On the destruction coefficients for slightly heated decaying grid turbulence

•Both G & Gt (destruction coeffs.) increase with Rl (Taylor microscale Reynolds No.).•The ratios G/Rl & Gt/Rl approach constant values when Rl is increased.•The ratio Gt/Rl is nearer to its asymptotic state than the ratio G/Rl.•Both G/Rl & Gt/Rl tend to reach their asymptotic states as Rl approaches 1000.

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/RλuG/Rλu and Gθ/RλuGθ/Rλu, where G and Gθ are the destruction coefficients of 〈∊〉 and 〈χ  〉, respectively, and RλuRλu 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 RλuRλu but the ratios G/RλuG/Rλu and Gθ/RλuGθ/Rλu approach constant values. While Gθ/RλuGθ/Rλu is nearer to its asymptotic state than G/RλuG/Rλu, both ratios appear to reach their asymptotic states as RλuRλu approaches 103. When this occurs, both velocity and scalar fields should be completely self-preserving.