| The maximum dam height of Liyuan Hydropower Station Project is 155m,and the maximum single discharge is 210.9m~2/s,belong to a typical flood discharge project with high head and single flow width.In order to prevent the flooding and fog rain from affecting the operation of the ground powerhouse and the stability of the downstream Guanyinyan accumulation body,a new type of underflow energy dissipater is adopted a sudden expansion type stilling basin for the outlet.The existence of bottom drop and sudden expansion can reduce the bottom velocity on the stilling basin and increase the energy dissipation rate effectively,but it also causes the complicated hydraulic characteristics in the stilling basin,especially the distribution characteristics of the fluctuating pressure on the stilling basin slab will seriously affect the safety and stability on the stilling basin slab.The experimental test and numerical simulation were conducted to study the hydraulic characteristics of the sudden expansion of the stilling basin systematically,and the appropriate inlet type of the stilling basin was selected.The main research results are as follows:(1)Through the hydrodynamic test of Liyuan Hydropower Station,it is found that the flow pattern in the original scheme of the stilling basin is a mixture of submerged jet and hydraulic jump;In the middle part of the stilling basin,when the main stream of the submerged bottom enters,the maximum bottom velocity is about 20m/s,which is not easy to cause abrasion damage to the stilling basin slab.The maximum value of root mean square(RMS)of fluctuating pressure appears in the vicinity of the front of the stilling basin and the extension line of the side wall under various working conditions,so protection should be strengthened.(2)Against the original plan,the fluctuating pressure on the stilling basin slab is generally larger than the safety threshold of problems.The model test results show that the method of amending the sudden enlargement to divergent cannot significantly improve or solve the problem of fluctuating pressure on the stilling basin slab completely;Adjusting the original-10°cantilever to-8°incident angle can reduce the fluctuating pressure on the stilling basin slab effectively.Under the design conditions,the RMS of the fluctuating pressure is less than 5m head,which meets the requirements of the design flood level and the operating conditions below.In addition,the fluctuating pressure is low-frequency vibration,which is not easy to cause resonance damage to to stilling basin slab,and it can be used as the prioritization scheme.(3)In order to further analyze the flow structure in the stilling basin,based on Flow-3D software,large eddy model and tru VOF method were used to simulate the time-average pressure,root mean square(RMS)of fluctuating pressure,probability density distribution and power spectral density on stilling basin slab.Through comparison with physical model results,the simulation results show that the LES model can simulate the water flow fluctuating pressure in stilling basin reliably.The fluctuating pressure in the water jump area of the sudden expansion in the stilling basin is mainly affected by the low-frequency large-scale vortex.From both quantitative and qualitative perspectives,the horizontal and vertical distribution laws of the time-average pressure and the RMS of the fluctuating pressure on the stilling basin slab were explored,and the internal relations between the fluctuating pressure distribution and the velocity and vorticity were obtained by combining the characteristics of the vortex.(4)Based on the numerical simulation,the hydraulic characteristics distribution on the stilling basin slab under different sketch parameters,such as different incident angles(the original scheme and the recommended scheme),different expansion ratio,drop and traditional bottom flow,was analyzed comprehensively.The recommended sketch shape of the stilling basin was finally determined by comprehensive comparison and selection. |
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