Numerical Simulation Of The Scour Characteristics Of Amixed-flow Nozzle Under Water

Jet scour is an essential link in dredging engineering,water conservancy development and ocean engineering.The progress of water jet technology directly affects the development and utilization of rivers,reservoirs and ocean resources.It is of great value in engineering application to study the scour characteristics of mixed flow nozzles and systematically analyze the influence of various parameters on the scour results.Based on fluid FLOW-3D simulation software to establish the mixed nozzle and round nozzle jet scouring numerical model,the control variable method is used to design a variety of submerged jet flushing conditions,from scour velocity distribution,features and characteristics of suspended sediment,etc,analysis the simulation results,the initial jet velocity,jet standoff distance and the sand bed particle size on the result of erosion,The scouring effect of mixed flow nozzle jet and circular nozzle jet is compared.The main conclusions are described below:(1)The flow velocity distribution,the size of the scour pit and the range of suspended sand of the mixed flow nozzle are better than that of the circular nozzle.Compared with the scour process of the circular nozzle,the flow velocity improvement effect of the mixed flow nozzle scour is between 12%and 18%,and the maximum depth improvement effect is between 0.3%and 16.5%.(2)The larger the initial jet flow velocity is,the larger the size of scour pit and the area of suspended sand will be,and the maximum impact depth has a positive linear correlation with the initial jet flow velocity.In the strong scouring condition with large initial flow velocity,the influence of initial flow velocity on pit radius and maximum suspended sand width is strong,but the influence on dune height and maximum suspended sand height is weak.The sensitivity of the maximum depth to the initial flow velocity of the mixed flow nozzle is smaller than that of the circular nozzle.(3)There is a critical target distance to optimize the effluent scouring effect,and the critical target distance appears between 200mm and 250mm.Compared with the circular nozzle,the mixed-flow nozzle increases the peak value of the maximum impact depth and slows down the trend of the maximum impact depth decreasing with the increase of target distance.(4)When the initial flow velocity and jet target distance are the same,the larger the particle size of bed sand is,the smaller the size of scour pit and the range of suspended sand is.The maximum scour depth,scour pit radius and maximum suspended sand width are all negatively correlated with the sand bed particle size in the scour process.In the scour equilibrium state,the accumulation height of the dune at the edge of the scour pit first increases and then decreases with the increase of the sand bed particle size,and the maximum suspended sand height is negatively correlated with the sand bed particle size.