Numerical Simulation Study Of Water Flow Structure Characteristics Of Open Channels Containing Rigid Vegetation

In nature,aquatic vegetation is an indispensable part of natural rivers and lakes;with the important national strategy of ecological protection and high-quality development of the Yellow River,river ecological restoration and development are constantly on the agenda,and the study of the relationship between aquatic vegetation and rivers is of non-negligible relevance to ecological restoration.In this paper,based on FLUENT software,numerical simulations are carried out to study the straight flow of the open channel with vegetation and the curved(180°)flow with or without vegetation under ten conditions with different vegetation heights(conditions B1,A,B2,B3),different vegetation diameters(conditions C1,A,C2,C3)and different inlet flow velocities(conditions D1,A,D2,D3).Firstly,we set up the same experimental study as condition A in the laboratory,and measured the longitudinal velocity at the same measurement points as the numerical simulation study using an acoustic Doppler velocimeter(ADV),and compared the data with the numerical simulation study to verify the accuracy of the mathematical model.The effect of vegetation on the flow structure of the straight channel under the change of single condition was investigated by comparing the vertical distribution of longitudinal velocity,the vertical distribution of turbulence intensity,the cloud diagram of longitudinal velocity at the same cross-section(0°,45°,90°,135°,180°)and the cloud diagram of total velocity distribution at the same cross-section(z=4cm).The main results of the study are as follows:(1)Comparing the vertical distribution of longitudinal flow velocity at the same measurement points of the test and numerical simulation A,it is found that the maximum error is 9%,and most of the errors are below 5%,and there is a good agreement between the test and simulation values,which indicates the accuracy and precision of the mathematical model used in this paper.(2)Under different working conditions,the longitudinal velocity of vegetation is less influenced in front of the vegetation zone,showing a "J" type distribution,and is more influenced by the vegetation in the vegetation zone,showing an "S" type distribution;in the vegetation layer,the longitudinal velocity first increases rapidly,and then reaches a certain height(velocity close to the initial velocity).This is consistent with the known distribution of flow velocity in the three zones;the flow velocity outside the vegetation zone is influenced by the vegetation wake and the same phenomenon of longitudinal flow velocity in the vegetation zone,but the farther the distance,the less obvious this phenomenon is;the longitudinal flow velocity will also increase with the increase of water level,the zone of rapid change of flow velocity will change with the different working conditions,and the range height will also increase with the The longitudinal velocity will gradually decrease with the flow of water.The turbulence intensity and flow velocity show approximately the same pattern,but the turbulence intensity decreases in the rapid change zone,and the turbulence intensity in the stable zone becomes less and less with the flow of water.The water level surface is affected by vegetation before it enters the vegetation zone,and the water surface slope ratio is different with different working conditions.(3)When the height(diameter)is different,the longitudinal flow velocity and turbulence intensity change rapidly with the increase of vegetation height(diameter)and lift;the turbulence intensity under the vegetation layer in the vegetation zone increases with the increase of vegetation height(diameter),and the water surface slope ratio increases with the increase of vegetation height(diameter)in front of the vegetation zone.The water surface slope ratio in the whole area also increases with the increase of vegetation height(diameter).(4)When the inlet velocity is different,the longitudinal velocity and turbulence intensity change rapidly with the increase of the inlet velocity,and the water surface slope ratio decreases in front of the vegetation area and the whole area with the increase of the inlet velocity.The longitudinal flow velocity in the vegetated area is influenced by vegetation and decreases with the increase of inlet velocity;the turbulence intensity increases with the increase of inlet velocity.(5)With or without vegetation,the water level surface of the bend is low near the convex bank and high near the concave bank;with vegetation,the water level surface is higher than that without vegetation,but its water surface cross-ratio drop is lower than that without vegetation;without vegetation,the water level surface at the bend outlet is smaller than that at the bend inlet,and with vegetation,the opposite is true.(6)With or without vegetation,the longitudinal flow velocity is larger as it is closer to the concave bank,but the flow velocity at the inlet of the bend is affected by vegetation the same as that at the straight channel;the closer the two banks are,the smaller the longitudinal flow velocity is affected by vegetation,and the concave bank is more affected by vegetation than the convex bank.When vegetation is included,the longitudinal velocity at the inlet of the bend shows a three-zone distribution in the vertical direction,while the rest of the positions are affected by vegetation,and the trend increases and then decreases with the increase of water level;the total velocity of the flow with vegetation is smaller than that of the flow without vegetation at the bend.