DIFFUSION BEHIND A LINE SOURCE IN GRID TURBULENCE.

Abstract

The flow considered is the thermal wake downstream of a fine heated wire in grid turbulence. The inability of generally-applicable turbulent diffusion models and second-order closures to calculate the mean and variance of the temperature is reviewed. Calculations based on the transport equation for the joint probability density function (pdf) of velocity and temperature show good agreement with measurements of mean temperature but not with those of the variance. Better calculations of the variance are obtained with a method based on the joint pdf conditional on the lateral velocity at the source.