(Received 10 September 1990; accepted 5 November 1990)
The inertial-conductive subrange spectrum of a passive temperature field of a fluid of small Prandtl number is determined by large-eddy simulation. Results for simulations of both freely decaying and forced turbulence are presented. In the simulations of freely decaying turbulence, a subgrid model is used to simulate a decaying turbulent velocity field with a k5/3 inertial subrange energy spectrum convecting eight different decaying temperature fields with well-resolved conductive subranges. In the simulations of forced turbulence, a subgrid model is again used to simulate an inertial subrange vbelocity field; however, the velocity field is now forced at the lowest wave numbers of the simulation, and an external uniform mean temperature gradient is imposed. Statistically stationary velocity and temperature fluctuations are generated. The results of the decaying and forced simulations are in excellent agreement with the Batchelor, Howells, and Townsend (BHT) [J. Fluid Mech. 5, 134 (1959)] k17/3 spectrum in the far inertial-conductive subrange, whereas significant departures from the BHT spectrum are observed in the near inertial-conductive subrange.
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