Publication Abstracts

Canuto and Cheng 1997

Canuto, V.M., and Y. Cheng, 1997: Determination of the Smagorinski-Lilly constant CS. Phys. Fluids, 9, 1368-1378, doi:10.1063/1.869251.

The Smagorinsky-Lilly (SL) SGS model νt = (CSΔ)2S yields a constant CS = 0.20-0.22 which is a factor of 2 larger than what is needed in LES calculations; in addition, Deardorff and Hunt et al. suggested empirical corrections to the SL model to account for the effects of stratification and shear. In this paper, we propose an SGS model that naturally includes stratification and shear (recovering the two previous models) and that gives rise to a value of CS ∼ 0.11. The three basic assumptions underlying the SL model are (1) Fickian approximation, b = -2νtS, where b is the Reynolds stress tensor and S is the strain rate tensor, (s) SGS satisfy Kolmogorov law, and (3) local equilibrium, P = ε, where P and ε are the rates of production and dissipation. We avoid (1) by using the most general b = b(S,R) relationship, where R is the vorticity, and (3) by letting the ratio P/ε vary. The most critical ingredient is (2). We derive the energy spectrum E(k) in the presence of buoyancy N and shear S and show that the SGS scales are not Kolmogorov, which sets in only for wave number k ≫ pi/Δ. Integrating over all SGS scales we obtain the turbulent kinetic energy and then construct a new dissipation length l = l(N,S), which we validate in three ways: (a) use of l(N,0) reproduces the empirical SGS model by Deardorff, (b) use of l(0,S) reproduces the empirical SGS model of Hunt et al., and (c) the complete l(N,S) reproduces LES data that no other has been able to explain. Results for CS are as follows. Homogeneous shear: the removal of each of the three approximations is responsible for an almost equal (∼30%) lowering of CS from 0.2 to 0.1. Plane strain: the lack of vorticity makes the Fickian approximation an acceptable one. The lowering of CS is due in equal measure to the removal of (2) and (3) above. The two examples show that even though the numerical value of ∼0.11 may look like a "universal" constant, it is actually the combination of physical processes that differ from flow to flow. That CS is actually a dynamical variable that adjusts itself to each flow has already been observed by previous authors.

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BibTeX Citation

  author={Canuto, V. M. and Cheng, Y.},
  title={Determination of the Smagorinski-Lilly constant CS},
  journal={Physics of Fluids},

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RIS Citation

ID  - ca02200i
AU  - Canuto, V. M.
AU  - Cheng, Y.
PY  - 1997
TI  - Determination of the Smagorinski-Lilly constant CS
JA  - Phys. Fluids
JO  - Physics of Fluids
VL  - 9
SP  - 1368
EP  - 1378
DO  - 10.1063/1.869251
ER  -

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