Abstract
The direct interaction approximation suggested by Kraichnan is used to study the scalar mixing problem in a stationary isotropic turbulent velocity field. The main part of this paper deals with the decay of scalar quantity fluctuations in a simplified stationary velocity field. The numerical integration of the direct interaction equations was carried out with several different initial spectra for Peclet numbers of 50 and 500. The results seem to demonstrate naturalness of the direct interaction approximation; however, no comparison with experiments can be made at present.

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