Experimental Study On The Disturbance Of Propeller Wake To Sediment Under Hydrostatic Condition

The water environment problem has got more and more people's attention.In recent years,with the development of the Xiangjiang River water environment treatment,people noticed that the wake in the ship's navigation has a certain disturbance effect on the sediment.On the one hand,when the vessel starts and leaves the terminal,the propeller wake will produce scouring damage to the riprap bed,affecting the stability of the quay structure;on the one hand,the ship's wake disturbs the water body and causes the start-up resuspension of the sediment on the bed surface and the release of pollutants from the sediment when the vessel is sailing.Therefore,in order to explore the scour conditions of the propeller,and to provide basic data for further analysis of the sediment resuspension on the water environment,it is necessary to carry out experimental research on propeller wake disturbance to the sediment.The three-dimensional point velocity meter(NDV)is used to measure the near-bottom velocity distribution and bed scour of the propeller wake in hydrostatic condition.The analysis of the bottom flow velocity distribution and the extent and depth of the bed surface erosion when the propeller rotates at different speeds,different paddle diameters and different heights from the bed surface.That mainly led to the following conclusions:1.From the analysis of the physical model test data,it can be seen that propeller rotation speed,propeller diameter and distance from the bed surface will all affect the size and distribution of the near-end flow velocity and the extent and depth of the bed surface erosion2.The size and distribution of propeller wake near-bottom velocity are related to propeller diameter,rotation speed and distance from the bed surface.The larger the propeller diameter,the faster the speed,the smaller the distance from the bed surface,the greater the near-bottom velocity of the bed surface,and the empirical formula of the maximum near-bottom velocity distance from the propeller plane position.The near-bottom flow velocity on the cross-section is symmetrically distributed about the propeller axis,showing different regularity when the propeller is at different heights from the bed surface3.According to the changes of propeller wake flow to the bed's scour area and depth,the scour process can be divided into three stages:initial stage,development stage,and stable stage.The development of its axial length,transverse width and maximum scour depth accounted for 80%,15%and 5%of the entire flushing process,respectively.4.The extent of propeller wake flow over the bed surface and the maximum scour depth change,along with the increase of propeller diameter,rotation speed and height of the bed surface,the axial length and transverse width of the scour hole increase;the height of the propeller increases with the bed distance,its maximum scour depth decreases.And analyze the distance from the position of the maximum scouring depth to the paddle surface.