Large-eddy simulation of wall bounded shear flow using the nonlinear disturbance equations

By means of large-eddy simulation, homogeneous turbulence is simulated for neutrally and stably stratified shear flow at gradient-Richardson numbers between zero and one. We investigate the turbulent transport of three passive species which have uniform gradients in either the vertical, downstream or cross-stream direction. The results are compared with previous measurements in the laboratory and in the stable atmospheric boundary layer, as well as with results from direct numerical simulations. The computed and measured flow properties agree with each other generally within the scatter of the measurements. At strong stratification, the Froude number becomes the relevant flow-controlling parameter. Stable stratification suppresses vertical overturning and mixing when the inverse Froude number based on a turn-over timescale exceeds a critical value of about 3. The turbulent diffusivity tensor is strongly anisotropic and asymmetric. However, only the vertical and the cross-stream diagonal components are of practical importance in shear flows. The vertical diffusion coefficient is much smaller than the cross-stream one at strong stratification. This anisotropy is stronger than predicted by second-order closure models. Turbulence fluxes in downstream and cross-stream directions follow classical mixing-length models.

Download Full-text

Preservation of statistical properties in large-eddy simulation of shear turbulence

Journal of Fluid Mechanics ◽

10.1017/s0022112007008609 ◽

2007 ◽

Vol 592 ◽

pp. 471-494 ◽

Cited By ~ 23

Author(s):

P. GUALTIERI ◽

C. M. CASCIOLA ◽

R. BENZI ◽

R. PIVA

Keyword(s):

Shear Flow ◽

Large Eddy Simulation ◽

Energy Production ◽

Longitudinal Velocity ◽

Statistical Properties ◽

Wall Region ◽

Spatial Homogeneity ◽

Eddy Simulation ◽

Large Eddy ◽

Shear Turbulence

We discuss how large-eddy simulation (LES) can be properly employed to predict the statistics of the resolved velocity fluctuations in shear turbulence. To this purpose ana posterioricomparison of LES data against filtered direct numerical simulation (DNS) is used to establish the necessary conditions that the filter scaleLFmust satisfy to achieve the preservation of the statistical properties of the resolved field. In this context, by exploiting the physical role of the shear scaleLS, the Kármán–Howarth equation allows for the assessment of LES data in terms of scale-by-scale energy production, energy transfer and subgrid energy fluxes. Even higher-order statistical properties of the resolved scales such as the probability density function of longitudinal velocity increments are well reproduced, provided the relative position of the filter scale with respect to the shear scale is properly selected. We consider here the homogeneous shear flow as the simplest non-trivial flow which fully retains the basic mechanism of turbulent kinetic energy production typical of any shear flow, with the advantage that spatial homogeneity implies a well-defined value of the shear scale while numerical difficulties related to resolution requirements in the near wall region are avoided.

Download Full-text