Temporal vortex tracking in isotropic turbulence

Abstract

An algorithm to allow the temporal vortex tracking of the intense vorticity structures is introduced and applied to direct numerical simulations (DNS) of homogeneous isotropic turbulence (HIT). The algorithm allows the identification of the individual life events of the worms, including events of splits into several structures and of merging between different structures. Results obtained from a relatively small DNS, with Taylor based Reynolds number equal to Reλ = 54, for a simulation lasting more than 6 integral time scales, shows that the complement of the CDF of the life time of the IVS is well approximated by an exponential distribution function. The mean life time of the IVS which is approximately 3.6τη , where τη is the Kolmogorov time, and the birth rate of these structures is close to 4.5/τη (number of new structures per Kolmogorov time). A population model is built to predict the number of existing structures at any time, which gives a number of existing IVS equal to ≈ 16, which agrees well with the results from the DNS.