Papers by Christophe Airiau
Http Www Theses Fr, 2006
Une couche de melange compressible bidimensionnelle est simulee numeriquement par Simulation Nume... more Une couche de melange compressible bidimensionnelle est simulee numeriquement par Simulation Numerique Directe (DNS) des equations de Navier-Stokes, afin d'en extraire le rayonnement aeroacoustique. Cet ecoulement constitue un modele simplifie de jet, dont on cherche a reduire le bruit emis par application de la theorie du controle optimal. Apres validation de ce modele, les equations adjointes des equations de Navier-Stokes sont numeriquement resolues afin d'etudier dans un premier temps la sensibilite du rayonnement acoustique de la couche de melange a differents forcages. Cette etude nous indique que le bruit emis est particulierement sensible a un forcage a basse frequence applique au niveau de la naissance de la couche. En outre, la sensibilite relative est maximale pour un forcage «massique», sur l'equation de continuite. A partir de ces resultats, nous mettons en place une strategie de controle optimal basee sur la minimisation d'une fonctionnelle-objectif formulee pour reduire le bruit sur une zone cible predeterminee. Le gradient de cette fonctionnelle en fonction du forcage est fourni par la connaissance de l'etat adjoint. L'espace des forcages a explorer est choisi a partir des resultats de l'etude de sensibilite. Un algorithme de gradient conjugue est applique pour chercher le forcage optimal qui minimise la fonctionnelle. Les resultats nous donnent une diminution de celle-ci de l'ordre de 10% pour une zone cible large, et de 75% pour une zone cible reduite. Ces resultats sont compares avec une etude semblable recente, et des interpretations et perspectives sont developpees.
Development of thermal models and DNS + DSMC workflow. * Participates in the analysis of geometri... more Development of thermal models and DNS + DSMC workflow. * Participates in the analysis of geometric effects (elongation, confinement) according to flow regimes. -ISAE: * Participation in WP3, including aspects in ISA condition. * Comparison with the experiments conducted at WP1. * Analysis of geometrical aspects (confinement, elongation). * Participation in diluted approaches -CRITT: * Participation in WP3, * Implementation of IT resources (HW and SW) CFD, heat transfer, DSMC for high fidelity simulations. -HTT: * Cross-evaluation of CFD codes under Hyperloop operating conditions. * Participation in the development of H0 and H1 models * Validations of HF simulations on these models. • Deliverables and Milestone of WP 3 The deliverables are described in table 1.2.
L’Aérodynamique est la branche de la Mécanique des Fluides qui concerne l’écoulement de l’air aut... more L’Aérodynamique est la branche de la Mécanique des Fluides qui concerne l’écoulement de l’air autour d’obstacles ou dans les sillages. L’objectif est d’aboutir, en particulier, à la prédiction des efforts qui vont permettre à un aéronef de réaliser un vol piloté avec une force de portance tout en étant freiné par une force de traînée. Dans un esprit pédagogique, le livre inclut les éléments nécessaires à la compréhension des différentes théories dans tous les régimes de vol depuis les basses vitesses en phase d’atterrissage ou décollage, en passant par les moyennes vitesses en vol de croisière subsonique ou supersonique et jusqu’aux très grandes vitesses hypersoniques lors de la rentrée atmosphérique d’engins spatiaux. Le contenu est issu d’années d’expérience de recherche et d’enseignement cumulées par les auteurs à l’ONERA, l’Université de Toulouse III, dans des écoles d’ingénieurs aéronautiques ou d’autres organismes de formation continue. Ce livre s’adresse aux étudiants de Mast...
The aim of this study is the reduced order modelling based control of highly subsonic cavity flow... more The aim of this study is the reduced order modelling based control of highly subsonic cavity flows. A Direct Numerical Simulation (DNS) of the compressible Navier-Stokes equation at regimes of low subsonic flows has been carried out using an explicit 4th order accurate scheme in ...
HAL (Le Centre pour la Communication Scientifique Directe), Aug 24, 2015
OATAO is an open access repository that collects the work of Toulouse researchers and makes it fr... more OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible.
Journal of Fluid Mechanics, Sep 8, 2022
The flow past a bullet-shaped blunt body moving in a pipe is investigated through global linear s... more The flow past a bullet-shaped blunt body moving in a pipe is investigated through global linear stability analysis (LSA) and direct numerical simulation. A cartography of the bifurcation curves is provided thanks to LSA, covering the range of parameters corresponding to Reynolds number Re = [50-110], confinement ratio a/A = [0.01-0.92] and length-to-diameter ratio L/d = [2-10]. Results show that the first bifurcation is always a steady bifurcation associated to a non-oscillating eigenmode with azimuthal wavenumber m = ±1 leading to a steady state with planar symmetry. For weakly confined cases (a/A < 0.6), the second bifurcation is associated to an oscillating mode with azimuthal wavenumber m = ±1, as in the unconfined case. On the other hand, for the strongly confined case (a/A > 0.8), a destabilization of non-oscillating modes with |m| = 2, 3 and a restabilization of the m = ±1 eigenmodes are observed. The aspect ratio L/d is shown to have a minor influence for weakly confined cases and almost no influence for strongly confined cases. Direct numerical simulation is subsequently used to characterize the nonlinear dynamics. The results confirm the steady bifurcation predicted by LSA with excellent agreement for the threshold Reynolds. For weakly confined cases, the second bifurcation is a Hopf bifurcation leading to a periodic, planar-symmetric state in qualitative accordance with LSA predictions. For more confined cases, more complex dynamics is obtained, including a steady state with |m| = 3 geometry and aperiodic states.
