Séminaire FTC : Des anneaux tourbillonnaires qui font du yoyo – Julie Albagnac

Résumé:

Les anneaux tourbillonnaires (AT) sont des structures toroidales de vorticité qui se forment naturellement dans les sillages d’objets ou lors d’éjection de fluide (jet impulsif). Ces tourbillons dominent ainsi la dynamique de nombreux écoulements et sont observés dans des environnements variés. De part leur topologie, les AT ont la propriété de se propager dès lors qu’ils sont créés. Ils transportent alors le fluide qui les compose le long de leur trajectoire. Cela leur confère un pouvoir d’agitation et de mélange dans des zones éloignées de leur lieu de génération. A l’occasion de ce séminaire je présenterai des études que nous avons menées à l’IMFT sur des AT évoluant dans des milieux (i) stratifiés en densité et (ii) rhéofluidifiants viscoélastiques.

(i) De nombreux écoulements sont stratifiés en densité. Par exemple, l’océan et l’atmosphère sont stratifiés en salinité et/ou en température et donc en densité. Lorsqu’un AT pénètre une stratification, les isopycnes se déforment et de la vorticité secondaire barocline est générée. La vorticité primaire, transportée par l’AT, va alors se réorganiser avec la vorticité secondaire. Concernant la dynamique du milieu support, des ondes de gravité sont forcées par l’impact de l’AT et il résulte des interactions fortes entre les ondes générées et la structure tourbillonnaire propagative.

(ii) De nombreux écoulements mettent en jeu des fluides ayant une rhéologie non-newtonienne. On peut citer par exemple le manteau terrestre et la plupart des fluides utilisés dans l’industrie agroalimentaire. Nous nous sommes intéressés à la dynamique singulière d’un AT dans un fluide viscoélastique. En particulier, nous essayons de comprendre les mécanismes menant au « rebond » de la structure tourbillonnaire en milieu infini, i.e., sans présence de paroi solide.

 

Séminaire FTC : Length of the establishment of roll waves in free-surface flows – Guilherme Fiorot

Résumé: Free-surface flows are subdued to hydrodynamic instabilities, one of them observed as a coherent structure propagating at the interface between the viscous fluid flow and air named roll waves. Those instabilities develop from spatial and/or time disturbances, reaching a stationary regime downstream. Then, one important feature to predict the evolution of such a phenomenon is the length required for disturbances to travel before reaching their stationary form. The present work brings a theoretical and numerical analysis of such length required for roll waves to become stationary in a free-surface laminar flow of a Newtonian fluid. Two types of stability analysis are brought to verify flow stability and obtain parameters for wave growth rate in a Saint-Venant-like system. Then, numerical simulations are performed of the free-surface laminar transient flow of glycerin. The Navier-Stokes equations were solved using the finite volumes method, Euler schemes and PIMPLE, and the VoF technique to solve the interface. Boundary conditions were specified to obtain a steady and uniform regime given a Froude number. Then, a sinusoidal perturbation with controllable properties was applied to the inlet velocity. From the numerical results, the spatial development of the roll waves was evaluated, focusing on the establishment length as a function of the Froude number and the perturbation amplitude. The analyses performed allowed the verification of the influence of the flow’s hydraulic regime over the establishment length, and it was possible to obtain a new equation as a function of the perturbation amplitude.

Séminaire FTC : Stability of foam films and bubbles stability

Emmanuelle Rio

The stability of soapy objects such as films, bubbles and foams has been studied widely because of the numerous applications concerning food industry, climate prediction or artistic utilization of giant bubbles.

It has been demonstrated that their stability is primarily affected by the thinning dynamics of the thin soap films. The drainage dynamics, which is the capillary or gravity driven flow in the liquid film has been widely investigated [1]. However, more recently, researchers also became interested in the influence of evaporation on this thinning dynamics [2,3].

