Search

The authors regret for the mistake but Fig. 3 in the published article is not the correct one. The correct figure is here below together with its caption: The authors would like to apologise for any inconvenience caused., SCOPUS: er.j, info:eu-repo/semantics/published

Cryogenic sloshing is of primary importance in aerospace propulsion since it can affect the dynamic stability and the propellant management during each phase of spacecraft missions. We show in this work, for the first time, that cryogenic sloshing can be investigated by means of tracer-based laser techniques, such as Particle Image Velocimetry (PIV), to obtain the liquid/gas interface and the bulk velocity both in the unsteady and steady regime. The fluid heating due to the laser interaction with the tracer particles and the possible effect on the particle-fluid slip velocity is evaluated. An experimental campaign is conducted, and both the liquid/gas interface position and the velocity maps of the bulk are obtained in time-resolved conditions. Finally, the logarithmic damping at the liquid/gas interface and in the bulk are evaluated and compared with satisfactory results to the models available in the literature., SCOPUS: ar.j, info:eu-repo/semantics/published

The measurement of fluid velocity in the vicinity of wavy interfaces by means of Particle Image Velocimetry (PIV) still constitutes a challenge. Besides the experimental complexities such as appropriate seeding, reflections due to gradients in refractive indices, aberrations, etc. also the image processing phase constitutes a critical component. Ignoring bias errors introduced by laser reflections near the interface, strong velocity gradients are typically encountered near the curved liquid/gas interface and are detrimental to the common cross-correlation analysis. These effects are exacerbated by the use of traditional rectangular static cross-correlation windows. Moreover, dynamic boundaries suffer from a certain loss in reliability due to the difference in number of particles located in a specific physical region between the two frames. In this paper we present an improved algorithm enhancing the accuracy of the velocity vector detection in dynamic wavy flows. This algorithm divides the fluid domain in subregions (i.e. bulk, intermediate, vicinity and interface) and applies to each region different features (such as image patching, window relocation and forward difference finite schemes) and ad hoc predictors. Its assessment is performed on the basis of synthetic images, which reproduce a wavy motion similar to the one encountered when fluid in a cylindrical reservoir undergoes sloshing. When juxtaposed with a standard PIV code, numerical errors are shown to strongly diminish while improving the spatial resolution approaching the interface. The algorithm is finally applied to experimental PIV images of water sloshing in a cylindrical reservoir to provide more reliable results at the interface, contrary to standard PIV codes., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

The motion of the free liquid surface inside a reservoir is called sloshing. Itis of large interest in different industrial fields such as satellite and spacecrafttrajectory control, automotive industry, nuclear engineering, buildingdesign, etc. The framework of propellant management on spacecraft is ofmain interest for this PhD thesis, even if its outcome can be applied to manyother fields concerned by sloshing.Being able to understand the behavior of the fluid in a reservoir subjectedto extreme environmental conditions means being able to predict its positionand topology inside the tank, for a given external and gravitationalacceleration and a determined thermodynamic condition. The predictionand control of this motion is far from being understood due to the differentparameters that play a role in the dynamic system such as the geometryof the container, the type of external excitation (shape, frequency contentand amplitude), the level of the liquid and finally the kind of liquid. In particular,the design of propulsion systems are affected by this phenomenon,still hampered by the unavailability of validated CFD models. Moreover theexisting experimental studies are mainly based on intrusive and local singlepoint measurement techniques, which give no information on the behaviorof the 3D liquid interface and on the velocity field inside the liquid phase.The main goal of this project has been to extend the experimental approachof liquid sloshing investigation in space propulsion, studying, developing andimproving non-intrusive measurement techniques for free surface behaviorand velocity characterization in the liquid phase. In particular, the free surfacebehavior have been studied by means of Laser Detection and Recordingtechnique (LeDaR), retrieving the profile of the interface over a line, andReference Image Topography technique (RIT), capturing the instantaneous3D interface shape. In addition, Particle Image Velocimetry (PIV) have beenused to measure the 2D velocity, Doctorat en Sciences de l'ingénieur et technologie, La thèse a également été publiée par le von Karman Institute for Fluid Dynamics, sous l'ISBN 978-2-87516-140-6, info:eu-repo/semantics/nonPublished

The Belgian nuclear research institute (SCK•CEN) is developing MYRRHA. MYRRHA is a flexible fastspectrum research reactor ,conceived as an accelerator driven system (ADS). It is designed to operate in sub-critical and critical modes, with a proton accelerator producing the neutron source by spallation. Theconfiguration of the primary loop is pool-type: the primary coolant and all the primary system components (coreand heat exchangers) are contained within the reactor vessel, while the secondary fluid is circulating in the heatexchangers. The primary coolant is Lead Bismuth Eutectic (LBE). The recent nuclear disaster of Fukushima in2011 changed the requirements for the design of new reactors, which should include the possibility to removethe residual decay heat through passive primary and secondary systems, i.e. natural convection (NC).Verifying that sufficient mass flow takes place between the core and the heat exchanger in passive decay heatremoval conditions (core power=11MW) is necessary to fulfill the safety requirement. Analyzing the naturalconvection flow before building the reactor is therefore the primary objective of this work. Furthermore, it is ofinterest to understand which factors contribute to enhance or decrease the primary coolant mass flow. Inparticular, stratification and pressure drops in the primary hydraulic loop are expected to play important roles.The secondary objective of the study was therefore to verify the influence of the loop geometry and of theplenum on the mass flow.The methodology chosen to address the primary objective of the study consisted in measuring the quantities ofinterest in a 1:5 scaled water model (MYRRHABELLE) of the reactor. In particular the simultaneousmeasurement of mass flow, velocity field and temperature in natural convection working conditions is requiredto fulfill the first objective. Facilities of increasing size and complexity were used to develop experimentalmethodology and techniques before carrying out the e, Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

