Study On The Flow Characteristics Of The River Channel With Submerged Congeries

Congeries are river obstacles with higher potential risks in areas where geological disasters frequently occur,especially after the Wenchuan earthquake,they are densely distributed in various basins in Sichuan.When in favorable terrain conditions,the congery is likely to lose stability during the rainstorm season and become a disaster point,and threaten the safe operation of power stations in the basin.During flood seasons with frequent heavy rains,many congeries are in a submerged state.Studying the characteristics of the water flow near the submerged congeries can enrich the research results of the flow structure near the congeries,and provide support for the optimization plan of river governance affected by the congeries during the flood season It can also lay the foundation for the subsequent start-up test of congeries.This paper focuses on numerical simulation,and verifies the numerical model with water tank experiments.It sets different flow rates,congery ratio and lateral slope of the congeries,and analyzes the time-averaged water flow characteristics,turbulence characteristics,and downstream recirculation zone characteristics near the congery.The research results are as follows:(1)Analyze the changes of the water surface profile near the submerged congery.The law of change along the way is basically the same as that of non-submerged congery,and the regulating effect of congery on water flow decreases as the submergence coefficient increases.The detention zone basically disappears,but the water blocking effect still exists,and the turbulence in the return zone will diffuse into the congery section.(2)Analyze the longitudinal velocity change near the submerged congery.The Froude number along the way in the submerged state is generally less than 1,so it is difficult to produce a water jump phenomenon.The power axis will shift to the side of the congery in the congery section,so the scouring effect is obvious.The submergence coefficient affects the flow rate change rule by changing the scope of the recirculation zone.The flow velocity is only affected by the recirculation zone above a certain flow layer,and shows a trend of first increasing and then decreasing along the water depth.The closer to the surface,the stronger the influence of the recirculation zone.(3)Analyzed the changes in water deflection near the submerged congery.The deflection mainly occurs in the congery section.The deflection direction changes at the central axis of the congery.It deflects to the right bank in the tapered section,and deflects to the left bank in the tapered section.The deflection is greater the closer to the left bank in the recirculation zone.The submergence coefficient affects the distribution of deflection along the depth of the water by changing the scope of the recirculation zone,so that the tangent of the upper and lower deflection angle of a certain flow layer alternates between positive and negative or produces a sudden change near the water surface.(4)Analyzed the turbulent kinetic energy changes near the submerged congery.The turbulent kinetic energy of the flow layer below the influence of the recirculation zone is mainly affected by the diffusion of water flow.The strong turbulence zone is located in the congery section and the downstream mainstream zone,and gradually decreases along the downstream.The turbulent kinetic energy caused by the recirculation is the largest in the flow layer above the recirculation zone.The strong turbulence zone shifts to the vicinity of the recirculation zone.The higher the flow layer,the larger the turbulent kinetic energy and its influence range.For the turbulent kinetic energy near the bottom layer,when the submergence coefficient is small,the strong turbulence zone is located near the return zone.As the submergence coefficient increases,the influence of the recirculation zone gradually decreases to disappear.At this time,the turbulence caused by the diffusion of water becomes the main factor.(5)Analyze the characteristics of the downstream recirculation zone of the submerged congery.The water flow is only affected by the backflow above a certain flow layer,and the higher the flow layer,the more obvious the backflow phenomenon.After the water flow bypasses the top of the congery,it forms a sinking water flow and produces upward buckling,which is combined with the diffused water flow to the left bank of the main flow area,and finally forms a counterflow toward the upstream at the lower boundary of the return zone.Therefore,the recirculation zone is formed by the combined influence of the high-speed water flow in the main flow zone and the sinking water flow in the recirculation zone.The larger the submergence coefficient,the closer the countercurrent position is to the congery,which will promote the upstream development of the recirculation zone.The length and width of the vortex zone will decrease,and the scope of the recirculation zone will decrease accordingly.The countercurrent flow will become weaker and eventually lead to the disappearance of the recirculation zone.The relative length and width of the vortex zone has a good positive correlation with the water blocking rate.In addition,the sinking water flow will cause the return flow to affect only above a certain flow layer,and the height of the flow layer affected by the return flow is proportional to the submergence coefficient.