The theory of poroelasticity is introduced to study the hydraulic properties of the steady uniform turbulent flow in a partially vegetated rectangular channel.Plants are assumed as immovable media.The resistance caused by vegetation is expressed by the theory of poroelasticity.Considering the influence of a secondary flow,the momentum equation can be simplified.The momentum equation is nondimensionalized to obtain a smooth solution for the lateral distribution of the longitudinal velocity.To verify the model,an acoustic Doppler velocimeter(ADV) is used to measure the velocity field in a rectangular open channel partially with emergent artificial rigid vegetation.Comparisons between the measured data and the computed results show that the method can predict the transverse distributions of stream-wise velocities in turbulent flows in a rectangular channel with partial vegetation.
Results of several Large Eddy Simulations (LES) of open channel flows with non-submerged vegetation are presented in this article. It is shown that the vegetation can make the flow structure in the mainstream direction uniform for both supercritical and subcritical flows. For subcritical flows, the LES results of the ensemble-average of time-averaged velocity distributions at four vertical sections around a single plant are in good agreement with measurements. The velocity sees double peaks at the upper and lower positions of flows. For supercritical flows, the ensemble-average velocities see some discrepancy between LES and measurement results. Some secondary flow eddies appear near the single plant, and they just locate in the positions of the double peaks in stream-wise velocity profiles. It is also found that the vegetation drag coefficient deceases as the Froude number increases.
A two-dimensional numerical model of vertical jet scour was developed based on the turbulent flow theory and jet scour mechanism. In this model,drag force acts as the main reference variable and the critical Shields number acts as the incipient motion criteria of sediment. The morphological change in the bed caused by bed-load transport is simulated using the moving mesh method and the suspended-load is not considered. An experiment investigating vertical clear water jet scour was conducted in the laboratory,and some effective experimental results,such as flow patterns and distribution characteristics of scour pits,were obtained. Numerical simulation of the 2D jet scour was conducted using the same parameters as were used in the flume experiment. The evolution process of the jet scour observed in the experiment was simulated by the new model;validation of the numerical model and the algorithm was conducted. Semi-empirical formulas of the characteristic length of the equilibrium scour hole were deduced based on the results of the experiment and simulation.
HUAI WenXin WANG ZengWu QIAN ZhongDong HAN YaQiong
