the characterof the water temperature is distribution of seasonal stratification. The meaner ofbottom withdrawal from reservoir are adopted in large reservoir. But the character ofthe stratification in reservoir and the lower water temperature released will haveharmful effects on the environment downstream. And in order to satisfy the ecologicalwater in downstream, selective withdrawal is adopted gradually in the design of thehydropower station of large reservoir.Based on the multi-level intake of Nuozhadu Reservoir, this paper mainly studiedthe water temperature released from stratification reservoir via model experiment andnumerical simulation, searched the relationship of the water stratification, the heightof stop-logs gate and the water temperature released and discussed the formation ofthe water temperature released. At last this paper summed up the disciplinarian of thewater temperature released and the results provided theoretical basis for the design ofselective withdrawal in large reservoirs. The main contents and conclusions are asfollowed:(1) A review of temperature distribution and selective withdrawal was made. Theformation of the characteristics of the stratification in reservoir, the effects oflower-temperature released on the downstream environment, and the measures ofalleviation of the effects mentioned above was introduced, and the method ofprediction and experiment was also presented.(2) Similarity relationship of water temperature experiment for selectivewithdrawal from reservoirs was analyzed. Based on continuity equation, motionequation and heat balance equation, and considering the flow features of selectivewithdrawal the similarity relationship of water temperature experiment was analyzed.In the condition of the geometry similarity, ensure the the equality of Froude numberand density Froude number in the reservoir of prototype and experiment respectively.And the relationship for conversion of water temperature between model andprototype had been proposed. And the results were consistent with those in prototype. (3) A model experiment was conducted based on multi-level intake in NuozhaduHydropower station, by heating up water directly to realize the thermal stratificationin reservoir. The water temperature released was gained via the experiment, and thevariations of the water temperature released were analyzed. On the condition of thefixedness of the water temperature distribution and water level, the variety of thewater temperature released with the height of the stop logs gate was studied; on thecondition of different water temperature distributions, the relationship of the increasescope of the water temperature released and the water temperature distribution wasdiscussed; and on the condition of the same submerge depth, the water temperaturereleased also was analyzed.(4) An comprehensive introduction of the Flow-3D model was made in the paper,and based on the model a refined3-D intake model was established to simulate theselective withdrawal. And the model results had a good agreement with that in theexperiment. The flow characteristics near the intake in case of thermal stratificationwere analyzed via the comparison of the thermal stratification and homogeneoustemperature in reservoir. The temperature field and flow field near the intake weregained. And the formation of the water temperature released and the position of thewater temperature released in the thermal stratification were analyzed.