Etude expérimentale des structures cohérentes de la turbulence de paroi à grand nombre de Reynolds

Experimental study of coherent structures in wall turbulence at high Reynolds number

Laboratoire de Mécanique de Lille, Boulevard Paul Langevin, 59655 Villeneuve d'Ascq Cedex, France

Abstract

The study of the turbulence of boundary layer at high Reynolds number (R_q =[7500,20600]) is tackled experimentaly with velocity measurements from Hot Wire Anemometry (HWA) and Particle Image Velocimetry (PIV). In a first step, the main statistical quantities of the flow was computed for various Reynolds numbers, as a function of the wall distance, by using temporal sequences from HWA measurements. These are mainly statistical quantities at one point, such as mean velocity, Reynolds tensor and probability density functions. Statistical quantities at two points, such as temporal correlations and power spectra, are also available. In a second step, the principal coherent structures of the flow was identified and quantified by using velocity maps from PIV measurements. These are eddy structures, sweeps, ejections, streaks and bulges. Spatial correlations and Proper Orthogonal Decomposition confirmed the presence of these coherent structures. Mathematical morphology brought some informations about their scale, their form, their weight and their possible cross-relationships which organize the wall turbulence.