| Our country has a vast territory and has suffered a lot of geological disasters,especially in some mountains and canyons.Because of the natural geological disasters such as earthquake,landslide and debris flow,it is easy for the natural river to appear obstacles composed of soil and gravel,which will block the river and hinder the normal flow of water.These obstacles are generally fixed on the bank wall.Under normal flow conditions,the water can not transport them to the downstream,so they are called accumulation bodies.The existence of the accumulation body in the river course will occupy the original river course space,form the squeezing effect on the water flow,and change the hydraulic characteristics of the river flow.At present,flume test,cylinder flow test and corresponding numerical simulation are the main ways to study the change rule of flow structure.The influence of accumulation body on river flow in this paper has many similarities with that of cylinder flow,and we can draw experience from previous research results.Based on the previous flume test,this paper adopts the method of flume model test and numerical simulation to simulate and analyze the four variable factors of inlet flow,deposit width,bottom slope and bottom roughness.In this paper,an equal scale model is established by using ANSYS software.When the model is meshed,unstructured tetrahedral mesh is used.The standard k-?turbulence model is selected to import into fluent for simulation calculation,and VOF is selected to track the change of free water surface.The main research results are as follows:(1)The variation of water surface profile under different simulated test conditions is analyzed.From the overall change law,there will be some backwater in the upper reaches of the river,but the flow is relatively smooth as a whole,the water surface line along the course has almost no change,and the vertical and horizontal gradient are almost 0.In terms of backwater effect,the flow rate,the deposit advance width and the bottom slope have a positive impact on the backwater height.The deposit advance width has the largest impact on the upstream backwater height,followed by the bottom slope and flow rate,and the change of roughness has little impact on the upstream backwater height.When the water flows through the deposit and gradually flows to the downstream,the water surface line will drop,and the longitudinal and transverse ratio drop of the water surface will be along The process will gradually increase,and the most obvious change is the test condition of 0.9b Deposit Advance width.Under this test condition,the influence range of water surface profile is the widest,and the change range of longitudinal gradient and transverse gradient is also the largest.After bypassing the deposit,the water flow will flow to the downstream,and at the same time,it will spread to the left bank,at this time,there will be water jump phenomenon,the water surface profile will rise along the process,and the longitudinal gradient and transverse ratio of water surface The descent will gradually return to 0.Because the water flow in the steep slope test group is always in the state of rapidity,the water surface will continue to decline along the course,and there will be no hydraulic jump,which is different from other test conditions.At about X*=2.5,the water surface began to be stable,and the vertical and horizontal gradient of the water surface also tended to 0,and the overall flow was in a stable state.For the longitudinal gradient of water surface,the influence effects of each variable from large to small are as follows:bottom slope,advance width and flow;for the horizontal gradient of water surface,the influence effects of each variable from large to small are as follows:advance width,bottom slope and flow.The change of roughness has no obvious effect on water surface profile and water surface gradient.(2)The variation of time averaged flow field under different simulated test conditions is analyzed.In the upstream backwater area,because the overall flow is relatively smooth,there is almost no change in the longitudinal velocity and cross-section specific energy of each section,and the flow has no deflection;from the gradual expansion section of the accumulation body,the flow is affected by the accumulation body,the longitudinal velocity and cross-section specific energy start to increase,and the water flow direction to the right bank deflects obviously.Near the central axis of the accumulation body(x*=0),the longitudinal velocity and the The specific energy of the cross section reaches the peak value,and the deflection amplitude of the water flow to the right bank reaches the maximum.After the water flow passes through the central axis of the accumulation body(x*=0),the advance width of the accumulation body decreases,and the water flow will gradually spread to the left bank to recover to the natural flow state,and the longitudinal velocity and the specific energy of the cross section will gradually decrease along the process until it is stable.At this time,the flow deflection changes more complex:the flow in the flow test group is inclined to the left bank at the downstream,and the deflection amplitude decreases along the way to tend to 0;the test group with the deposit advance width of 0.9b,because of the large size of the deposit,the range of influence on the flow is also increased,and the flow deflection appears back and forth at the downstream;the test group with steep slope,because there is no water jump phenomenon,water There is still a lot of kinetic energy in the flow,and because of the large bottom slope,part of the potential energy will continue to convert into kinetic energy in the process of flow to the downstream,and the longitudinal velocity will continue to increase along the way,and because of the large kinetic energy of the flow,the flow deflection in the downstream presents the phenomenon of left and right fluctuations.(3)The change of turbulent kinetic energy under different simulated test conditions is analyzed.On the whole,the turbulence in the upstream is weak and the turbulent kinetic energy is small.In the area(x~*=-1?1)affected by the accumulation,because of the influence of accumulation,the flow velocity increases,so the turbulent kinetic energy is obviously strengthened in this area.In the region of x~*=0?1,it is the strong turbulent region of the flow,and the turbulent kinetic energy gradually increases along the path until it reaches the maximum value.In the X~*=2?6.5 area downstream of the accumulation body,due to the energy dissipation effect of the hydraulic jump,the flow velocity decreases,and the flow will gradually return to the natural state in the process of flowing downstream.There is a small area of low turbulent kinetic energy on the right side of the accumulation body,which is the corresponding return area.The flow velocity in the return area is low,so the turbulent kinetic energy is small.The area of strong turbulent kinetic energy in the downstream is the largest in the test group of accumulation and occupation of wide body,which has the largest impact on the turbulent kinetic energy.The roughness test group has the smallest impact on the turbulent kinetic energy.The change of roughness has no obvious impact on the turbulent kinetic energy.(4)The change of reflux zone under different simulated test conditions was analyzed.In this paper,by finding out the coordinates of u=0 and v=0 points of each test group,the boundary line is a curved curve.At the same time,the curve in the form of y=AX~B+C is used to fit,and the circumfluence boundary is obtained.Through the analysis and research,the influence of the deposit width on the scope of the return area is the largest,followed by the bottom slope,the flow rate is the second,and the influence of roughness on the scope of the return area is almost 0;for the relative strength of the circulation,its change is basically consistent with the law of the flow deflection change,which will not be discussed here;under certain conditions,when the flow bypasses some objects,a fixed vortex structure will be formed According to the previous formula,when the flow rate is small,the corresponding flow rate is also small,and a fixed and stable vortex will be formed in the reflux area.When the flow rate increases gradually,the Reynolds number Re of the flow will also increase,and the vortex will gradually fall off from the outer edge until it disappears.If the flow rate continues to increase,the Reynolds number is greater than 12000,a new vortex structure will appear in the downstream of the original vortex. |
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