Scrutinizing URANS in Shedding Flows: The Case of Cylinder in Cross-Flow in the Subcritical Regime
| Autor: | Kemal Hanjalic, E. Palkin, Rustam Mullyadzhanov, M. Hadžiabdić |
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| Rok vydání: | 2016 |
| Předmět: |
General Chemical Engineering
Flow (psychology) General Physics and Astronomy Reynolds number Laminar flow 02 engineering and technology Mechanics Reynolds stress Vortex shedding 01 natural sciences 010305 fluids & plasmas Physics::Fluid Dynamics Stress (mechanics) symbols.namesake 020303 mechanical engineering & transports 0203 mechanical engineering 0103 physical sciences Turbulence kinetic energy symbols Physical and Theoretical Chemistry Reynolds-averaged Navier–Stokes equations Mathematics |
| Zdroj: | Flow, Turbulence and Combustion. 97:1017-1046 |
| ISSN: | 1573-1987 1386-6184 |
| DOI: | 10.1007/s10494-016-9772-z |
| Popis: | To unravel the widespread perception that the RANS (Reynolds-averaged Navier-Stokes) concept is unreliable in predicting the dynamics of separated flows, we assessed the performance of two RANS closure levels, the linear eddy-viscosity (LEVM) and the second-moment (Reynolds stress, RSM) approaches in a massively separated generic flow over a bluff body. Considered is the canonical, zero-turbulence, cross-flow over an infinite cylinder with reference to our LES and the available DNS and experiments at two Reynolds numbers, Re = 3.9 × 103 and 1.4 × 105, both within the sub-critical regime with laminar separation. Both models capture successfully the vortex shedding frequency, but the low frequency modulations are detected only by the RSM. At high Reynolds numbers the RSM is markedly superior to the LEVM showing very good agreement with the LES and experimental data. The RSM, accounting naturally for the stress anisotropy and phase lag between the stress and strain eigenvectors, is especially successful in reproducing the growth rate of the turbulent kinetic energy in the initial shear layer which proved to be crucial for accurate prediction of the separation-induced transition. A scrutiny of the unsteady RANS (URANS) stress terms based on the conditional phase-averaged LES data shows a remarkable similarity of the normalized coherent and stochastic (modeled) stress components for the two Reynolds numbers considered. The mixed (cross) correlations, while non-negligible at the low Re number, diminish fast relative to the stochastic ones with increasing Reynolds number and, in the whole, are not significant to undermine the URANS concept and its applicability to high Re flows of industrial relevance. |
| Databáze: | OpenAIRE |
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