Simulation Study On Local Scour Downstream Of Dangka Hydropower Station

The local scouring problem downstream of the discharge structure is a key issue for the safe and stable operation of water conservancy and hydropower projects.To investigate the shape and depth of the scouring hole under the erosion equilibrium state of the downstream of the discharge structure,this paper takes Dangka Hydropower Station as the research object,and takes 16 sets of experimental data of the model test as the verification data of numerical simulation.Based on FLOW-3D,4 kinds of grid calculation results were carried out for the sensitivity analysis,and the three-dimensional numerical simulation of the downstream scouring process of hydropower station under different flow rates and different median diameters was carried out.The simulation results of three bed load sediment transport rate formulas(Meyer-Peter,Nielsen,Vanrijn)were analyzed and compared.The paper concludes as follows:(1)Under different flow conditions,the relative errors of the flow rates obtained by the 4kinds of mesh simulations are small.At higher flow rates,the simulated average inlet velocity and scouring depth are in good agreement with the experimental data and at lower flow rates,the simulation results have larger errors.(2)The scouring process can be divided into the following three stages.In the initial scouring stage,the flow rate was large and the scouring intensity was high.In the second scour phase,the scour depth and range increased rapidly.In the third stage of scouring,the morphology of the scouring hole changed slightly and was close to equilibrium.Within 40%of the period of scouring,the depth of the scoring hole can reach 80%of the scouring balance depth.(3)Under the condition that the median diameter of the sediment is 50mm and the flow rate is 345.36 m~3/s,the relative errors of the simulated scoring depth and length with the experiment are 0.87%and 1.5%,respectively.Under the conditions of median particle size of50,100,300 mm and flow rate of 345.36 m~3/s and 400.48 m~3/s,the relative error of the maximum erosion depth obtained by simulation is below 20%.(4)The simulation results of different sediment transport rate formulas under the same flow conditions show that the shape of the scouring hole in each working condition is irregular ellipse,and the deepest point is located in the center of the scouring hole.Among them,the simulation results of the Vanrijn formula cannot predict the shape of the scouring hole well.The simulation results of the Meyer-Peter formula are in good agreement with the model test results,and the errors are within 20%.The simulation results based on the Nielsen formula only agree best with the test results when the median particle size is 50 mm.The larger the particle size of the sediment,the worse the simulation results match the test results.