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Papers by Alessia Simonini
Physics of Fluids
The contact angle between a gas–liquid interface and a solid surface is a function of the dynamic... more The contact angle between a gas–liquid interface and a solid surface is a function of the dynamic conditions of the contact line. Classic steady correlations link the contact angle to the contact line velocity. However, it is unclear whether they hold in the presence of inertia and the case of perfect wetting fluids. We analyze by means of experiments the shape of a liquid interface and the corresponding contact angle in accelerating conditions for two different fluids, that is, HFE7200 (perfect wetting) and demineralized water. The setup consists of a U-shaped quasi-capillary tube in which the liquid column oscillates in response to a pressure step on one of the two sides. We obtained the evolution of the interface shape from high-speed back-light visualization, fit interface models to the experimental data to estimate the contributions of all the governing forces, and perform measurements of the dynamic contact angle. We propose a new model to account for the impact of the interfa...
Journal of Coatings Technology and Research
We investigate the interface dynamics in an unsteady quasi-capillary channel flow. The configurat... more We investigate the interface dynamics in an unsteady quasi-capillary channel flow. The configuration consists of a liquid column that moves along a vertical 2D channel, open to the atmosphere and driven by a controlled pressure head. Both advancing and receding contact lines were analyzed to test the validity of classic models for dynamic wetting and to study the flow field near the interface. The operating conditions are characterized by a large acceleration, thus dominated by inertia. The shape of the moving meniscus was retrieved using Laser-Induced Fluorescence (LIF)based image processing while the flow field near was analyzed via Time-Resolved Particle Image Velocimetry (TR-PIV). The TR-PIV measurements were enhanced in the post-processing, using a combination of Proper Orthogonal Decomposition (POD) and Radial Basis Functions (RBF) to achieve super-resolution of the velocity field. Large counter-rotating vortices were observed, and their evolution was monitored in terms of the maximum intensity of the Q-field. The results show that classic contact angle models based on interface velocity cannot describe the evolution of the contact angle at a macroscopic scale. Moreover, the impact of the interface dynamics on the flow field is considerable and extends to several capillary lengths below the interface.
The purpose of the present work is the development of Planar Laser Induced Fluorescence technique... more The purpose of the present work is the development of Planar Laser Induced Fluorescence technique for temperature and concentration measurements in liquid phase of a two phase flow. The basis of technique PLIF are studied and two application are carried out:1-color PLIF and 2-color PLIF. A preliminar calibration is carried out to characterize the solution used and to study the influence of the dye as intrusive. The measurements are performed on a cell at homogeneous temperature and on the sprays. A particular setup is designed for applying the technique on the spray. Data processing is developed to select the best technique between 1-color and 2-color and study the influence of some parameter on the accuracy of the measurements. Finally, further studies are suggested with regard to some parameters that could improve accuracy
L’etude du ballottement des liquides dans leur recipient est fondamentale dans plusieurs domaines... more L’etude du ballottement des liquides dans leur recipient est fondamentale dans plusieurs domaines, specialement pour la conception des dispositifs de gestion du carburant aerospatial. D’ailleurs, la reponse dynamique aux mouvements d’un liquide dans un reservoir peut influencer facon significative la trajectoire du vehicule. Dans cette etude, le ballottement asymetrique de l’eau dans un cylindre circulaire soumis a des excitations sinusoidales externes est etudie experimentalement par velocimetrie par images de particules fluorescentes (f-PIV). L’acquisition des images PIV est realisee en phase avec un instant choisi de l’excitation externe. Les parametres utilises pour caracteriser le ballottement sont la taille du cylindre, la hauteur du liquide et la frequence du mouvement externe appliquee. La theorie relative a la geometrie utilisee est presentee pour mieux comprendre les resultats concernant les champs de vitesse et le deplacement de l’interface. Un code a ete developpe pour d...
The movement of the free liquid surface into a reservoir, better known as sloshing, is of large i... more The movement of the free liquid surface into a reservoir, better known as sloshing, is of large interest in different industrial fields such as satellites trajectory control, automotive industry, nuclear engineering, etc. Unfortunately the prediction and control of sloshing phenomenon is still hampered by the unavailability of validated theoretical models. Moreover the existing experimental studies give partial information about the behavior of the liquid/gas interface topography during sloshing, a key parameter for the validation of numerical codes.
