INFORMATIVO ABCM Nº 113/07 – Ph. D. Position in Flow Control in Paris

Unite Mixte de Recherche U.M.R.

LABORATOIRE DE
SUPERIEURE DE PHYSIQUE ET
DE CHIMIE MECANIQUE DES
DE LA MILIEUX HETEROGENES

ECOLE PHYSIQUE ET
INDUSTRIELLES VILLE DE PARIS

PhD Thesis proposal
Sept 2007
Urgent

PMMH Laboratory (Physique et Mécanique des Milieux Hétérogènes) – UMR CNRS 7636

Research Team Instability, Control and Turbulence Dr AIDER Jean-Luc, Directeur de Recherche CNRS (aider@pmmh.espci.fr) +33140795852 Dr. WESFREID Jose-Eduardo, Directeur de Recherche CNRS, Directeur du Laboratoire

(wesfreid@pmmh.espci.fr) +33140794445 Adresse : ESPCI
10, rue Vauquelin
75231 Paris cedex 05
France

The PMMH Laboratory from ESPCI (Ecole Supérieure de Physique et Chimie Industrielles de Paris) proposes a PhD thesis on the following subject:

« Study of the interactions between Jet Vortex Generators (JVG) and a boundary layer. Application to the control of a separated flow. »

The study fits in one of the priority of the team “Instabilities, Turbulence and Control”, namely the comprehension of the interactions between actuators and a boundary layer, separated or not. Indeed, all works on flow control imply the choice of actuators which will interact with a target flow. Very often, work passes by an important parametric study because of the lack of knowledge of the phenomena brought into play when the actuators interact with the flow. We thus decided to develop an original activity based on the analysis of the interaction between actuators and boundary layers.

Among the various types of possible actuators, we are interested in the Vortex Generators (VG) which, in general, are Generators of Longitudinal Vortices (with the vorticity aligned with the flow). In this family one can distinguish the Mechanical Vortex Generators (vane, solid obstacles of various forms placed in the boundary layer) form Fluidic Vortex Generators. We already carried out many studies on the mechanical Vortex Generators and we now wish to extend our exploration to the Fluidic Vortex Generators, and also to Pulsated Jets.

The use of pulsated jets for flow control is considered as one of the most promising ways for control of the separated flows, and this for several reasons. The first is due to the favourable energy balance: the energy required is smaller for a pulsated jet. The second is due to the existence of two dynamic parameters suitable for closed-loop control, or at least likely to be optimized for a given application: the

speed of the jet and the frequency of pulsation. Moreover the appearance of powerful pulsated micro- jets with MEMS (micro electro-mechanical systems) now allows considering a very good potential of integration in very constrained environments. Lastly, a last advantage offered by this type of actuator is that they do not disturb the flow when the system is not active.

This work, based on an analytical description of the flow, will be primarily experimental. We will use a hydrodynamic tunnel to make a thorough study of the interactions between the jets and the boundary layer. The test facilities will be primarily the PIV 15Hz and the Time-Resolved PIV (TR-PIV with 1kHz sampling frequency for the hydrodynamic flows) and visualization by Laser Induced Fluorescence (LIF). The effect of the JVGs on a separated flow will be also quantified using measurement of drag (global measurement). In parallel, validations out of wind tunnel experiments are envisaged in order to check that the parameters characterizing the efficiency of the actuators can be used on a broad range of Reynolds number. One can also run numerical simulations (CFD) to complement the experimental studies and help in the analysis of the flows.

Through this PhD thesis, our objective is thus double. Initially, we want to find original physical criteria based on hydrodynamical stability and nonlinear evolution of the flow perturbations in the interaction JVG – Boundary layer. In a second time, we want to use them to choose the right dimensions and position of the JVG to control a generic separated flow (smoothly contoured ramp) and thus to propose an effective strategy of control of separated flows.

This work will benefit from strong interactions with a project financed by the ANR (French National Research Agency) and the ADEME (French Association for Energy Savings). This project is directed by the PMMH laboratory with industrial partners like the teams of Research in Aerodynamics of Renault and PSA Peugeot-Citroen. It was proposed in response to the project call “Clean and Economic Vehicles” of the PREDIT in 2007.

The student will benefit from a grant from the French Ministry of Research and Education.

The student should speak English or French.

Short bibliography of the ITC team on the subject

[1] Thiria, B.; Goujon-Durand S., Wesfreid, J.E., “Wake of a cylinder performing rotary oscillations”, Journal of Fluid Mechanics (2006, 560, 123-147,

[2] Thiria, B., Wesfreid, J.E., “Stability properties of forced wakes”, Journal of Fluid Mechanics (2007), 579: 137-161

[3] J. F. Beaudoin, J. L. Aider, O. Cadot, J. E. Wesfreid , “Bluff-body drag reduction by extremum seeking control”, Journal of Fluids and Structures, Vol 22, pp. 973-978, 2006.

[4] J. F. Beaudoin, J. L. Aider, O. Cadot, J. E. Wesfreid , “Drag reduction of a bluff body using adaptive control methods”, Physics of Fluids, 18, 085107, 2006.

[5] T. Duriez, J. L. Aider, J. E. Wesfreid , “Base flow modification by streamwise vortices. Application to the control of separated flow”, ASME Paper, Proceedings of the FEDSM2006 conference, FEDSM2006-98541, 2006

[6] B. Protas and J.E. Wesfreid, “Drag force in a open-loop control of the cylinder wake in the laminar regime”. Physics of Fluids, 14, (2), 810-826, 2002.