Study On Navigable Flow Condition Of Narrow Deep Sharp Bend Channel

The flow pattern of curved channel is complex and the velocity distribution is uneven.It is difficult for ships to operate in the curved channel,and it is easy to cause water traffic accidents.Therefore,it is very important to study the navigable flow condition of curved channel,especially narrow deep sharp bend channel.Natural rivers are basically curved due to the influence of geology,rainfall and gravity.Under the combined action of gravity and centrifugal force,the flow structure in the bend redistributes along the longitudinal and transverse direction,which makes the flow pattern very complex and seriously affects the safety of ship navigation.Moreover,the flow characteristics of the bend are greatly affected by the geometric structure of the bend.The changes of the width depth ratio,bending radius and bending degree of the bend will cause the changes of the water surface shape,velocity distribution and transverse circulation in the bend.Based on the overall experimental study of Shanxiu shiplock project,combining the results of physical model test with numerical simulation analysis,this paper analyzes the navigable flow conditions of the sharp bend channel upstream of the dam site of Shanxiu Hydropower Station,and adopts RNG The K-ε model is used to simulate the change law of bend flow under different bend radius and bend degree,which is of great significance for further understanding the change law of bend flow structure and taking reasonable ways to improve the bend flow conditions.(1)Xkvms-03 large-scale surface flow meter was used to measure and collect the surface velocity of the model sharp bend reach,and the variation law of water level and velocity in the natural narrow deep sharp bend reach was analyzed.The results show that the maximum transverse gradient of the bend is near the top of the bend;when the water flows into the bend,the main flow moves to the original side,and then to the concave side after passing through the top of the bend,and the maximum velocity is near the convex side of the bend;with the increase of the flow,the more the main flow moves to the convex side,the worse the flow condition is.(2)The three-dimensional numerical simulation of the sharp bend section in the upstream of Shanxiu model is carried out to further analyze the flow characteristics of the natural sharp bend channel.At the same time,the physical model test data are used to verify the logarithmic model.The results show that the calculated values of the mathematical model are basically consistent with the measured values,which can be used for the research of the bend flow.The numerical simulation results show that the flow velocity in the bend changes along the vertical line and presents a certain rule,and the circulation structure and intensity change along the bend.(3)The RNG K-ε model is used to simulate the change of flow structure in the bend with different bend radius.The results show that the change of bend radius has influence on the transverse gradient,velocity distribution,transverse circulation and turbulent kinetic energy.The smaller the bending radius is,the more concentrated the main flow is and the greater the velocity difference between the concave and convex bank is.(4)The RNG K-ε model is used to simulate the bends with 60 °,90 °,120 °,150 °and 180 ° curvature under the same bending radius.The simulation results show that besides the bending radius,the change of the curvature also causes the change of the flow characteristics in the above bends,and the specific change rules are as follows: the transverse gradient,the main stream position,the circulation structure and the intensity of the bend.