In this seminar, I will show that, to describe bubble stability, evaporation must be taken into account as soon as the films are thin enough [4]. We will see that the bubble lifetime can be predicted by taking into account both the drainage and the evaporation to describe the thinning dynamics [2] and that this is all the more important concerning the stability of giant soap films. I will also esquisse some hypothesis concerning the influence of physical-chemistry on the film thinning and evaporation. This last result comes from a collaboration with bubbles artists, in which we developed a scientific approach to rationalize their best recipes.

[1] H. Lhuissier and E. Villermaux, J. Fluid Mech., 2012, 696, 5-44.
[2] J. Miguet, M. Pasquet, F. Rouyer, Y. Fang and E. Rio, Soft Matter, 2020, 16, 1082–1090.
[3] S. Poulain and L. Bourouiba, Phys. Rev. Lett., 2018, 121, 204502.
[3] A. Roux, A. Duchesne, M. Baudoin, Physical Review Fluids, 7(1), L011601,2022.
[4] Champougny, L., Miguet, J., Henaff, R., Restagno, F., Boulogne, F., Rio, E., Influence of evaporation on soap film rupture. Langmuir, 34(10), 3221-3227, 2018.

Séminaire FTC : Microgravity E-FIELD Flames on the ISS and Gas Hydrates for Combustion Research – Alice Yu-Chien

Yu-Chien (Alice)

Associate Project Scientist
Director of Lasers, Flames & Aerosols
UNIVERSITY OF CALIFORNIA
Irvine, CA USA

ABSTRACT:

Electric Field Effects on Laminar Diffusion Flames (E-FIELD Flames) is one of the Advanced Combustion via Microgravity Experiments (ACME) of the National Aeronautics and Space Administration (NASA). The E-FIELD Flames experiment studies a hydrocarbon flame jet to determine how an electric field leads to an electric body force and a resultant ion-driven wind when the normal 1-g buoyant force is not participating in the process. The E-FIELD Flames experiment was boarded onto the international space station on March 14th, 2018 (\pi day) and was accomplished in November of the same year. The goal of the study is to expose the physico-thermo-chemical processes when an electric field is applied without gravitational effect. The results show that the flame is most compact at saturation while the measured voltage to current (VCC) curve demonstrates parabolic behavior after saturation which differs from observations in 1 g on Earth. The second part of the talk will briefly survey the current research developing in the Keck Foundation Deep Ocean Power Science Laboratory (DOPSL) and the Lasers, Flames & Aerosols Research Group (LFA) at UCI, including high pressure combustion experiments, water addition combustion, methane hydrate combustion, carbon dioxide hydrate fire extinguishment, and hydrogen/methane blending for optical diagnostics measurement.

Séminaire FTC: Dynamics and Bifurcations of Swirling Jets – Chris Douglas

ABSTRACT:
Among the family of canonical shear flows, swirling jets represent a remarkable genus with widespread practical and scientific interest. Despite this interest, the swirling jet parameter space has proven difficult to repeatably characterize via experiments and conventional time-marching computations. Even in the laminar regime, swirling jets host a suite of rich physics related to the complex interplay among axial and azimuthal shear layers, centrifugal forces, propagating inertial waves, and various geometric effects. These myriad interactions lead to pronounced nonlinear effects including, in particular, multivalued relationships among distinct steady and unsteady states. In this seminar, I will summarize results from three recent reports that rigorously characterize the dynamics and bifurcations of circular and annular laminar swirling jets using branch continuation methods. This approach allows a concrete exposition of the swirling jet’s underlying state space, which can then be related back to its behavior in the physical space. The chosen examples offer insight into several important dynamical features of swirling jets including central jet/wall jet transitions and precessing vortex core (PVC) oscillations.

BIO:
Christopher Douglas is currently a Marie Sklodowska–Curie postdoctoral fellow at the Hydrodynamics Laboratory (LadHyX) at Ecole Polytechnique in France. Chris’ postdoctoral research, supervised by Lutz Lesshafft (l’X) and Wolfgang Polifke (TUM) investigates the response of hydrogen jet flames to generic perturbations using the framework of resolvent analysis. Prior to his postdoc, Chris completed his PhD in Mechanical Engineering at Georgia Tech in May 2021 under the supervision of Tim Lieuwen, where his doctoral studies focused on the dynamics of swirling jets and jet flames.