The aim of CFD simulations is to model and compute the ideal performance of a flow under some par... more The aim of CFD simulations is to model and compute the ideal performance of a flow under some particular conditions. A classic approach is to perform simulations with fixed parameters and boundary conditions. However, this is not accurate enough due to the fact that under realistic conditions, some parameters may be uncertain. In recent years, the interest of undertaking the simulations under uncertainty is increasing, but is not yet a common rule and 'incomplete' simulations are still taking place. This procedure could be missing information such as whether mechanical tolerances are influential in dramatic parts of the flow or the relevancy in accurate tunning of turbulence models. Taking this knowledge into consideration, Non-Intrusive Uncertainty Quantification (UQ) has been applied to 3D RANS simulations of an under-expanded jet, in order to understand the impact of input uncertainties. Results show that some regions of the jet plume are very sensitive to a combination of both physical and turbulence model variance. These regions are in fact corresponding to the parts of the jet where screech and shock-cell noise is generated, so this can be an indicator of a relevant impact of uncertainties in jet noise emmission, what can guide to future research and more robust developments in aircraft industry.
HAL (Le Centre pour la Communication Scientifique Directe), Aug 24, 2009
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Cet ouvrage d’exercices est l’ouvrage compagnon du livre de cours "Aérodynamique fondamental... more Cet ouvrage d’exercices est l’ouvrage compagnon du livre de cours "Aérodynamique fondamentale". Issu d’un savoir et d’un savoir-faire très importants, il s’adresse aux étudiants de Master, aux élèves ingénieurs et même à des ingénieurs professionnels qui souhaitent apprendre à résoudre analytiquement ou numériquement des problèmes d’aérodynamique, souvent très concrets. Certains problèmes relativement complexes s’adressent à des doctorants de troisième cycle ou à des chercheurs qui auraient besoin dans leurs activités de recherche de données de référence en aérodynamique. À l’opposé certains exercices sont abordables dès le premier cycle universitaire et en classes préparatoires. Nous espérons aussi que cet ouvrage et les codes fournis pourront être utilisés par des enseignants pour préparer des travaux dirigés, des travaux pratiques, des projets ou des examens. Tout pilote ou passionné d’aéronautique pourra aussi y piocher des informations ou des données. Chaque chapitre est constitué de rappels, d’énoncés et de corrigés détaillés. De nombreux schémas, figures et tableaux permettent de mieux visualiser et de quantifier les données et les résultats associés aux différentes approches théoriques ou numériques. Au travers des quelque 120 exercices et problèmes présentés, cet ouvrage permet d’appliquer et de comprendre les différentes théories dans tous les régimes de vol : les basses vitesses en phase d’atterrissage ou décollage, les moyennes vitesses en vol de croisière subsonique ou supersonique et les très grandes vitesses hypersoniques lors de la rentrée atmosphérique d’engins spatiaux. Une suite logiciel (sous linux et Windows) assez unique, accessible librement sur GitHub, composée de codes dans les langages Python, Fortran, Matlab et Maple, permet de retrouver les solutions de 95 des sujets ou de réaliser ses propres développements ou projets en aérodynamique. Son utilisation exige cependant quelques connaissances en programmation et plus généralement en informatique
Journal of Computational Science
The attenuation power of an acoustic liner is optimized by unsteady compressible flow simulations... more The attenuation power of an acoustic liner is optimized by unsteady compressible flow simulations that model the presence of the liner with a time-domain impedance boundary condition (TDIBC). Two test cases are considered: a one-dimensional impedance tube and a two-dimensional grazing incidence tube. The impact of the liner on the pressure field is tuned through various TDIBC parameters imposed at the boundary where the liner surface is located. Automatic differentiation of the direct numerical simulation (DNS) code yields the gradients of the time-integrated pressure perturbations with respect to the TDIBC parameters. The gradients are subsequently used in an iterative process that minimizes the perturbations at a given location. In both test cases considered, TDIBC parameters are found which are more effective at attenuating perturbation frequencies other than those the initial TDIBC is designed to cancel. Finally, a sensitivity analysis reveals the importance of the choice of the initial TDIBC parameters for finding optimized settings. Our results pave the way to a wider application of the presented procedure in more complex problems with bulk flow motion and larger perturbation amplitudes.
