Statistical and Spectral Analysis of Turbulence

Abstract

A.1 Turbulence Properties Flows qualified as " turbulent " can be found in most fields that make use of fluid mechanics. These flows posses a very complex dynamics whose intimate mechanisms and repercussions on some of their characteristics of interest to the engineer should be understood in order to be able to control them. The criteria for defining a turbulent flow are varied and nebulous because there is no true definition of turbulence. Among the criteria most often retained, we may mention [150]: – the random character of the spatial and time fluctuations of the veloci-ties, which reflect the existence of finite characteristic scales of statistical correlation (in space and time); – the velocity field is three-dimensional and rotational; – the various modes are strongly coupled, which is reflected in the non-linearity of the mathematical model retained (Navier–Stokes equations); – the large mixing capacity due to the agitation induced by the various scales; – the chaotic character of the solution, which exhibits a very strong depen-dency on the initial condition and boundary conditions.