Experimental study of the SGS pressure-strain-rate correlation in the convective atmospheric surface layer

The subgrid-scale (SGS) stress is studied using measurement data obtained in the atmospheric surface layer during the Advection Horizontal Array Turbulence Study (AHATS) field program, which notably includes measurement of the resolvable- and subgrid-scale pressure. The data are used to study challenges met in large eddy simulation, particularly modeling of the SGS pressure-strain-rate correlation. Our previous study has shown that this term is strongly dependent on the large scale dynamics of the convective atmospheric surface layer, namely updrafts, downdrafts, and wall blocking of the energy-containing eddies [Nguyen et al., J Fluid Mech 729, 2013].

In the present study, we analyze the terms in the transport equation of the SGS stress, conditioned on the resolvable-scale velocity, for different filter scales and atmospheric stability. The results show that the pressure destruction term in the budget of the SGS shear stress plays the usual role of return-to-isotropy and generally counters the trends of the conditional production for all filter scales and unstable conditions. In contrast, the pressure-strain-rate correlations in the budgets of the normal SGS stress components can be the main cause of anisotropy of the SGS stress under convective conditions, depending strongly on the resolvable-scale velocity. These effects are most significant at large filter scales and have strong implications for modeling the near-wall SGS pressure-strain-rate correlation.