DECAY OF ISOTROPIC TURBULENCE AT LOW-REYNOLDS-NUMBER

Decay of isotropic turbulence is computed using direct numerical simulations. Comparisons with experimental spectra at moderate and low Reynolds numbers (R(lambda) < 70) show good agreement. At moderate to high Reynolds numbers (R(lambda) > 50), the spectra are found to collapse with Kolmogorov scaling at high wave numbers. However, at low Reynolds numbers (R(lambda) < 50) the shape of the spectra at the Kolmogorov length scales is Reynolds number dependent. Direct simulation data from flowfields of decaying isotropic turbulence are used to compute the terms in the equation for the dissipation rate of the turbulent kinetic energy. The development of the skewness and the net destruction of the turbulence dissipation rate in the limit of low Reynolds numbers are presented. The nonlinear terms are found to remain active at surprisingly low Reynolds numbers.