Energy transfer and dissipation in forced isotropic turbulence*

A model for the Reynolds number dependence of the dimensionless dissipation rate $C_{\varepsilon}$ is derived from the dimensionless K\'{a}rm\'{a}n-Howarth equation, resulting in $C_{\varepsilon}=C_{\varepsilon, \infty} + C/R_L$, where $R_L$ is the integral scale Reynolds number. The coefficients $C$ and $C_{\varepsilon,\infty}$ arise from asymptotic expansions of the dimensionless second- and third-order structure functions. The model equation is fitted to data from direct numerical simulations (DNS) of forced isotropic turbulence for integral scale Reynolds numbers up to $R_L=5875$ ($R_{\lambda}=435$), which results in an asymptote for $C_\varepsilon$ in the infinite Reynolds number limit $C_{\varepsilon,\infty} = 0.47 \pm 0.01$. Since the coefficients in the model equation are scale-dependent while the dimensionless dissipation rate is not, we modelled the scale dependences of the coefficients by an \emph{ad hoc} profile function such that they cancel out, leaving the model equation scale-independent, as it must be. The profile function was compared to DNS data to very good agreement, provided we restrict the comparison to scales small enough to be well resolved in our simulations.