Simulation Calculation Of Hydralic Problems In Hydropower Station And Its Application In Engineerings

There are numerous problems involved the hydraulics in the construction of a hydropower station, this paper focuses research on the basic theory and calculation method which involve the wave surge in hydraulic transient process of the long diversion channel, tail water dredging of the riverbed, hydraulic transition process of the long tail water or diversion pressure tunnel (pipe) in the hydropower station, meanwhile having been applied in practical engineerings.Based on the physical model test which is verified by the numerical simulation technology, the simulation researches on the unsteady flow in an open channel are carried out by using the examples of Hengdan Hydropower Station which is located in Bailong River and Xueka Hydropower Station in Tibet when they are in the planning design stage.The calculation method is focused on the natural river's water surface under the condition of complex terrain. The studies on the tail water dredging in Yangqu Hydropower Station are optimized under considering the mainly optimum results in different influence of dredging under different backwater elevation of Longyangxia Reservoir which located in the Yellow River.Finally the simulation for transient flow of the long diversion channel in the hydropower station is made and the result is applied in the analysis and study for Hengdan Hydropower Station and Xueka Hydropower Station. At the same time, through the comparative analysis with the results of model experiments, the simulation calculation for hydraulic transition process is used in the large and middle hydropower stations. The main conclusions are as follows:(1) The simulation study on the wave surge of the long diversion channel in Hengdan Hydropower Station shows that the overall design is reasonable. The suggestion is proposed that the channel bottom elevation should be declined 0.5 m for meeting the design flow of 161.8m~3/s during normal operation and canceling the side weir project. The comparison between the hydraulic transient calculations and ministerial specification formulas under four machines working conditions are made in the simulation calculations for Xueka Hydropower Station.The water surface profiles under the normal condition and the highest level in impoundment pool are calculated under four machines working conditions by using the ministerial specification formulas, and the fluctuation envelopes including the highest water level and lowest water level from hydraulic transient calculation are more suitable to describe the movement of water flow, that is to say, they are more accordant with the characteristics of water flow movement. Many parameters such as the flow of channel inlet, overflow flow line of siedweir, channels'transient surface lines, and the spread and reflection processes of the upstream and downstream wave surge could be provided by hydraulic transient simulation, at the same time, compared with design code, more information could be provided, and more reasonable description could be made for unsteady flow movement.(2) The simulation calculation model for complete one-dimensional steady non-uniform flow could better accord with the flow movement rules under natural irregular topography, not only taking into account the width and elevation changes in both upstream and downstream section, but also reflecting the alongshore and local head loss, so the result should be more close to the actual project.Based on the prediction - correction solving method, the simulation calculation model for complete one-dimensional steady non-uniform flow, and the criterion formula for uniform flow depth and critical water depth, the continuity for water surface profile calculating could be resolved better under the complex terrain conditions with plus slope and adverse slope alternating and with sudden expansion and sudden contraction occurring frequently in compound section rivers. The results of the computation should be closer to reality.For the roughness coefficient of complicated terrain , the roughness coefficient should be preset firstly, Here, by using the prediction - correction method to calculate many times repeatedly, the roughness coefficient of Yangqu Gorge to Yehu Gorge is determined as 0.04 and that of Wutuo Basin is determined as 0.03. Now the water surface lines from calculation and observation are identical well, the roughness coefficients determined here are also accordant with engineering specifications and technical personnel's experience. The water surface lines from calculation results show that although the maximum error between the calculation and observation individual sections would be 0.54 m, but in most sections, the error of the water level should be less than 0.4 m, the error could meet the accuracy for engineering design.Through the application of one-dimensional steady non-uniform flow calculation model, the plan of two different dredging lengths are proposed, and the research is focused on the dredging effects for dredging being 3472 m, slopes of river for 0.05%, 0.1%, 0.15%, dredging widths being 50 m, 80 m, 140 m. Eight sets of dredging plans are combined, and the water surface lines under various flows and the water level ~ flow relations in characteristic sections are forecasted respectively.The recommended excavation programâ…¡( -0.05% -50 m) is got by comprehensive analyses, the width is 50 m and slope is 0.05%, and the amount of excavation works is 1,231,900 m~3 from the end of the excavation to the import of Yehu Gorge. Now under the average flow of 625.0 m~3/s in the recommended program, the tail-water level of the workshop is declined from 2 595.49 m to 2 590.34 m before and after the excavation, reducing 5.15 m. Along with the increase of the flow, the tail-water level of the workshop is reduced smaller and smaller, and when the flow is more than 2 500 m~3 / s, the tail-water level of the workshop is hardly decreased after the excavation.For the given water level before Longyangxia dam, there are the corresponding water level ~flow relation curves in Yehu Gorge. Aiming at each water level before the dam and with the water level ~flow relation of Yehu Gorge for the next boundary condition, the mathematical model is used to calculate the several water surface lines under different flows in the excavated river reach under the recommended excavation width of 50 m and the excavation gradient for 0.05%.The results show that when the water level of Longyangxia dam is lower, the water level of Yangqu reach is similar with the natural curved line, and is hardly affected by the backwater of Longyangxia Reservoir; when the water level of Longyangxia dam is higher, the water level of Yangqu reach is similar with the horizontal line, Yangqu reach is completely submerged in Longyangxia Reservoir.The tailrace water level is dropped for 0.48 m ~ 4.47 m with the average flow of 625 m~3/s when the water level in Longyangxia Reservoir is different. The water level is dropped smaller when the river flow is becoming greater, and vice versa.(3) The one-dimensional unsteady flow equation is used to control the transient process of water pipeline and the initial boundary conditions in a hydropower station; the characteristics of the add surge chamber in tandem tube, bifurcation pipe and the units are solved by using the feature line method, the calculation results are in good agreement with the physical model test results. This model is also used in the simulation calculations for the transition process in several hydropower stations to solve problems of hydraulic engineering design. The application of the hydraulic simulation could further improve the credibility of the numerical simulation and the understanding for the physical phenomena.