Congress of the International Council of the Aeronautical Sciences, 1994
Shock Waves, 2018
Broadband shock-associated noise (BBSAN) is a particular high frequency noise that is generated i... more Broadband shock-associated noise (BBSAN) is a particular high frequency noise that is generated in imperfectly expanded jets. BBSAN results from the interaction of turbulent structures and the series of expansion and compression waves which appears downstream the convergent nozzle exit of moderately underexpanded jets. This paper focuses on the impact of the pressure waves generated by BBSAN from a large eddy simulation of a non-screeching supersonic round jet in the near-field. The flow is under-expanded and is characterized by a high Reynolds number Re j = 1.25 × 10 6 and a transonic Mach number M j = 1.15. It is shown that BBSAN propagates upstream outside the jet and enters the supersonic region leaving a characteristic pattern in the physical plane. This pattern, also called signature, travels upstream through the shock-cell system with a group velocity between the acoustic speed U c − a ∞ and the sound speed a ∞ in the frequency-wavenumber domain (U c is the convective jet velocity). To investigate these characteristic patterns, the pressure signals in the jet and the near-field are decomposed into waves traveling downstream (p +) and waves traveling upstream (p −). A novel study based on a wavelet technique is finally applied on such signals in order to extract the BBSAN signatures generated by the most energetic events of the supersonic jet.
Physics of Fluids, 2017
This article investigates the structural stability and sensitivity properties of the confined tur... more This article investigates the structural stability and sensitivity properties of the confined turbulent wake behind an elongated D-shaped cylinder of aspect-ratio 10 at Re = 32 000. The stability analysis is performed by linearising the incompressible Navier-Stokes equations around the numerically computed and the experimentally measured mean flows. We found that the vortex-shedding frequency is very well captured by the leading unstable global mode, especially when the additional turbulent diffusion is modelled in the stability equations by means of a frozen eddy-viscosity approach. The sensitivity maps derived from the computed and the measured mean flows are then compared, showing a good qualitative agreement. The careful inspection of their spatial structure highlights that the highest sensitivity is attained not only across the recirculation bubble but also at the body blunt-edge, where tiny pockets of maximum receptivity are found. The impact of the turbulent diffusion on the ...
… Congres Français de …, 2009
L'objectif final de cette étude est d'utiliser un mod`ele réduit construit par POD pour... more L'objectif final de cette étude est d'utiliser un mod`ele réduit construit par POD pour contrôler un écoulement de cavité ouverte en régime compressible. Dans cette communication, nous utiliserons des méthodes de calibration pour améliorer la précision du mod`ele réduit et nous nous ...
Direct and Large-Eddy Simulation X, 2017
A compressible boundary layer flow past a cavity generates noise emission by the Rossiter mechani... more A compressible boundary layer flow past a cavity generates noise emission by the Rossiter mechanism. The sensitivity of any quantity relative to acoustic fluctuation with respect to any perturbations is investigated by Direct Numerical Simulations and their continuous-then-discrete adjoint formulation. Sensitivity functions are the components of the adjoint field. A sensitivity study aims to determine the optimal location of actuators and sensors and the optimal direction of measurement or actuation in a control problem. For a cavity of a length to depth ratio (L/D) of 2 and a Reynolds number of 2982 based on L, we found by Fourier series decomposition some modes which are very similar to the global adjoint instability modes given by the literature. Action in the streamwise momentum equation seems to be a good choice, especially on the wall close to the upstream cavity corner. The sensitivity study is currently implemented in an optimal control algorithm in the goal of reducing nois...
OATAO is an open access repository that collects the work of Toulouse researchers and makes it fr... more OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in:
Understand the underlying physics in a perturbed or controled environment of a jet flow is one of... more Understand the underlying physics in a perturbed or controled environment of a jet flow is one of the key to reduce noise emission in an aircraft turbofan engine. A sensitivity analysis of the pressure instability wave has been performed in a single and double-stream supersonic jet flow. The mean flow is obtained from accurate LES simulation performed at CERFACS (Toulouse) and contains some shock cells and two shear layers which are producing large noise emission. As it has been previously demonstrated, the noise source originates from some instabilities which are amplified through inviscid and viscous mechanisms. The instability are studied in this work using the linear nonlocal stability equations (PSE) under an inviscid formulation. To investigate sensitivity, their adjoint counterpart called ’APSE’ have been developed following the previous Airiau’s works on the laminar boundary layer control(2003). Sensitivities of the energy or acoustic energy of the perturbation are solved wi...
International Journal of Mechanical Sciences, 2021
Advances in Water Resources, 2020
Porous media Homogeniz.adon Adjoint theory Carreau fluids Pseudo-plastic fluids exhibit a non-Jin... more Porous media Homogeniz.adon Adjoint theory Carreau fluids Pseudo-plastic fluids exhibit a non-Jinear stress-strain relationship which can provoke large, localized viscosity gradients. For the fl ow of such fl uids in porous media the consequence is a strong varia b ility of the effective permeability with poroeity, angle of the macroscopic pressure gradien t, and meological parameters of the fluid. Such a variability is investigated on the basis of ad j oint homogenization theory for a Carreau fluid in an idealized porous medium geometty, highlighting differences with respect to the Newtonian case. It is shown in particular that the more we de part from Newtonian conditions, the more the (often used) hypothesis of an effective viscosity in Darc y' s law is a poor approximation, for the effective permeability tensor becomes strongly anisotropie.
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Papers by Christophe Airiau