DIRECT NUMERICAL SIMULATION OF UNSHEARED TURBULENCE DIFFUSING TOWARDS A FREE-SLIP OR NO-SLIP SURFACE

Abstract

The physics involved in the interaction between statistically steady, unsheared turbulence and a blocking surface is highly dependent on the precise nature of the surface, i. e. whether it is a free-slip surface or a solid wall. In this paper, we use direct numerical simulation to investigate the differences between these two situations, the original flow configuration introduced by Campagne et al. (2006a,2006b) has been used as a basis for this comparative study. Two simulations have been performed with strictly identical numerical and physical parameters except for the dynamic boundary condition at the plane surface which is either free-slip (free surface) or no-slip (solid wall). We show that the extent of the blocking effect (outer layer) is strictly the same in both cases. The precise nature of the dynamic boundary condition only influences the inner layers. Both flow configurations have been fully documented including the Reynolds-stress budgets. The differences in the intercomponent energy transfer (pressure-strain correlations) are thoroughly investigated. It is shown that the transfer, although slightly larger in the solid wall case, is a significant contributor to both budgets: the slight difference may be attributed to viscous effects as suggested by Perot and Moin (1995). This is obviously not the case for the net level of the correlation. We suggest that this level − representative of the splat/antisplat imbalance in the Perot-Moin phenomenology − is a consequence of the dissymmetry in the interacting turbulent field.