A particle image velocimetry was used to study shallow open channel turbulent flow over d-type and k-type transverse ribs of square, circular, and semi-circular cross sections. The ratio of boundary layer thickness to depth of flow varied from 50% to 90%. The mean velocities and turbulent quantities were evaluated at the top plane of the ribs to characterize interaction between the cavities and overlying boundary layer. It was found that the overlying boundary layer interacts more strongly with k-type cavities than observed for d-type cavities. The profiles of the mean velocities and turbulent statistics were then spatially averaged over a pitch, and these profiles were used to study the effects of rib type and cross section on the flow field. The mean velocity gradients were found to be non-negligible across the boundary layer, and the implications of this observation for momentum transport, eddy viscosity, and mixing length distributions are discussed. The results show that the skin friction coefficient, Reynolds stresses and mixing length distributions are independent of rib cross section for d-type. For the k-type ribs, significant variations in skin friction coefficient values, mean flow, and turbulence fields are observed between square ribs and circular/semi-circular ribs.

Three‐phase (G/L/S) horizontal pipe flow data collected from the literature are used to evaluate the performance of a number of correlations designed to predict the pipeline pressure gradient. In the present study, a number of popular two‐phase gas–liquid pressure loss correlations were modified for three‐phase flow predictions. The primary modification is to assume that the slurry (L/S) mixture behaves as a singlephase. The modified Dukler and the Beggs and Brill correlations did not provide accurate estimates of the three‐phase pressure gradients. When the classical Lockhart–Martinelli (L–M) correlation was used, along with a kinematic friction loss model to calculate the slurry (L/S) superficial flow pressure gradient, accurate predictions of the three‐phase (G/L/S) pressure gradient were obtained provided the slurry did not exhibit non‐Newtonian behaviour and that Coulombic (sliding bed) friction was negligible. Additional experiments should be conducted before the improved version of the L–M correlation is applied to commercial installations with pipe diameters greater than 100 mm.

A numerical investigation of two-phase solid-liquid (slurry) flow in horizontal pipes has been carried out. Simulations of concentrated slurry flows in pipes 0.0515 m and 0.15 m in diameter were performed using the two-fluid approach implemented in the commercial CFD code, ANSYS CFX. Mixtures of monosized and bimodal particle sizes were tested. Several test cases were investigated to predict particle velocity- and concentration-distributions and frictional pressure gradients. The effects of turbulence model selection, dispersed phase wall boundary conditions, and interphase force terms on model performance were evaluated. The selection of turbulence model had a significant impact on the dispersed phase velocity and concentration distributions. Comparison of simulations with benchmark experimental data shows clearly that for the relatively small particle sizes (∼100 microns), poor solids concentration profile predictions are obtained if the turbulent dispersion force is not included. In general, very good agreement between numerical and experimental results was observed.

Experiments were performed in a 265 mm diameter pipe loop with sand‐in‐water slurries (d50 = 0.371 mm). In situ solids volumetric concentrations ranging from 20–40 % by volume (0.20–0.45 L/L) and mixture velocities up to 6 m/s were tested. Measurements of the instantaneous and average solids velocity and turbulent intensity profiles across the centreline diameter of the pipe were obtained using a particle velocity probe. A CFD package, ANSYS CFX 14, was used to perform numerical simulations. Solids turbulent intensities were found to be greater near the bottom of the pipe where solids concentrations are typically higher and significant particle‐pipe wall interactions occur. The agreement between the numerical results and the experimental data was found to be concentration dependent, with relatively closer agreement at lower concentrations.

No abstract

In the present study, both experimental and numerical techniques were employed to study three-dimensional laminar wall jet flows. The wall jet was created using a circular pipe of diameter 7×10−3 m and flows into an open water tank. The inlet Reynolds numbers based on the pipe diameter and jet exit velocity were 310 and 800. A particle image velocimetry (PIV) was used to conduct detailed measurements at various streamwise-transverse and streamwise-spanwise planes. The complete nonlinear incompressible Navier–Stokes equation was also solved using a collocated finite volume based in-house computational fluid dynamics (CFD) code. The computation was performed for three inlet Reynolds numbers, namely, 310, 420, and 800. From the PIV measurements and CFD results, velocity profiles and jet half-widths were extracted at selected downstream locations. It was observed that the numerical results are in reasonable agreement with the experimental data. The distributions of the velocities, jet spread rates, and vorticity were used to provide insight into the characteristics of three-dimensional laminar wall jet flows.

A numerical investigation of turbulent flow in a draft tube with and without an opening (slot) in the top of each of its three outlet channels is presented. A commercial CFD code, CFX-5, is used to solve the Reynolds-averaged Navier-Stokes equations and a standard k-ε turbulence model with a scalable wall-function. The case for no slots was compared with the cases of three mass flow rates into the slots. The results demonstrate that values of the overall pressure coefficient and velocity head obtained for various slot mass flow rates are not significantly different. The flow into the slots, however, creates different amounts of localised recirculation and backflow in the individual outlet channels formed between the two pier noses. RÉSUMÉCet article présente une étude numérique de l'écoulement turbulent dans une chambre d'aspiration avec et sans ouverture (fente) sur le dessus de chacun de ses trois canaux de sortie. Un code commercial de dynamique des fluides, CFX-5, est utilisé pour résoudre les équations de Navier-Stokes en moyenne de Reynolds avec un modèle standard de turbulence k-e et une fonction de paroi ajustable. Le cas sans fentes a été comparé aux cas avec trois débits unitaires de masse dans les fentes. Les résultats montrent que les valeurs du coefficient de pression global et de la vitesse acquise pour différents débits unitaires de fente ne sont pas sensiblement différentes. L'écoulement dans les fentes, crée cependant différentes quantités de recirculation et de refoulement localisés dans les canaux de sortie formés entre les deux nez de pilier.

No abstract