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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.

Performance prediction of centrifugal pumps with CFD-tools

Dick E., Vierendeels J., Serbruyns S., Vande Voorde J.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

2001

Vol. 5, No 4

579-594

The CFD code FLUENT, version 5.4, has been used for the flow analysis of two test pumps of end-suction volute type: one of low specific speed and one of medium specific speed. For both, head as a function of flow rate for constant rotational speed is known from experiments. FLUENT provides three calculation methods for analysis of turbomachinery flows: the multiple reference frame method (MRF), the mixing plane method (MP) and the sliding mesh method (SM). In all three methods, the flow in the rotor is calculated in a rotating reference frame, while the flow in the stator is calculated in an absolute reference frame. In the MRF and MP methods steady flow equations are solved, while in the SM method, unsteady flow equations are solved. The SM method does not introduce physical approximations. The steady methods approximate the unsteady interaction between rotor and stator. The cost of the unsteady method is, however, typically 30 to 50 times higher than the cost of the steady methods. It is found that the MRF and MP methods lead to completely erroneous flow field predictions for flows far away from the best efficiency point. This makes the steady methods useless for general performance prediction.