DECAY OF ISOTROPIC TURBULENCE AT LOW-REYNOLDS-NUMBER

Decay of isotropic turbulence is computed using direct numerical simul ations. Comparisons with experimental spectra at moderate and low Reyn olds 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 l ength scales is Reynolds number dependent. Direct simulation data from flowfields of decaying isotropic turbulence are used to compute the t erms in the equation for the dissipation rate of the turbulent kinetic energy. The development of the skewness and the net destruction of th e turbulence dissipation rate in the limit of low Reynolds numbers are presented. The nonlinear terms are found to remain active at surprisi ngly low Reynolds numbers.