Numerical Simulation Of Hydraulic Characteristics On Stilling Basin With Contraction Pier And Drop Sill

Abstract:In hydraulic engineering,oscillating water jump caused by low Froude number has always been a problem which is difficult to solve.In this paper,due to objective conditions that stilling basin scale can not be changed to eliminate the oscillating hydraulic jump problem caused by large discharge per unit and low Froude number,setting the contraction pier at the end of the diffusion section worked out to solve this problem.Using experimental and numerical simulation methods to study the changes of flow pattern and hydraulic characteristics in this compound stilling pool under different downstream water levels and analyze the causes and avoiding condition of oscillation flow and the energy dissipation,main conclusions were drawn as follows:(1)The large scale and unstable vortexes at the shear plane of the main flow and the flow in the pool,compared to the solid walls,water cushion formed because of the drop sill,which made it harder to suppress,were the reason for oscillation of the pool with drop sill.The oscillation also caused large wave of the water of the pool.Without changing overall geometry and relying on local shape optimization or adding other auxiliary energy dissipater couldn’t eliminate oscillatory flow pattern of the stilling basin with drop sill through the experiments.(2)The contraction pier changed the conditions of main flow.The drowned jet flow started to mix with the flow in the pool to form horizontal and vertical diffusion,which damaged the unstable large-scale vortexes and formed new and stable three-axis vortexes.The oscillatory flow pattern finally was eliminated.(3)There were three typical steady-state flow when downstream water level changed from high to low,submerged jets and submerged bottom flow,submerged jets and slightly submerged bottom flow and free jet flow.The energy dissipation rates were 55.5%,60.5%,62.0%as downstream water level were 2398.54m,2394.86m,2392.54m,which was higher than the same condition of pool with drop sill.It indicated that the stilling basin with contraction pier drop sill could not only eliminate the oscillating flow problem caused by large discharge per unit,low Froude number,but also adapt to a substantial change in the downstream water level when there was not tail or low tail.(4)With respect to the stilling basin with drop sill,the contraction pier and drop sill compound pool had more intense turbulence flow and high energy dissipation rate.The turbulence energy and energy dissipation rate of the x=70m cross section were 6.75m/s2 and 41.6m2/s3,which were higher than the pool without contraction pier.The pressure and velocity distribution of the stilling basin were three-division.The pressure in the front of the pool gradually reduced,then became close;the velocity of the main flow was close,while the velocity of reflux flow gradually increased,along with the energy dissipation rate,which showed more intense turbulence and mix between the main flow and the flow of stilling pool.