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Edouard Boujo

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Related publications (31)

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Second-order sensitivity in the cylinder wake: Optimal spanwise-periodic wall actuation and wall deformation

François Gallaire, Edouard Boujo, Andrea Fani

Two-dimensional (2D) flows can be controlled efficiently using spanwise "waviness," i.e., a control (e.g., wall blowing and suction or wall deformation) that is periodic in the spanwise direction. This study tackles the global linear stability of 2D flows ...

AMER PHYSICAL SOC2019

Sensitivity and open-loop control of stochastic response in a noise amplifier flow: the backward-facing step

François Gallaire, Edouard Boujo

The two-dimensional backward-facing step flow is a canonical example of noise amplifier flow: global linear stability analysis predicts that it is stable, but perturbations can undergo large amplification in space and time as a result of non-normal effects ...

Cambridge University Press2015

An adjoint-based approach to the optimal control of separated flows

Edouard Boujo

Flow separation is relevant to many industrial applications, since it is detrimental to the aerodynamic performance of vehicles, induces vibrations in mechanical structures, but can also contribute to improve mixing in combustion devices. In this thesis, t ...

EPFL2014

Three-dimensional nonlinear dynamics of a thin liquid film on a spinning ellipsoid

Edouard Boujo

The present work investigates the three-dimensional flow of a thin liquid film distributed on the outer surface of an ellipsoid, rotating around the vertical axis at constant angular velocity. The lubrication approximation expressing the evolution of the f ...

2023

Sensitivity of aerodynamic forces in laminar and turbulent flow past a square cylinder

François Gallaire, Edouard Boujo, Philippe Meliga

We use adjoint-based gradients to analyze the sensitivity of the drag force on a square cylinder. At Re = 40, the flow settles down to a steady state. The quantity of interest in the adjoint formulation is the steady asymptotic value of drag reached after ...

Amer Inst Physics2014

Open-loop control of a separated boundary layer

François Gallaire, Edouard Boujo

Linear optimal gains

G_opt(\omega)

are computed for the separated boundary-layer flow past a two-dimensional bump in the subcritical regime. Very large values are found, making it possible for small-amplitude noise to be strongly amplified and to destabi ...

Cépaduès Editions2013

Noise-induced transitions past the onset of a steady symmetry-breaking bifurcation: The case of the sudden expansion

François Gallaire, Edouard Boujo, Yves-Marie François Ducimetière

We consider fluid flows, governed by the Navier-Stokes equations, subject to a steady symmetry-breaking bifurcation and forced by a weak noise acting on a slow timescale. By generalizing the multiple-scale weakly nonlinear expansion technique employed in t ...

2024

Homogenization-based design of microstructured membranes: wake flows past permeable shells

François Gallaire, Edouard Boujo, Pier Giuseppe Ledda, Giuseppe Antonio Zampogna

A formal framework to characterize and control/optimize the flow past permeable membranes by means of a homogenization approach is proposed and applied to the wake flow past a permeable cylindrical shell. From a macroscopic viewpoint, a Navier-like effecti ...

Cambridge University Press2021

Open-loop control of a separated boundary layer

François Gallaire, Edouard Boujo

Linear optimal gains

G_{opt}(\omega)

Elsevier France-Editions Scientifiques Medicales Elsevier2014

Adjoint-aided Homogenisation for Flows Through Heterogeneous Membranes

François Gallaire, Edouard Boujo, Kevin Wittkowski

Porous membranes, like nets or filters, are thin structures that allow fluid to flow through their pores. Homogenisation can be used to rigorously link the flow velocity with the stresses on the membrane via several coefficients (e.g. permeability and slip ...

CAMBRIDGE UNIV PRESS2025

Numerical simulation and sensitivity analysis of a low-Reynolds-number flow around a square cylinder controlled using plasma actuators

François Gallaire, Edouard Boujo, Philippe Meliga

Flow around a square cylinder controlled using plasma actuators (PAs) is numerically investigated by direct numerical simulation in order to clarify the most effective location of actuator installation and to elucidate the mechanism of control effect. The ...

Amer Physical Soc2017

A general model for spin coating on a non-axisymmetric curved substrate

Edouard Boujo

We derive a generalised asymptotic model for the flow of a thin fluid film over an arbitrarily parameterised non-axisymmetric curved substrate surface based on the lubrication approximation. In addition to surface tension, gravity and centrifugal force, ou ...

Cambridge University Press2024

Manipulating flow separation: sensitivity of stagnation points, separatrix angles and recirculation area to steady actuation

François Gallaire, Edouard Boujo

A variational technique is used to derive analytical expressions for the sensitivity of several topological indicators of flow separation to steady actuation. Considering the boundary layer flow above a wall-mounted bump, the six following representative q ...

Royal Soc2014

Weakly nonlinear evolution of stochastically driven non-normal systems

François Gallaire, Edouard Boujo, Yves-Marie François Ducimetière

We consider nonlinear dynamical systems driven by stochastic forcing. It has been largely evidenced in the literature that the linear response of non-normal systems (e.g. fluid flows) may exhibit a large variance amplification, even in a linearly stable re ...

Cambridge University Press2022

Second-order adjoint-based sensitivity for hydrodynamic stability and control

Edouard Boujo

Adjoint-based sensitivity analysis is routinely used today to assess efficiently the effect of open-loop control on the linear stability properties of unstable flows. Sensitivity maps identify regions where small-amplitude control is the most effective, i. ...

Cambridge University Press2021

Liquid film instability of an internally coated horizontal tube

François Gallaire, Edouard Boujo, Yves-Marie François Ducimetière, Shahab Eghbali

We study numerically and theoretically the gravity-driven flow of a viscous liquid film coating the inner side of a horizontal cylindrical tube and surrounding a shear-free dynamically inert gaseous core. The liquid-gas interface is prone to the Rayleigh-P ...

AMER PHYSICAL SOC2023

A self-consistent formulation for the sensitivity analysis of finite-amplitude vortex shedding in the cylinder wake

François Gallaire, Edouard Boujo, Philippe Meliga

We use the adjoint method to compute sensitivity maps for the limit-cycle frequency and amplitude of the Benard von Karmzin vortex street in the wake of a circular cylinder. rfhe sensitivity, analysis is performed in the frame of the semi-linear self consi ...

Cambridge University Press2016

From thin plates to Ahmed bodies: linear and weakly nonlinear stability of rectangular prisms

Edouard Boujo, Giuseppe Antonio Zampogna

We study the stability of laminar wakes past three-dimensional rectangular prisms. The width-to-height ratio is set to W/H = 1.2, while the length-to-height ratio 1/6 < L/H < 3 covers a wide range of geometries from thin plates to elongated Ahmed bodies. F ...

Cambridge University Press2023

Controlled reattachment in separated flows: a variational approach to recirculation length reduction

François Gallaire, Edouard Boujo

A variational technique is used to derive analytical expressions for the sensitivity of recirculation length to steady forcing in separated flows. Linear sensitivity analysis is applied to the two-dimensional steady flow past a circular cylinder for Reynol ...

Cambridge University Press2014

Whirling instability of an eccentric coated fibre

François Gallaire, Edouard Boujo, Ludovic Pierre Gustave Keiser, Shahab Eghbali

We study a gravity-driven viscous flow coating a vertical cylindrical fibre. The destabilisation of a draining liquid column into a downward moving train of beads has been linked to the conjunction of the Rayleigh-Plateau and Kapitza instabilities in the l ...

Cambridge University Press2022