Interaction of inner and outer layers in plane and radial wall jets

Abstract

Large eddy simulations of turbulent radial and plane wall jets were performed at different Reynolds numbers using the Lagrangian dynamic eddy viscosity subgrid-scale model. The results were validated with experimental data available in the literature. Compared to the plane ones, the radial wall jets have an extra direction for expansion, which causes faster decay rates. Thus, the resulting pressure gradient distributions are different. However, the comparison of the results with the turbulent boundary layers under adverse and favourable pressure gradients reveals that these pressure gradients are not strong enough to cause any fundamental physical difference between plane and radial wall jets. In both cases, the local Reynolds number is an important determining factor in characterisation of the flow. The joint probability density function analysis shows that the local Reynolds number determines the level of intrusion of the outer layer into the inner layer: the lower the local Reynolds number, the stronger is the interaction of the inner and outer layers. These results can be used to clarify the scatter of the reported log-law constants in the literature.Keywords: plane wall jet; radial wall jet; logarithmic law of the wall; large eddy simulation; inner/outer layer interaction

Flow characteristics of an offset jet over a surface mounted square rib

“…As the jet developed, the high turbulence levels within the outer shear layer displaced negative −uv towards the bottom of the channel similar to reports by Azim [19] and Abrahamsson et al [20] for a plane wall jet. The present observations indicate an interaction between the inner and outer shear layers of the discharged offset jet similar to reports by Banyassady and Piomelli [21] for a plane wall jet. The occurrence of the CGDP has a significant implications for the ability of turbulence models based on the eddy viscosity concept (which assumes the point of zero shear stress to coincide with y m ) to accurately reproduce the mean flow properties.…”

“…The contours show that the fluctuations are not evenly distributed suggesting the anisotropic nature of the turbulence field. The present shape of the JPDF contour is similar to those reported by Banyassady and Piomelli [21,27] within the inner shear layer of a plane wall jet over smooth and rough surfaces. The WJPDF contours within the inner shear layer show the nearly equal distribution of the various quadrant events and this is not affected by rib position.…”

“…The present results suggest that there is an ejection of low momentum fluid by the outer layer structures towards the wall (Q2 event) and a sweep of high momentum jet towards the outer shear layer (Q4 events). This observation also provide an indication of the interaction between the outer and inner shear layers of the offset jet flow, supporting observations made by Banyassady and Piomelli [21]. This interaction transports positive Reynolds shear stress from the outer shear layer towards the inner shear layer.…”

“…The varied turbulent length scales in the developing region is responsible for the variations observed in the flow dynamics. The shape of the R uu contours in the inner shear layer of the self-similar region resemble those reported for 3D offset jets with no mounted rib, [10], plane wall jets [21,27] and boundary layers. [29] A similar analysis was done for the spatial distribution of the R vv contours (not shown).…”

“…The present observation is similar to previous studies by NyantekyiKwakye et al [10] for the no rib case and Agelinchaab and Tachie [9] for 3D offset jets, as well as plane wall jets over both smooth [19,20] and rough surfaces. [21][22] Mounting a rib within the inner shear layer of the jet deflected the location of −uv = 0 into the outer shear layer in the developing region. Thus, within the developing region, the CGDP occurred within the outer shear layer of the jet but as the jet developed further downstream through the self-similar region, the CGDP occurred in the inner shear layer of the jet.…”