The radial wall jet is a flow configuration that combines the radial jet and the wall jet. This article presents a simulation of the radial wall jet by applying the transition Shear-Stress Transport ( SST) model. Tanaka's experimental data are used for validation. The computed velocity profiles agree well with the experimental ones. The distributions of the velocity on cross-sections show a similarity in the main region and the profiles are different with those of the free radial jet or the wall jet, because the presence of the wall limits the expansion of the jet. By introducing the equivalent nozzle width, the maximum velocity decays and the half-width distributions are normalized, respectively. In addition to compare the flow field with experiments, this paper also analyzes the dilution effect of radial wall jets in terms of the concentration distributions. The concentrations on the wall keep constant within a certain distance from the nozzle. And the concentration distributions also show a similarity in the main region. Both the decays of the maximum concentration and the distributions of the concentration half-width fall into a single curve, respectively. The dilution effect of radial wall jets is thus verified.
LI Zhi-wei HUAI Wen-xin QIAN Zhong-dong ZENG Yu-hong YANG Zhong-hua
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 article summarizes previous studies on the flow in open channels with rigid vegetation, and constructs a mathematical model for submerged and emerged rigid vegetation. The model involves the forces balance in the control volume in one-dimensional steady uniform flow. For submerged vegetation, the whole flow is divided into four regions: external region, upper vegetated region, transition region and viscous region. According to the Karman similarity theory, the article improves the mixing length expression, and then gives an analytical solution to predict the vertical distribution of stream-wise velocity in the external region. For emerged vegetation, the flow is divided into two region: outer region and viscous region. In the two circumstances, the thicknesses of each region are determined respectively. The comparison between the calculated results and our experimental data and other researchers' data proves that the proposed model is effective.
The erosion of loose beds by submerged circular impinging vertical turbulent jets is simulated using an Eulerian two-phase model which implements Euler-Euler coupled governing equations for fluid and solid phases, and a modified k-ε turbulence closure for the fluid phase. Both flow-particle and particle-particle interactions are considered in this model. The predictions of eroded bed profiles agree well with previous laboratory measurements and self-designed experiments. Analysis of the simulated results reveals that the velocity field of the jet water varies with various scouring intensities, that the scour depth and shape are mainly influenced by the driving force of the water when the density, diameter and porosity of the sand are the same, and that the porosity is an important contributor to sediment erosion. In this study, the scour depth, the height of dune and the velocity of the pore water increase with increasing porosity.
QIAN ZhongDong1, HU XiaoQing1, HUAI WenXin1 & XUE WanYun1 State Key Laboratory of Water Resources and Hydropower Engineering Science, Wuhan University, Wuhan 430072, China
This article applies the realizable k-ε model to simulate the buoyant wall jet and gives the results of cling length,centerline trajectory and temperature dilutions at certain sections.The comparison between the numerical results and Sharp's experimental data indicates that the model is effective in estimating velocity distribution and temperature dilutions.The velocity profiles at the cental plane and z-plane both show a strong similarity at certain distance from the nozzle,and the distributions of velocity and temperature dilutions also exhibit a similarity along the axial direction at centerline in the near-field.Based on the results,the article gives the corresponding relationships between the distance and the dilutions of velocity and temperature,which is useful in predicting the behavior of the wall buoyant jet.
This article discusses the transverse distributions of the depth averaged velocity and the Reynolds stress in a steady uniform flow in partially vegetated rectangular channels.The momentum equation is expressed in dimensionless form and solved to obtain the depth averaged velocity.The analytical solution of the velocity in dimensionless form shows that the depth-averaged velocity is determined by gravity and its distribution is mainly determined by the frictions due to water or vegetations.The analytical solution of the Reynolds stress is also obtained.A relationship between the second flow and the inertia is established and it is assumed that the former is proportional to the square of the depth averaged velocity.The Acoustic Doppler Velocimeter(Micro ADV) was used to measure the steady uniform flow with emergent artificial rigid vegetation.Comparisons between the measured data and the computed results show that our method does well in predicting the transverse distributions of the stream-wise velocity and the Reynolds stress in rectangular channels with partially vegetations.
