Study On The Hydraulic Characteristics Of Uniform Flow In Circular Pipe

Due to the excellent hydraulic performance and structure property,pipes with circular cross-section are widely applied in practical engineering,such as urban drainage pipelines,non-pressure tunnels etc.The flow in circular pipes is often run partially-filled in consideration of some safety factors,and adaption of variation of discharges in different period preferably.The partially-filled flow in circular pipes is a kind of open channel flows with free water surface.Many researches have conducted study on open channel flows since 1950 s,while most of them concentrates on only the channels with rectangular cross-section or trapezoidal cross-section.There are very few studies of circular open channel so far,both at home and aboard.The special shape of cross-section with curves makes the hydraulic performance,including velocity distribution,much more complicated and changeable,which are complete different from that of open channel flows with other cross shape.Besides,the turbulent characteristics and velocity distribution are also totally different from pressured pipe flows,since the flow in the pipes is driven by gravity,not by pressure of the wall.To conclude,the hydraulic characteristics of flow in circular-shape open channel with water surface are extremely complicated and there is no good description of this phenomenon at present.Based on the theory of computational fluid dynamics and the findings at present,this thesis presents study results on the hydraulic characteristics of uniform flow in circular pipe.The main factors making the unique hydraulic characteristics of circular open flows includes the diameter of the cross section,the roughness of the wall,hydraulic slope,and depth ratio.The FLUENT software is used to numerically solve the three-dimensional numerical models.To improve the computational efficiency,the free water surface of the flow is treated as a plane cover with no wave.The presented models have been verified with measurement,and there is little difference with measured results.The study also indicates the existence of secondary currents,which fits well with the physical truth.According to the results,the position of maximum velocity is located below thefree water surface due to the secondary currents and the contractive shape of the wall,and the position varies with the depth ratio of the flow in the pipe,the roughness of the wall as well.The velocity distribution can be divided as two different section vertically,with y/h<0.2 defining the inner region or wall region,and y/h>0.2 defining the outer layer.The mean velocity profile accords with the log-low formula in the wall region,and that in the outer region accords with the parabolic function.Along the width direction,the mean velocity profile accords with exponential formula.Coefficients in these formulas have been gained through the analysis to the data from calculation.Furthermore,the unique non-singleness varying pattern between the discharge and the depth in the pipe flow,the distribution law of the boundary shear stress and also the friction coefficients are also fully analyzed.The corresponding relation of the maximum velocity in the free water surface and the mean velocity was derived as well.The results shows that the ratio of the maximum velocity in the free water surface and the mean velocity can be influenced only by the roughness of the wall and the depth in the pipe.The friction coefficients also vary with the depth.The presented studies give a relatively comprehensive description to the hydraulic characteristics of the circular pipe running partially full with a steady uniform flow.These results can provide some scientific basis to propose a new non-contact measurement of the discharge in circular pipes.And it can also give a significant guidance to the uniform flow in the open channel with arbitrary shape.