ISOTROPIC TURBULENCE - IMPORTANT DIFFERENCES BETWEEN TRUE DISSIPATIONRATE AND ITS ONE-DIMENSIONAL SURROGATE

The one-dimensional surrogate (1D) of energy dissipation rate has ofte n been used in place of the true one in investigations of the Kolmogor ov refined similarity hypothesis and the multifractal nature of isotro pic turbulence. Direct numerical simulations, reported here, show that the use of the 1D surrogate can lead to fundamental changes in statis tics. The conditional and unconditional probability densities of the K olmogorov variable built from the true dissipation are never bimodal a nd always nearly Gaussian.