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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

We performed large-eddy simulations (LES) of forced impinging jets over smooth and rough surfaces, containing large-scale, azimuthal vortices generated by the enhanced primary instability in the jet shear layer. The interaction between these vortices and the turbulence in the wall jet that is formed downstream of the impingement region determines their rate of decay. To explore the surface-roughness effects on the evolution of the vortices, sand-grain-like surfaces are generated using uniformly distributed but randomly oriented ellipsoids. The flow is compared to our previous LES of jets impinging on a smooth surface. In spite of the severe modification caused by the roughness on the near-wall flow, the vortex development is not significantly altered. Slightly faster decay of the primary vortices is observed in the rough-wall case compared to the smooth-wall one; the secondary vortex that detaches from the wall and is lifted up has larger vorticity. The highly disturbed near-wall flow is advected outward and affects the evolution of the primary vortex for a longer period during the vortex interaction. The robust turbulent generation mechanism in the outer shear layer, however, mitigates the changes in vortex behaviour. The momentum deficit and the enhancement of turbulence due to the surface roughness play a key role during this process.