| The rear of the pier on the WES (Water-ways Experiment Station) spillway is expanded to form flaring gate pier (FGP), which is combined with stepped spillway in the downstream. The united dissipation system composed of FGP, stepped spillway and stilling pool possesses advantages of both FGP and stepped spillway. In case of low flow rate, the energy of flows is dissipated by eddies on the steps. Whereas, in the case of large flow rate, the outflows are accelerating in straight lines from gate chamber and form two thin and high nappes, which have multiple hydro-pneumatic interfaces. They contact with air in big range and collide mutually across the downstream steppes, then drop into the stilling pool. It makes the aerification considerable and dissipates partial energy of flows. And the flow discharge per unit width is increased several times than the single stepped spillway. Therefore, the flows behave obviously three-dimensional characteristics. Based on the previous studies and combined the experiments with numerical simulation, the flow hydraulic characteristics and several problems of the united system were studied in this paper. The accomplishment of this study will be of theoretical and practical significance. The main contents of the studies and achievements are as followed: 1. The three-dimensional numerical simulations of turbulent flow on the united dissipation system composed of FGP, stepped spillway and stilling pool have not been reported yet. In this paper, the three-dimensional turbulent flow on it was simulated successfully first time. The simulating results of the water wings, the free jet, the aerated cavity and the eddies were plotted. The meshing methods with appropriate quality and scale were studied. The principles and notes of meshing the simulating domain were offered. 2. The study is combined with Suofengying hydropower station, in which the X-shape FGP is used at first time. By the body types comparison of X-shape and Y-II-shape FGP, it indicated that in case of low flow rate, the energy of flows is dissipated by eddies on the steps, whereas in the case of large flow rate, the outflows are accelerating in straight lines from gate chamber and it makes the aerification considerable and dissipates partial energy of flows. 3. It indicates that on the juncture of the spillway surface and the first step there exists negative pressure, which has not been measured in previous experiments. Based on the position of the negative pressure obtained from calculation, the experimental results validate the existence of the negative pressure. The preliminary discussion on cavitation erosion was carried out. It indicated that the cavitation phenomena may occur at the juncture of the spillway surface and the first step. However, owning to the considerable aerification and eddies, the cavitation erosion will not occur. 4. The flow characteristics of X-shape FGP, stepped spillway and stilling pool in the cases of difficult discharge per unit were compared and analyzed. The velocity field of the united system was divided into several domains to describe. The flows of the FGP downstream form four regions: the main velocity region, the eddies region in the steps, the cushion region, and the aeration region. The three corresponding velocity regions in the stilling pool are the underflow region, the low velocity region and the surface current region. 5. From the view of the hydraulic characteristics and combined the practical applications with formula derivation, the estimated formula of the nappes' distance was obtained. The influences of the WES' slope angle and the sill's height on the nappes' distance and the ratio of energy dissipation were analyzed. Moreover, the estimated formulas of the collided point's position of the two nappes and its dissipating ratio were derived. Then, the influence of FGP convergence angle on these parameters was analyzed.6. The different energy dissipating characters of each part of the nappes were analyzed and the formulas on their dissipating ratio were provided. In addition, the dissipating efficiencies of X-shape FGP, Y-II-shape FGP and no FGP were compared. Due to the new theme that the FGP is set on the upstream of stepped spillway, the study on its dissipating mechanism is not abundant. The divided velocity field of the united system has certain referent significance. The problem of negative pressure on the steps has universality and it can be researched further combined with practical projects into the problems of FGP convergence angle, WES' slope angle, sill's height and dissipating efficiency.
|
PDF Full Text Request