Preliminary Dicussion On The Mechanism Of Underwater Root Stones Scouring In The Yellow River Dam Buttress Engineering

The dam buttress engineering is an important part of the Yellow River regulation project.The stability of the dam buttress engineering will directly affect the safety of the Yellow River embankment.The dam buttress engineering generally uses the scattered root stones.Therefore,it is of great significance to study the mechanism of the underwater root stones scouring for the design of the dam buttress and the prevention of accidents in the dam buttress engineering.The flume experimental was carried out to test the force of a single underwater root stone,and the FLOW-3D computational fluid dynamics software was used to simulate the experiment.The differences between the experimental results and numerical results were compared and analyzed.The results showed that the flow velocity and drag force coefficient obtained by the numerical model were in good agreement with the experiment results.During the experiment,by changing the flow velocity and the shape and size of the block,the force of the root stone was tested,and the horizontal drag force and the horizontal drag force coefficient of the root stone under the action of the water flow were obtained.Compared with the rectangular root tsones,the drag force coefficient of the sphere was more stable with a variation range of 0.4~0.5.For the rectangular root stones,the drag force coefficient of the block was greatly affected by the block Reynolds number and the block size.The drag force coefficient usually increased with the increase of the block Reynolds number,lengthto-height ratio and width-to-height ratio of the block.The drag force coefficient finally tended to be stable,and the stable value was between 0.8~1.1.According to the ratio of 1:100 of the actual dam buttress engineering,the physical model and the FLOW-3D numerical model were established.The differences between the physical experimen and numerical simulations were compared and analyzed.The numerical simulation was accurate in the flow field and the force of the root stone.Based on the analysis of the variation of the flow field of the dam buttress engineering under different flow rates,the maximum flow velocity appeared in the river area,which is 2.0 m away from the right bank.The upper cross angle and the dam head were the most dangerous areas where the velocity is greater than that in other areas around the dam buttress.Based on the analysis of the turbulent kinetic energy,it was found that the turbulent kinetic energy in the upper cross angle was the biggest.So the upper cross angle was the most dangerous area and needed more attention.The drag force coefficient under different flow velocity was calculated.The drag force coefficient of the physical model was 0.84,and the drag force coefficient of the numerical simulation was 0.86.The two values were close to each other.Therefore,in the early analysis process,the numerical model experiment could be used to calculate the flow field of the river and the flow force in different areas.And then it could be preliminarily judged whether the underwater root stones would be scoured and lost.