On the destruction coefficients for slightly heated decaying grid turbulence

摘要

In slightly heated grid turbulence, the mean turbulent kinetic energy and passive-scalar variance dissipation rates, 〈ε〉 and 〈x〉, decay according to power laws. The isotropic forms of the transport equations for 〈ε〉 and 〈x〉 suggest that the turbulent mixing (power-law) decay rates depend on the evolution of the ratios G/R_(λ_u) and G_θ/R_(λ_u), where G and G_θ are the destruction coefficients of 〈ε〉 and 〈x〉, respectively, and R_(λ_u) is the Taylor microscale Reynolds number (λ_u is the Taylor microscale). The present measurements and previously published data for grid turbulence show that both C and G_θ increase with R_(λ_u) but the ratios G/R_(λ_u) and G_θ/R_(λ_u), approach constant values. While G_θ/R_(λ_u) is nearer to its asymptotic state than G/R_(λ_u), both ratios appear to reach their asymptotic states as R_(λ_u) approaches 10~3. When this occurs, both velocity and scalar fields should be completely self-preserving.