The Numerical Simulation Study Of The Submerged Dikes' Inference On River Channel Roughness

Computational Fluid Dynamics (short title CFD) is a new independent subject that is based on the classical hydromechanics and numerical calculation method. Through the method of computer numerical calculation and image display, it describes the flow field numerical solution quantitatively in time and space, so as to achieve the goal of the research of physical problems. It overcomes the weakness that the theoretical analysis method cannot give the analytical results for most nonlinear situation and the test methods are affected by measuring precision, funds, manpower and material resources of the huge cost and long circle. It has the double characteristics of theory and practice, and is applied in water conservancy,shipping,Marine,environment and other fluid engineering field successfully.River channel roughness often is used in hydraulic calculation such as floods evolution calculation, river channel regulation and so on. It is mainly used to inquire the water surface line. River channel roughness is very sensitivity to water surface line.Its precision has a great influence on calculation accuracy. In the floods evolution calculation, river channel roughness is closely related to the calculation of design flood level; in river channel regulation,river channel roughness affects the excavation and backfilling calculation in cubic meter of earth and stone. Only select appropriate river channel roughness can formulate reasonable, economical project scale.This text using CFD software Fluent, coupling VOF method of two phase flow and k-εturbulence model, making the numerical simulation for river flow field with the submerged dikes, is aimed at exploring the submerged dikes' influencing mechanism to river channel roughness, in order to make the result of physical model test further perfection.This paper studies the content for the project which selectes from follow-up research of the school project "the experimental study of the submerged dikes'inference on river channel roughness";With regard to those flow fields of river channels with 50cm,25cm,12.5cm,6.25cm spacing'dikes and original river channel corresponding to flow 4m3/h,8m3/h,15m3/h,25m3/h,75m3/h, total of 30 kinds of working conditions, the author conduct numerical simulation research, analyze variation of roughness of river channel of building submerged dikes, receive the influence law of the ratio between the water depth and dike height for roughness of river channel and further analyze the influence mechanism of submerged dikes for river channel roughness.The results are following conclusions:1) FLUENT software used for the calculation of river flow field of river channel of building submerged dikes is basically feasible; 2) After the arrangement of submerged dikes,the water velocity distribution is similar to the velocity distribution of the original river; 3) When a flow pass river channel, river channel roughness will increase,while dikes'spacing reduce for the same water cross section; 4) In submerged dikes'sections, river channel roughness is largely influenced by variation of the ratio between the water depth and dike height; the downstream of submerged dikes'sections, river channel roughness is little influenced.5) The inference on river channel roughness for the downstream of submerged dikes'sections can be ignored, the roughness of submerged dikes' downstream is equals to the roughness of the original channel; 6) when the dikes'spacing is unchanged, river channel roughness will reduce when the ratio between the water depth and dike height increased,for the same water cross section; 7) For the same dikes'spacing and the ratio between the water depth and dike height, river channel roughness will reduce along the river channel; The submerged dikes'inference on river channel roughness is reduced along the river channel; when the ratio between the depth and dam height reached to a certain level,the river channel roughness will no longer changed along the river channel; 8) When a flow pass river channel, with the decrease of the dikes'spacing, the Margin of becoming large Of flow velocity from upstream to downstream increases; 9) The velocity vector of water positive side of the submerged dike is scattered and small; the dorsal surface of the submerged dike, the velocity vector is concentrated and great; the dorsal surface of the submerged dike,there is whirlpool(Negative pressure area); 10) The velocity vector equivalent lines of water positive side of the submerged dike is few and covers a large area and the velocity is small; The velocity vector equivalent lines of the dorsal surface of the submerged dike is concentrated and great and covers large area.