Stochastic backscatter in large-eddy simulations of boundary layers.

*(English)*Zbl 0765.76039Previous large-eddy simulations of high-Reynolds-number boundary layers suffer from a common problem of excessive mean velocity gradients close to the surfaces. Apparently this error is inherent in the Smagorinsky subgrid model. Noting that stochastic backscatter is a physical process which is missing from the Smagorinsky model and which should be important in this region, the backscatter modification is proposed which appears to remedy the problem and leads to improved large-eddy simulations. The magnitude found to give optimum results is an energy backscatter which, where lengthscales are not influenced by walls, has a value of 1.4 times the dissipation, and is equal to that obtained from EDQNM theory for an infinite inertial subrange of J. R. Chasnov [Phys. Fluids A 3, No. 1, 188-200 (1991; Zbl 0718.76050)]. In the case of a passive scalar the results obtained seem to support that the backscatter of half the scalar variance is a relative smaller fraction of the scalar dissipation. The paper has demonstrated a credible cure to a long-standing problem and gives hope that the optimism concerning the many future applications of large-eddy simulation is well founded.

Reviewer: W.-Z.Yang (Taipei)

##### Keywords:

logarithmic flow profiles; turbulent Prandtl number; Smagorinsky subgrid model; EDQNM theory; passive scalar
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\textit{P. J. Mason} and \textit{D. J. Thomson}, J. Fluid Mech. 242, 51--78 (1992; Zbl 0765.76039)

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