Publications de Edouard Boujo | EPFL Graph Search

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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 ...

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 ...

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 ...

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 ...

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 ...

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 ...

Linear optimal gains

G_{opt}(\omega)

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 ...

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 ...

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 ...

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. ...

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 ...

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 ...

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 ...

Three-dimensional control is considered in the flow past a backward-facing step (BFS). The BFS flow at Reynolds number Re = 500 (defined with the step height and the maximum inlet velocity) is two-dimensional and linearly stable but increasingly receptive ...

The primary bifurcation of the flow past three-dimensional axisymmetric bodies is investigated. We show that the azimuthal vorticity generated at the body surface is at the root of the instability, and that the mechanism proposed by Magnaudet & Mougin (200 ...

This study assesses the ability of a sensitivity-based, span-wise homogeneous control velocity distributed at the surface of a circular cylinder to cut down the cost of reducing drag by more classical techniques, e.g., base bleed and lateral suction. At Re ...

Linear optimal gains are computed for the subcritical two-dimensional separated boundary-layer flow past a bump. Very large optimal gain values are found, making it possible for small-amplitude noise to be strongly amplified and to destabilize the flow. Th ...

The question of optimal spanwise-periodic modification for the stabilisation of spanwise-invariant flows is addressed. A second-order sensitivity analysis is conducted for the linear temporal stability of parallel flows U-0 subject to small-amplitude spanw ...

Edouard Boujo

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

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

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

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

Open-loop control of a separated boundary layer

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

Open-loop control of a separated boundary layer

Adjoint-aided Homogenisation for Flows Through Heterogeneous Membranes

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

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

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

Liquid film instability of an internally coated horizontal tube

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

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

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

Optimal spanwise-periodic control for recirculation length in a backward-facing step flow

On the symmetry-breaking instability of the flow past axisymmetric bluff bodies

Revisiting the drag reduction problem using adjoint-based distributed forcing of laminar and turbulent flows over a circular cylinder

Open-loop control of noise amplification in separated boundary layers

Second-order sensitivity of parallel shear flows and optimal spanwise-periodic flow modifications