Abstract
The capture precision of the free surface of an open-channel with a water-air interface directly affects the calculation precision of flow field characteristics and general characteristics of the flow. Significant research effort has been devoted to Level Set since its creation, although the relevant research is mainly limited to bubble or droplet movement. In this paper, Level Set method is applied to a two-dimensional numerical simulation of open-channel turbulence, while a new numerical model is proposed and multispot synchronized experimental data are applied to the validation of numerical model. In addition, the model is used to study the flow field characteristics and general characteristics of open-channel flow, which have a water-level lowering curve. The study shows that (1) a semilogarithm zone of vertical distribution of longitudinal velocity is still present amid the transition of flow from nonuniform to uniform, and the depth-averaged velocity and wall shear stress increase along the flowing path. (2) both the energy loss coefficient and roughness coefficient of the flow at nonuniform flow region are greater than the respective values at uniform flow region, and the magnitude of the deviation is relevant to the magnitude of the flow deviation from uniform flow stage.
Highlights
The flow in natural river course and artificial open-channel belongs to open-channel flow, which is characterized by the existence of free surface [1,2]
The following conclusions can be obtained from the figure: (1) under simulated working conditions, the water depth and depth-averaged velocity of nonuniform open-channel flow approximately change to the corresponding value of uniform flow at x/h0 = 6~8 of longitudinal location and (2) under the same bottom slope conditions, the higher the Froude number is, the shorter the longitudinal length is required, which is the length required for nonuniform flow reach to uniform state
We established the vertical two-dimensional numerical based on Level Set method
Summary
The flow in natural river course and artificial open-channel belongs to open-channel flow, which is characterized by the existence of free surface (water-air interface) [1,2]. Rigid-lid and VOF are the two common methods of water surface handling at present [15,16,17] The former is adopted to address a free surface problem of steady uniform-flow, but some researchers [11] pointed out that the reliable results may not be obtained by rigid-lid under certain conditions. The following issues are addressed in order to guarantee precision in the calculations: (a) the water flow-air density ratio ρw/ρa = 828.4 and viscosity coefficient ratio μw/μa = 55.5 may destabilize the calculation given the high ρ-μ difference on both sides of the free surface. (b) After a certain time increment, function φ(x, y) no longer meets Eq (1) defined as the symbolic distance characteristics in the numerical calculation In this regard, φ(x, y) at the end of each stage is initialized to meet the requirement, a solution to the following initial value problem:. The computational details of the reinitialization are given in S3 Appendix
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