An experimental technique is introduced for measuring the contact angle of small colloidal particles at planar fluid interfaces. The presented light scattering-based method relies on performing two spectral transmittance measurements: one on a particle monolayer standing at the fluid interface and the other on a dispersion of the same particles in a homogeneous medium. The observed shift between the two transmitted spectra is explained in terms of the phase shift parameter, which is then used to determine the particle position relative to the interface and hence the contact angle. The applicability of the technique is demonstrated through simulations and experiments., SCOPUS: ar.j, info:eu-repo/semantics/published

The present paper is dedicated to the assessment of the Light Extinction Spectroscopy (LES) technique for the characterization of submicron particles. This technique allows the measurement of the size distribution of a particle cloud starting from its Ultraviolet Near-Infrared light transmittance spectrum and is applicable in the size range going from few nanometers up to dozens of microns. The main goal of the present work is to validate the technique experimentally, using as reference both an established commercially available instrument and calibrated spherical particles. In particular, the experimental validation of the LES technique is presented for potassium chloride (KCl) and polystyrene (PS) submicron particles. In the case of KCl particles, the validation is obtained using simultaneously a Scanning Mobility Particle Sizer (SMPS), while for PS particles calibrated spheres are used. It is demonstrated that both for monodisperse and polydisperse particle size distributions, the LES technique is in a satisfactory quantitative agreement in terms of the particle size distribution function., SCOPUS: ar.j, info:eu-repo/semantics/published

The purpose of the present research is to develop and apply an experi- mental technique for measuring the size of nanoparticles and nanodroplets in a flow environment. The developed non-intrusive, optical method is called Light Extinction Spectroscopy (LES) and it allows to determine the size of particles from measuring their light transmission spectrum on the Ultraviolet-Near-Infrared range. The most crucial part of the develop- ment work is to obtain a reliable data processing method, which is based on the regularized solution of an ill-conditioned inverse problem. The de- veloped method is first tested using synthetic data, which allows to deter- mine the measurement range and also the measurement errors caused by various sources. This is followed by performing laboratory experiments for validating the LES technique. Validation measurements using calibrated particles and a reference instrument shows that sizing errors are in the order of 5-10%. Afterwards, the technique is applied for characterizing the Brownian coagulation process of nanodroplets, where the growth rate of droplets is successfully measured and is found to agree with theoreti- cal expectations. Next, the LES technique is applied to coagulating solid particles, where the growth rate of these complex non-spherical objects is retrieved. Finally, a particle monolayer is deposited on an air-water inter- face and it is shown that the LES technique can retrieve the particle-water contact angle, which allows the characterization of nanoparticle wettabil- ity and the study of the related interesting physical phenomena., Doctorat en Sciences de l'ingénieur et technologie, info:eu-repo/semantics/nonPublished

L’étude du ballottement des liquides dans leur récipient est fondamentale dans plusieurs domaines, spécialement pour la conception des dispositifs de gestion du carburant aérospatial. D’ailleurs, la réponse dynamique aux mouvements d’un liquide dans un réservoir peut influencer façon significative la trajectoire du véhicule. Dans cette étude, le ballottement asymétrique de l’eau dans un cylindre circulaire soumis à des excitations sinusoïdales externes est étudié expérimentalement par vélocimétrie par images de particules fluorescentes (f-PIV). L’acquisition des images PIV est réalisée en phase avec un instant choisi de l’excitation externe. Les paramètres utilisés pour caractériser le ballottement sont la taille du cylindre, la hauteur du liquide et la fréquence du mouvement externe appliquée. La théorie relative à la géométrie utilisée est présentée pour mieux comprendre les résultats concernant les champs de vitesse et le déplacement de l’interface. Un code a été développé pour détecter l’interface gaz/liquide, directement sur les images PIV, afin de délimiter à l’aide d’un masque le domaine dans lequel déterminer le champ de vitesse par corrélation PIV. Deux traitements différents d’images PIV sont testés pour comparaison :la méthode classique de traitement PIV et un traitement combiné PIV+PTV. Enfin, quelques exemples des informations récoltées par ce type de mesure appliquée au cas du ballottement sont présentés., info:eu-repo/semantics/published

The asymmetric water sloshing in a partially filled circular cylindrical container subjected to horizontal harmonic excitations is investigated. The understanding of this phenomenon is fundamental for the design of propellant management devices. The dynamic response of the moving liquid inside the tank can dramatically influence the trajectory of vehicles. The asymmetric sloshing is controlled by the liquid depth, forcing frequency and amplitude. Above all, the behavior of the free liquid surface is of major interest. The analytical and equivalent mechanical models of the simplified undamped problem are introduced. Fluorescent Particle Image Velocimetry is used to investigate the velocity field in the liquid phase. The f-PIV is phase locked with a selected phase of the external excitation in order to provide statistical data. An image processing algorithm is developed to detect the free surface and to properly define the fluid field of interests. The commercial algorithms of PIV and the combined PIV+PTV of DaVis8 are compared. Some examples of information that can be extracted from the PIV phase locked results for the sloshing phenomenon are presented., info:eu-repo/semantics/published

info:eu-repo/semantics/nonPublished