The motion of a free liquid surface inside its container is called sloshing and it is strongly af... more The motion of a free liquid surface inside its container is called sloshing and it is strongly affected by external excitations applied to the partially filled container. It can refer to embarked containers filled of fluid, motion of cooling liquids in systems subjected to earthquake or motion of propellant inside a tank, which can influence the trajectory of vehicles. The understanding and the prediction of this particular motion is of special importance in space vehicles which are powered by cryogenic propellant. This is the case of the cryogenic upper stage where the dynamic response to sloshing can also interfere on the thermodynamics of the stored fuel. The scope of this paper is to investigate cryogenic sloshing by means of non-intrusive optical techniques and to evaluate their performances. Liquid nitrogen is used as substitute fluid of a real cryogenic propellant (LH2/LO2). Two techniques will be applied to a container partially filled with liquid nitrogen and subjected to a...
Flash-atomization can be observed when a pressurized fluid is released in an environment at lower... more Flash-atomization can be observed when a pressurized fluid is released in an environment at lower pressure. This phenomenon plays an important role in the security management of chemical industries where liquefied gases can be accidentally released at atmosphere. In other applications, for example in propulsion systems, it can have some potential benefits as it is known to produce a fine spray with enhanced atomization. The experimental characterization of these kinds of atomization should be performed by means of non-intrusive measurement techniques since they are very sensitive to external perturbation. In this work the Planar Laser Induced Fluorescence technique is used to measure the temperature variation of an ethanol superheated flashing jet. The feasibility of the technique is tested, measurements are conducted for different superheat conditions and an analysis of the measurement uncertainties is presented.
14th International Symposium on Particle Image Velocimetry, 2021
We present an experimental analysis of the flow field near an accelerating contact line using tim... more We present an experimental analysis of the flow field near an accelerating contact line using time-resolved Particle Image Velocimetry (TR-PIV). Both advancing and receding contact lines are investigated. The analyzed configuration consists of a liquid column that moves along a vertical 2D channel, open to the atmosphere and driven by a controlled pressure head. Large counter-rotating vortices were observed and analyzed in terms of the maximum intensity of the Q-field. To compute smooth spatial derivatives and improve the measurement resolution in the post-processing stage, we propose a combination of Proper Orthogonal Decomposition (POD) and Radial Basis Functions (RBF). The RBFs are used to regress the spatial and temporal structures of the leading POD modes, so that “high-resolution” modes are obtained. These can then be combined to reconstruct high-resolution fields that are smooth and robust against measurement noise and amenable to analytic differentiation. The results show si...
![Research paper thumbnail of Corrigendum to “PIV adaptive interrogation and sampling with image projection applied to water sloshing” [Exp. Therm. Fluid Sci. 102 (2019) 559–574]](https://attachments.academia-assets.com/94332394/thumbnails/1.jpg)
](Experimental Thermal and Fluid Science, 2019
Fig. 3. (a) Parameter definition in the adaptive positioning and sizing of correlation windows fo... more Fig. 3. (a) Parameter definition in the adaptive positioning and sizing of correlation windows for a given x-location. Crosses indicate the centroids of the correlation windows. (b) Refined window distribution near an oscillating interface.
Nuclear Engineering and Design, 2017
For the safety assessment of Heavy Liquid Metal nuclear reactors under seismic excitation, sloshi... more For the safety assessment of Heavy Liquid Metal nuclear reactors under seismic excitation, sloshing phenomena can be of great concern. The earthquake motions are transferred to the liquid coolant which oscillates inside the vessel, exerting additional forces on the walls and internal structures. The present study examines the case of MYRRHA, a multipurpose experimental reactor with LBE as coolant, developed by SCK•CEN. The sloshing behavior of liquid metals is studied through a comparison between mercury and water in a cylindrical tank. Experimental investigation of sloshing is carried out using optical techniques with the shaking table facility SHAKESPEARE at the von Karman Institute. Emphasis is given on the resonance case, where maximum forces occur on the tank walls. The experimental cases are reproduced numerically with the CFD software OpenFOAM, using the VOF method to track the liquid interface. The non-linear nature of sloshing is observed through visualization, where swirling is shown in the resonance case. The complex behavior is well reproduced by the CFD simulations, providing good qualitative validation of the numerical tools. A quantitative comparison of the maximum liquid elevation inside the tank shows higher values for the liquid metal than for water. Some discrepancies are revealed in CFD results and the differences are quantified. From simulations it is verified that the forces scale with the density ratio, following similar evolution in time. Overall, water is demonstrated to be a valid option as a working liquid in order to evaluate the sloshing effects, for forcing frequencies up to resonance.
