An Analysis of Closures for Pressure-Scalar Covariances in the Convective Boundary Layer

Abstract

Abstract Perhaps the most commonly used closure in second-moment models of turbulence is Rotta's return-to-isotropy expression, which was originally developed to pararmeterize the pressure-velocity gradient correlation in the Reynolds stress conservation equations. It is not clear that this closure alone is adequate for application to convective turbulence, however, because of the pervasive effects of buoyancy on turbulence structure. We study the closure problem for the pressure covariance in the scalar flux equation using a data set we generated through large-eddy simulation (LES) of a convective boundary layer. We resolve the pressure field into turbulence–turbulence, mean-shear, buoyancy, Coriolis, and subgrid-scale components, and find that the buoyancy and turbulence–turbulence components dominate in the convective boundary layer. The buoyancy contribution to the pressure-gradient/scalar covariance is one-half of the buoyant production term in the flux equation, to a good approximation, while the tu...