The interaction between a plane wall jet and a parallel offset jet is studied through the Large Eddy Simulation (LES).In order to compare with the related experimental data,the offset ratio is set to be 1.0 and the Reynolds number Re is 1.0×10 4 with respect to the jet height L and the exit velocity 0 U.The Finite Volume Method (FVM) with orthogonal-mesh (6.17×10 6 nodes) is used to discretize governing equations.The large eddies are obtained directly,while the small eddies are simulated by using the Dynamic Smagorinsky-Lily Model (DSLM) and the Dynamic Kinetic energy Subgrid-scale Model (DKSM).Comparisons between computational results and experimental data show that the DKSM is especially effective in predicting the mean stream-wise velocity,the half-width of the velocity and the decay of the maximum velocity.The variations of the mean stream-wise velocity and the turbulent intensity at several positions are also obtained,and their distributions agree well with the measurements.The further analysis of dilute characteristics focuses on the tracer concentration,such as the distributions of the concentration (i.e.,0 C /C or /m C C),the boundary layer thickness δ c and the half-width of the concentration c b,the decay of the maximum concentration (0 /m C C) along the downstream direction.The turbulence mechanism is also analyzed in some aspects,such as the coherent structure,the correlation function and the Probability Density Function (PDF) of the fluctuating velocity.The results show that the interaction between the two jets is strong near the jet exit and they are fully merged after a certain distance.
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.