 

Séminaire FTC: Modeling and controlling turbulent flows through deep learning – Ricardo Vinuesa

Abstract:

The advent of new powerful deep neural networks (DNNs) has fostered their application in a wide range of research areas, including more recently in fluid mechanics. In this presentation, we will cover some of the fundamentals of deep learning applied to computational fluid dynamics (CFD). Furthermore, we explore the capabilities of DNNs to perform various predictions in turbulent flows: we will use convolutional neural networks (CNNs) for non-intrusive sensing, i.e. to predict the flow in a turbulent open channel based on quantities measured at the wall. We show that it is possible to obtain very good flow predictions, outperforming traditional linear models, and we showcase the potential of transfer learning between friction Reynolds numbers of 180 and 550. We also discuss other modelling methods based on autoencoders (AEs) and generative adversarial networks (GANs), and we present results of deep-reinforcement-learning-based flow control.

Bio:
Dr. Ricardo Vinuesa is an Associate Professor at the Department of Engineering Mechanics, at KTH Royal Institute of Technology in Stockholm. He is also a Researcher at the KTH Climate Action Centre and Vice Director of the KTH Digitalization Platform. He studied Mechanical Engineering at the Polytechnic University of Valencia (Spain), and he received his PhD in Mechanical and Aerospace Engineering from the Illinois Institute of Technology in Chicago. His research combines numerical simulations and data-driven methods to understand and model complex wall-bounded turbulent flows, such as the boundary layers developing around wings and urban environments. Dr. Vinuesa has received, among others, an ERC Consolidator Grant and the Göran Gustafsson Award for Young Researchers.

Workshop Méthodes Frontières Immergées en Nouvelle-Aquitaine

Le Groupe Transversal Simulation Numérique et Modélisation (GT SiMoN) a pour ambition d’aider les chercheurs de l’institut Pprime Pprime et du Laboratoire de Mathématiques et Applications à développer des synergies sur des activités de recherche en lien avec la simulation numérique et le calcul scientifique afin d’une part d’aider dans les axes scientifiques des laboratoires et d’autre part de permettre l’éclosion de nouvelles thématiques. Cette année, le GT-SiMoN organise à Poitiers un évènement fédérateur au niveau régional.

Dans la continuité des journées Calcul et Simulation en Nouvelle Aquitaine organisées à Arcachon en décembre 2021, nous organisons les 4 et 5 Octobre 2022 à Poitiers un Workshop sur une thématique commune à un nombre important de chercheurs de l’institut Pprime, du LMA et au niveau régional, à savoir les méthodes de frontières immergées (IBM). Le but de ces deux journées est de poursuivre les échanges scientifiques avec les collègues de la région afin de déboucher sur deux ou trois propositions de stages Master2 que nous financerons pour l’année universitaire 2022/2023.

Ce Workshop sera divisé en une journée dédiée aux IBM pour écoulements incompressibles et l’autre aux écoulements compressibles. Ces journées seront elles-mêmes divisées en deux moments, la matinée dédiée aux présentations et l’après-midi à des tours de table/discussions sur les sujets vues le matin. Les matinées débuteront par deux exposés d’experts suivis d’exposés de jeunes docteurs ou doctorants confirmés, qui présenteront leurs travaux sur ces méthodes.

Comité d’organisation :

Nicolas James
Philippe Parnaudeau

Comité scientifique :

Héloïse Beaugendre
Julien Dambrine
Eric Lamballais
Thomas Milcent
Arnaud Mura

 

Site: https://jibmna.conference.univ-poitiers.fr/index.php

Séminaire FTC: Freezing contact line – Thomas Séon

Freezing contact line

Thomas Séon
Institut ∂’Alembert, CNRS, Sorbonne Université, Paris, France

Ice accretion on airplane, wire or roadway, formation of ice fall, ice stalactite, frozen river or aufeis, are a few examples of ice structures formed by the solidification of capillary flows (drop, rivulet, film). Among the many scientific questions that remain open to understand these problems, the effect of freezing on the contact line motion is undoubtedly one of the most important and mysterious. In this talk, we experimentally investigate three situations where advancing and receding contact line is coupled to freezing : capillary and inertial spreading of a water droplet on a cold substrate and water film dewetting on its own ice. These configurations allow us to propose the main mechanisms that explain the arrest of a contact line due to solidification and to tackle the intricate problem of the wetting of water on ice.

