Abstract
In slightly heated grid turbulence, the mean turbulent kinetic energy and passive-scalar variance dissipation rates, 〈∊〉 and 〈χ〉, decay according to power laws. The isotropic forms of the transport equations for 〈∊〉 and 〈χ〉 suggest that the turbulent mixing (power-law) decay rates depend on the evolution of the ratios G/Rλu and Gθ/Rλu, where G and Gθ are the destruction coefficients of 〈∊〉 and 〈χ〉, respectively, and Rλu is the Taylor microscale Reynolds number (λu is the Taylor microscale). The present measurements and previously published data for grid turbulence show that both G and Gθ increase with Rλu but the ratios G/Rλu and Gθ/Rλu approach constant values. While Gθ/Rλu is nearer to its asymptotic state than G/Rλu, both ratios appear to reach their asymptotic states as Rλu approaches 103. When this occurs, both velocity and scalar fields should be completely self-preserving.
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