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Reactive control of large-scale structures in a turbulent wake

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Title: Reactive control of large-scale structures in a turbulent wake
Author: Varon, Eliott; Aider, Jean-Luc; Eulalie, Yoann; Edwige, Stephie; Gilotte, Philippe
Abstract: The dynamics of large-scale structures in the near wake downstream a square-back Ahmed body [1] are experimentally studied then controlled at Re=3.9 ×10e5, based on the body height. The barycenters of the rear pressure and the recirculation intensity are tracked based respectively on pressure and PIV measurements. Both quantities track large-scale structures and exhibit strong bimodal distributions characteristic of a stochastic behavior [4]. However their low frequencies dynamics seem to contain a chaotic aspect which is characterized through standard properties of such dynamics: structure function, correlation dimension, largest Lyapunov exponent and telegraph-like signal. Using asymmetric jets tangentially to the upper rear surface of the bluff body a reactive control is applied, based on the recirculation intensity position as control variable. The jets can be set to continuous or pulsed mode (cµ = 0.03%). An optical ?ow algorithm computes in real-time the velocity ?elds [2, 3], which enables such experimental approach. The controlled ?ow results in more stabilized bi-modal dynamics. The wake switches between two highly preferred modes with a shorter transition time. The dynamics are ?xed by the time scale of the control law. [1] S.R. Ahmed, G. Ramm, and G. Faltin. Some Salient Features Of The Time-Averaged Ground Vehicle Wake. Technical report, SAE Technical Paper 840300, 1984. [2] F. Champagnat, A. Plyer, G. Le Besnerais, B. Leclaire, S. Davoust, and Y. Le Saint. Fast and accurate piv computation using highly parallel iterative correlation maximization. Exp. Fluids, 50:1169?1182, 2011. [3] N. Gautier and J.-L. Aider. Real-time planar ?ow velocity measurements using an optical ?ow algorithm implemented on GPU. J. Vis., 18:277?286, 2015. [4] M. Grandemange, M. Gohlke, and O. Cadot. Turbulent wake past a three-dimensional blunt body. Part 1. Global modes and bi-stability. J. Fluid Mech., 722:51?84, 2013.
Subject: corps de Ahmed; contrôle de sillage; turbulence de sillage; Dynamique chaotique; flot optique
Publisher: AFM, Association Française de Mécanique
Date: 2017

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  • Président comité d'organisation : Thomas Rougelot
  • Président du conseil scientifique : Jianfu Shao
  • Co-Présidents du conseil scientifique : Gilmar Mompean et Eric Markiewicz
  • Editeur : Association Française de Mécanique
  • ISSN : 2491-715X (en ligne)
  • Contact : cfm2017