Experimental Study On Turbulence Characteristics Of Circling Flow Around A Cylinder Pier

Flow around a cylinder is a classical fluid mechanics. It is widely found in engineering, construction, overhead lines, offshore drilling and other areas of scientific research and engineering practice. For example, bridge pier local scour and protection pier cofferdam excavation pit in bridge Engineering. To solve these problems better , we must have detailed knowledge on the local hydraulic cylinder flow around bridge piers.For a long time,Many domestic and foreign scholars and scientists conducted a large number of studies of model experiment and numerical simulation and achieved some achievements to flow around cylindrical bridge piers. But so far, flow patterns and local hydraulic characteristics study around the cylinder pier are very limitied ,just because flow and sediment movement near the piers is very complex and has numerous influencing factors. Existing data can not be satisfactorily discussed to flow and scour around cylindrical bridge piers, so still need to continue research in this area.In this thesis, We studied turbulence characteristics of circular cylinder piers which diameters are 0.05m,0.10m,0.15 and 0.2m under different flow conditions by model experiment. Three-dimensional ultrasonic speedometer Vectrino was used to measure velocities on three points of nine vertical of seven cross-sections. Using statistical theory and turbulence mechanics knowledge, We calculated turbulence velocity, turbulent intensities, time averaging velocities, reynolds stress along the flow direction and cross-section,。Simultaneity, I analyzed their distribution regularity. The maximum depth of local scour is measured. And the relationship of the cylinder pier diameter, the discharge and the maximum depth of local scour is analyzed.Velocity datas indicates that the velocity pulsing process of all the measuring points around cylinder is almost similar. Probability distribution of longitudinal , horizontal and vertical turbulence velocity obeys the law of normal distribution. We compared the experiences probability curve from the measured data with the theoretical normal calculation probability curve and concluded that curve is closer on the left and right of cylinder than in the before and after of cylinder in the same depth, curve is closer in the free zones than in the shear cutting zone near the wall. In addition, this paper calculated and analyzed distribution of the tuebulence intensity, the time average velocity and the reynolds stress along the flow direction and cross-section in the different conditions which is the same flux or diameter. Finally, by analyzing the measured local maximum scour depth data ,we obtained the distribution of the maximum depth of local scour in the same flux which is parabolic trend by analysing and comparing the maximum depth data of local scour maximum and cylinder diameter.