Simulation Study On Open Channel Layout And Navigation Conditions Of Longxikou Hub In Minjiang River

During the construction of hydro-junction on flat terrain and wide river channel,river diversion by stages is generally adopted in the construction period,so as to ensure the realization of dry land construction requirements.When adopting the stage diversion scheme,the stream diversion work is usually undertaken by the beam narrow riverbed and the open channel.The section where the Min Jiang Long Xikou junction is located in this paper is a typical wide and shallow river channel.The junction is constructed by stage and stage diversion.During the dry construction period,the main channel on the right bank and the open channel excavated on the left bank are mainly responsible for diversion.In addition to discharging the design flood,Long Xikou junction in the dead period diversion,because the junction is located in the lower reaches of the Min Jiang river,the navigation task is heavy and the interests are involved,it also requires each discharge channel to undertake navigation tasks.Therefore,the narrow channel and the open channel in the dry period should meet the navigation requirements while completing the discharge task.In order to ensure the smooth discharge of flood water in open channel in dry period and reduce the influence of construction on daily navigation as much as possible.In this paper,by means of physical model test and numerical simulation,the water flow in the reach affected by the construction of Long Xikou junction during the dry period is studied.Each period according to the dry period the diversion and navigation flow condition of physical model test results,found that dry period using diversion discharge flow in open channel navigation,under the same flow rate,the test of navigable flow condition is significantly worse natural circumstances,and because the preliminary design of the diversion channel width is too big,cause later construction pressure,extend the time limit for a project.Therefore,in order to properly narrow the channel width,this paper uses the two-dimensional mathematical model to study the influence of the change of the channel narrowness on the water flow in the open channel section.Through the study,it is found that the variation of the width bundle narrowness of the open channel mainly has a significant influence on the water surface elevation,flow velocity and flow pattern along the test reach.Further physical model tests show that the influence of the width bundle narrowness of the open channel on the water flow conditions is consistent with the law obtained from the numerical analysis.(1)The water surface elevation along the test section.After the open channel bundle was narrow,the water level in the upstream segment obstructed high,and the water level was positively correlated with the open channel bundle narrowness.The surface of the water fluctuated in the body of the open channel.The more narrow the beam,the more violent the fluctuation of water level.After the water flows out of the channel,the water level is inversely correlated with the narrowness of the beam,and the greater the narrowness of the beam,the lower the water level.(2)The flow velocity.Because of the obstructed high water level in the upstream reach,the flow velocity tends to decrease.The peak velocity of open channel section increases with the increase of beam narrowness,and the flow velocity of its inlet section presents the flow characteristics of curved channel under the influence of river type and plane layout of open channel.The hydrodynamic axis also moves to the left bank gradually with the increase of beam narrowness.The flow velocity in the downstream section is evenly distributed and fully diffused,and the flow near the outlet of the model is reclassified into the main channel on the right bank.(3)The flow state.Before the transverse cofferdam,there are different degrees of backflow area.The backflow range and backflow strength change with the change of beam narrowness.As the beam narrowness increases,the upstream backflow range decreases and the backflow intensity weakens,while the downstream backflow area increases and the backflow intensity increases.Finally,based on the measured results of navigable flow conditions and ship model test results in each working condition of the test section,combined with the influence law of open channel bundle narrowness on the water flow,it was analyzed that the plan of moving 4 holes to the left of the guide wall on the right bank could not only relieve the construction pressure in the later stage,but also basically meet the navigation requirements in the test section.The reasonable width of open channel is 234 m.In order to further improve the navigable flow conditions in the open channel section,the plane layout of the channel can be optimized by changing the length of the vertical cofferdam on the left and right Banks,and the bending radius of the flow boundary is gradually increased.The results show that the increase of the bending radius of the boundary of the diversion channel can effectively reduce the size of the cross-flow at the entrance of the channel and improve the navigable flow conditions in the channel.Through further comparison and selection analysis,the width of the diversion channel in the construction period of Long Xikou junction is 234 m,and the optimal conditions of flood discharge and navigation are obtained when the cofferdam is arranged according to the sixth working condition.