Aerospace Science and Technology, 2019
Cryogenic sloshing is of primary importance in aerospace propulsion since it can affect the dynam... more 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.
Experimental Thermal and Fluid Science, 2018
The measurement of fluid velocity in the vicinity of wavy interfaces by means of Particle Image V... more 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. More
Flash atomization occurs when a liquid jet is injected in an environment where the pressure is mu... more Flash atomization occurs when a liquid jet is injected in an environment where the pressure is much lower than the liquid saturation pressure. As a consequence an enhanced atomization is observed. The modelling as well as the prediction of flashing is of an extreme importance in various industrial and scientific fields. The scope of this paper is to present the thermal characterization of a flashing jet by means of the PLIF (Planar Laser Induced Fluorescence) technique. A simplified 1D model is used to compare with the experimental data.
In this paper the asymmetric water sloshing in a partially filled circular cylindrical container ... more In this paper 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; moreover, 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 here introduced. Fluorescent Particle Image Velocimetry is used to investigate the velocity field in the liquid phase. Phase locked PIV with a selected phase of the external excitation is used 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 are compared. Selected examples of information that can be extracted from the PIV phase locked results for the sloshing phenomenon are presented.
Physics of Fluids
The contact angle between a gas–liquid interface and a solid surface is a function of the dynamic... more The contact angle between a gas–liquid interface and a solid surface is a function of the dynamic conditions of the contact line. Classic steady correlations link the contact angle to the contact line velocity. However, it is unclear whether they hold in the presence of inertia and the case of perfect wetting fluids. We analyze by means of experiments the shape of a liquid interface and the corresponding contact angle in accelerating conditions for two different fluids, that is, HFE7200 (perfect wetting) and demineralized water. The setup consists of a U-shaped quasi-capillary tube in which the liquid column oscillates in response to a pressure step on one of the two sides. We obtained the evolution of the interface shape from high-speed back-light visualization, fit interface models to the experimental data to estimate the contributions of all the governing forces, and perform measurements of the dynamic contact angle. We propose a new model to account for the impact of the interfa...
Journal of Coatings Technology and Research
We investigate the interface dynamics in an unsteady quasi-capillary channel flow. The configurat... more We investigate the interface dynamics in an unsteady quasi-capillary channel flow. The configuration consists of a liquid column that moves along a vertical 2D channel, open to the atmosphere and driven by a controlled pressure head. Both advancing and receding contact lines were analyzed to test the validity of classic models for dynamic wetting and to study the flow field near the interface. The operating conditions are characterized by a large acceleration, thus dominated by inertia. The shape of the moving meniscus was retrieved using Laser-Induced Fluorescence (LIF)based image processing while the flow field near was analyzed via Time-Resolved Particle Image Velocimetry (TR-PIV). The TR-PIV measurements were enhanced in the post-processing, using a combination of Proper Orthogonal Decomposition (POD) and Radial Basis Functions (RBF) to achieve super-resolution of the velocity field. Large counter-rotating vortices were observed, and their evolution was monitored in terms of the maximum intensity of the Q-field. The results show that classic contact angle models based on interface velocity cannot describe the evolution of the contact angle at a macroscopic scale. Moreover, the impact of the interface dynamics on the flow field is considerable and extends to several capillary lengths below the interface.