Séminaire FTC: Application of Passive and Active Flow Control to a Supersonic Multistream Rectangular Nozzle – Mark Glauser, PhD

ABSTRACT

Passive and active flow control techniques are applied experimentally to examine different aspects of a supersonic multistream rectangular nozzle representing a modern airframe-integrated variable cycle engine. The flow is comprised of a core stream (M = 1.6) and bypass (M = 1.0) that merge behind a splitter plate and exit through a Single Expansion Ramp Nozzle (SERN) onto an aft-deck. Previous efforts for the nominal nozzle configuration have shown that an instability initiated at the splitter plate trailing edge (SPTE) influences the effectiveness of the third stream as a barrier for the aft-deck and persists through the entire domain due to its reaction with the shock train. To address this, the passive flow control was implemented by introducing sinusoidal spanwise modifications along the splitter plate edge. The SPTE was identified as the highest region of sensitivity via LES. Results on different spanwise wavenumbers indicate reduction of the dominating tone with increasing wavenumber. Additionally, the sinusoidal trailing edge induces streamwise vorticity, which enhances mixing between the two streams and breaks up the shed structures seen previously. A wavenumber corresponding to one simulated was tested experimentally via the use of simultaneous nearfield pressure and velocity in conjunction with far field acoustics. Fairfield acoustic measurements have confirmed the diminishment of the tone for the wavy SPTE. PIV and velocity profiles for mean fields revealed higher plume vectoring for the nominal aft-deck. The shear layers and the region along the aft-deck surface displayed significant enhancement of velocity variability through low order statistics. As a result of this increase, the POD modes were reordered for the wavy SPTE. Wavy modes had smaller spatial structures presented in lower modes, with increased energy content when compared to the same modes in the nominal flow.   Current active control experiments involve replacing the wavy splitter with a bank of jets spaced at the same wavelength.   This allows us to explore if similar results to the wavy splitter can be obtained with the nominal splitter and the bank of jets.

Mark Glauser, PhD

Professor of Mechanical and Aerospace Engineering 

College of Engineering and Computer Science 

Professor of Physics,  College of Arts and Sciences 

Syracuse University 

263 Link Hall

Syracuse, New York 13244

Fellow: AIAA, ASME, APS, Institute of Physics (UK)

Séminaire FTC: L’inégalité diurne dans la baie du Mont-Saint-Michel : impact sur la dynamique des ressauts de marée et sur les archives sédimentaires

Lucille Furgerot

Le projet ANR Mascaret (2011 à 2015) a permis, entre autres, d’instrumenter le mascaret dans la baie du Mont-Saint-Michel. Cette baie hypertidal très étudiée dans sa partie externe pour des problématiques d’envasement reste peu connue dans sa partie interne. La dernière campagne de terrain menée dans l’estuaire interne de la Sée sur un cycle de marée semi-mensuel (14 jours), a fourni un set de données complet sur l’évolution des ressauts de marées en fonction du marnage et de leur impact sur le transport sédimentaire. Le couplage de ces données avec quelques observations récentes d’enregistrements sédimentaires met en évidence une amplification de l’inégalité diurne pouvant altérer la lecture des archives sédimentaires.

Légende :

a.Localisation du site d’étude (rectangle rouge); b.Lecture d’une coupe sédimentaire de berge. Chaque doublet (d1 à d9) représente le dépôt sédimentaire lors d’une seule phase de flot (1 doublet = 1 marée) ; c.Evolution de la hauteur d’eau (en rouge) et de la concentration en matières en suspension sur le fond (points noirs) et à 40 cm au-dessus du fond (points bleus), pour 4 marées successives. a.B. = above the bottom; TR = marnage externe mesuré à St Malo.