Published online by Cambridge University Press: 21 April 2006
The influence of buoyancy on the pressure–strain term is calculated approximately by an analytical theory. It is shown that the buoyancy contribution to (ϕij + ϕji)1, the fluctuation part of the pressure–strain term, is approximately equal to the buoyancy contribution which comes from the mean-field part of the pressure–strain term, provided that the mean buoyancy does not vary rapidly in space or time. The latter, but not the former, buoyancy contribution was previously obtained by Launder (1975) and by Zeman & Lumley (1976). Both contributions are shown to be accounted for by use of a single numerical coefficient Cθ*. The value of Cθ* predicted from purely theoretical considerations is 0.7, and a value determined from an experiment is 0.9. The theoretical method has some generality and can be applied to higher than second-order correlations of velocity and temperature fluctuations.