Approximation of the Third Two-Point Moments of the Velocity Field in Isotropic Turbulence

摘要

Different methods for approximating the third two-point moments of the velocity fields entering in the von Karman-Howarth equation are compared using the known experimental results of A. Townsend and R. Stewart, together with the model form of the energy spectrum of turbulence, which makes it possible to approximate the experimentally determined second moments of the velocity field. The latter moments are used for calculating the third two-point moments following the methods proposed by various authors. The calculated results are compared with the experimental data which makes it possible to quantitatively estimate the approximation accuracy. For several models the second-order structure function is calculated from the Kolmogorov equation for the inertial interval. In this case, for the models of K. Hasselmann and Yu.M. Lytkin the power-law dependence D_(LL)(r) ～ r~(2/3) expected for the inertial interval is obtained for the structure function D_(LL) (r).