Experimental Study On Flow Field And Scouring Characteristics Around River Pipeline

With the development of the transportation industry,the pipeline transportation has brought great convenience to people's life in the aspects of transmission,gas,oil and power supply.However,the problem of underwater pipeline destruction in recent years has not been solved very well.Once the pipeline was damaged,it will not only cause economic loss,but also bring inconvenience to people's lives and cause a series of environmental pollution problems.There are not many researches on pipeline scouring at home and abroad at present,and the research results can be applied to practice more rare.So it is urgent to speed up the research on the flushing of the pipeline.The purpose of this study is to comprehend the characteristics of the flow field around the pipeline and the characteristics of scouring through the physical model test.It will provide the scientific basis for the pipeline engineering design.The study can also enrich the pipeline and river erosion mechanism,and to promote the further development of the theory of sediment movement at the same time,.In this study,ADV was used to measure the three-dimensional velocity around the pipeline by the method of fixed-bed model test and movable-bed model test to study the flow field and scouring law around the pipeline model.In this experiment,a total of 12 working conditions was set,which moving bed model test and fixed bed model test of the six groups.Through the comparative analysis of the fixed-bed model test and the movable-bed model test results,the following rules can be summarized:(1)The whirlpool width of the transverse tube is kept within the range of 1.2 and 1.5 times in different working conditions and the vortex is continuously formed and disappears in the process of large whirlpool.The swirl was narrowed by Froude number,and when Froude number of riser was between 0.104 and 0.393,the trailing vortex width was between 1.2 and 2.0 diameters(2)The vertical flow velocity decreases and the vertical velocity increases,and the maximum flow rate of the horizontal pipe is at the plane of the horizontal axis of the transverse pipe,and the maximum flow rate of the riser appears on both sides of the pipe.The turbulence intensity and Reynolds stress increase with the increase of flow velocity,and the distribution of bottom,middle layer,surface velocity,turbulence intensity and Reynolds stress of the riser are basically the same,and the horizontal pipe axis The turbulence intensity and Reynolds stress are the largest,and the flow rate is the biggest.(3)It can be seen the net horizontal thrust growth of the fastest,and the slowest buoyancy growth from the horizontal thrust,dynamic buoyancy and net horizontal thrust with the flow rate of the curve.(4)When the flow rate before the pipe is less than the velocity of the model sand,the pipeline will not produce local scour.When the flow velocity is larger than the velocity of the model sand,the position of the transverse pipe scour is about half pipe diameter,and the position of the horizontal pipe is on both sides.(5)The horizontal flap depth of the transverse tube is greater than the riser in the same flow conditions,which is due to the turbulence around the transverse tube is greater than the riser.When the cross tube is half buried in the model sand,the greater the flow rate,the shorter the pipe from half to full.The flushing speed of the riser process is relatively fast,and the maximum scour depth is reached when the local flushing is stopped.(6)From the shape of the scouring pit,the range of the scouring pit around the riser increases with the increase of the flow velocity.While the horizontal pipe scouring pit is basically the same,and the width is about three times in the direction of the flowing water.