DOI: 10.1615/TSFP6
USE OF LAGRANGIAN STATISTICS FOR THE DIRECT ANALYSIS OF THE TURBULENT CONSTITUTIVE EQUATION
RESUMO
Turbulence models often involve Reynolds averaging, with a closure providing the Reynolds stress u'v' as function of mean velocity gradients du/dy, through a turbulence constitutive equation (equation 1). The main limitation of this linear closure is that it rests on an analogy with kinetic theory. For this analogy to be valid there has to be scale separation. The aim of this work is to better understand this hypothesis from a microscopic point of view. Therefore, fluid elements are tracked in a turbulent channel flow. The flow is resolved by direct numerical simulation (DNS). Statistics on particle trajectories ending on a certain distance yo from the wall are computed leading to estimations of the turbulent mixing length scale and the Knudsen number. Comparing the computed values to the Knudsen number in the case of scale separation we may know in which region of the flow and to what extent the turbulence constitutive equation (equation 1) is not verified.