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Hybrid RANS/LES of plane jets impinging on a flat plate at small nozzle-plate distances

Kubacki S., Rokicki J., Dick E., Degroote J., Vierendeels J.

Archives of Mechanics

2013

Vol. 65, nr 2

143--166

A k-ω based hybrid RANS/LES (Reynolds-averaged Navier-Stokes/large eddy simulation) model is tested for simulation of plane impinging jets at various nozzle-plate distances (H/B, where H is the distance and B is the slot's width) and various Reynolds numbers (based on the slot's width and the velocity in the symmetry plane). The studied combinations are H/B=2 for Re=10000, H/B=4 for Re=18000 and H/B=9.2 for Re=20000. The focus is on small distance of the nozzle exit to the plate. In LES mode, the hybrid RANS/LES model uses two definitions of the local grid size, one based on the maximum distance between the cell faces in the destruction term of the turbulent kinetic energy equation and one based on the cube root of the cell volume in the eddy-viscosity formula. This allows accounting for flow inhomogeneity on anisotropic grids. In RANS mode, the hybrid model turns into the newest version of the k-ω model by Wilcox.

Hybrid RANS/LES computation of plane impinging jet flow

Kubacki S., Rokicki J., Dick E.

Archives of Mechanics

2011

Vol. 63, nr 2

117-117

Flow characteristics are presented of simulation results of plane impinging jets at high nozzle-plate distances, with two k-? based hybrid RANS/LES (Reynolds Averaged Navier–Stokes/Large–Eddy Simulation) models and a k-? RANS model. The first hybrid RANS/LES model is obtained by substitution of the turbulent length scale by the local grid size in the destruction term of the turbulent kinetic energy equation and in the definition of the eddy-viscosity. The second hybrid model is obtained by a latency factor in the definition of the eddy-viscosity. The RANS model overpredicts the length of the jet core region, caused by too weak turbulent mixing in the shear layers of the jet. This results in erroneous near-wall shear stress along the impingement plate. The hybrid RANS/LES models overcome the deficiency of the RANS model. Further, the hybrid models represent the flow with much more detail. For instance, the Görtler vortices are well reproduced in the stagnation flow region by the hybrid RANS/LES models.