The purpose of the present work is the development of Planar Laser Induced Fluorescence technique... more The purpose of the present work is the development of Planar Laser Induced Fluorescence technique for temperature and concentration measurements in liquid phase of a two phase flow. The basis of technique PLIF are studied and two application are carried out:1-color PLIF and 2-color PLIF. A preliminar calibration is carried out to characterize the solution used and to study the influence of the dye as intrusive. The measurements are performed on a cell at homogeneous temperature and on the sprays. A particular setup is designed for applying the technique on the spray. Data processing is developed to select the best technique between 1-color and 2-color and study the influence of some parameter on the accuracy of the measurements. Finally, further studies are suggested with regard to some parameters that could improve accuracy
L’etude du ballottement des liquides dans leur recipient est fondamentale dans plusieurs domaines... more L’etude du ballottement des liquides dans leur recipient est fondamentale dans plusieurs domaines, specialement pour la conception des dispositifs de gestion du carburant aerospatial. D’ailleurs, la reponse dynamique aux mouvements d’un liquide dans un reservoir peut influencer facon significative la trajectoire du vehicule. Dans cette etude, le ballottement asymetrique de l’eau dans un cylindre circulaire soumis a des excitations sinusoidales externes est etudie experimentalement par velocimetrie par images de particules fluorescentes (f-PIV). L’acquisition des images PIV est realisee en phase avec un instant choisi de l’excitation externe. Les parametres utilises pour caracteriser le ballottement sont la taille du cylindre, la hauteur du liquide et la frequence du mouvement externe appliquee. La theorie relative a la geometrie utilisee est presentee pour mieux comprendre les resultats concernant les champs de vitesse et le deplacement de l’interface. Un code a ete developpe pour d...
The movement of the free liquid surface into a reservoir, better known as sloshing, is of large i... more The movement of the free liquid surface into a reservoir, better known as sloshing, is of large interest in different industrial fields such as satellites trajectory control, automotive industry, nuclear engineering, etc. Unfortunately the prediction and control of sloshing phenomenon is still hampered by the unavailability of validated theoretical models. Moreover the existing experimental studies give partial information about the behavior of the liquid/gas interface topography during sloshing, a key parameter for the validation of numerical codes.
The motion of a free liquid surface inside its container is called sloshing and it is strongly af... more The motion of a free liquid surface inside its container is called sloshing and it is strongly affected by external excitations applied to the partially filled container. It can refer to embarked containers filled of fluid, motion of cooling liquids in systems subjected to earthquake or motion of propellant inside a tank, which can influence the trajectory of vehicles. The understanding and the prediction of this particular motion is of special importance in space vehicles which are powered by cryogenic propellant. This is the case of the cryogenic upper stage where the dynamic response to sloshing can also interfere on the thermodynamics of the stored fuel. The scope of this paper is to investigate cryogenic sloshing by means of non-intrusive optical techniques and to evaluate their performances. Liquid nitrogen is used as substitute fluid of a real cryogenic propellant (LH2/LO2). Two techniques will be applied to a container partially filled with liquid nitrogen and subjected to a...
Flash-atomization can be observed when a pressurized fluid is released in an environment at lower... more Flash-atomization can be observed when a pressurized fluid is released in an environment at lower pressure. This phenomenon plays an important role in the security management of chemical industries where liquefied gases can be accidentally released at atmosphere. In other applications, for example in propulsion systems, it can have some potential benefits as it is known to produce a fine spray with enhanced atomization. The experimental characterization of these kinds of atomization should be performed by means of non-intrusive measurement techniques since they are very sensitive to external perturbation. In this work the Planar Laser Induced Fluorescence technique is used to measure the temperature variation of an ethanol superheated flashing jet. The feasibility of the technique is tested, measurements are conducted for different superheat conditions and an analysis of the measurement uncertainties is presented.
14th International Symposium on Particle Image Velocimetry, 2021
We present an experimental analysis of the flow field near an accelerating contact line using tim... more We present an experimental analysis of the flow field near an accelerating contact line using time-resolved Particle Image Velocimetry (TR-PIV). Both advancing and receding contact lines are investigated. The analyzed configuration consists of a liquid column that moves along a vertical 2D channel, open to the atmosphere and driven by a controlled pressure head. Large counter-rotating vortices were observed and analyzed in terms of the maximum intensity of the Q-field. To compute smooth spatial derivatives and improve the measurement resolution in the post-processing stage, we propose a combination of Proper Orthogonal Decomposition (POD) and Radial Basis Functions (RBF). The RBFs are used to regress the spatial and temporal structures of the leading POD modes, so that “high-resolution” modes are obtained. These can then be combined to reconstruct high-resolution fields that are smooth and robust against measurement noise and amenable to analytic differentiation. The results show si...
Experimental Thermal and Fluid Science, 2019
Fig. 3. (a) Parameter definition in the adaptive positioning and sizing of correlation windows fo... more Fig. 3. (a) Parameter definition in the adaptive positioning and sizing of correlation windows for a given x-location. Crosses indicate the centroids of the correlation windows. (b) Refined window distribution near an oscillating interface.
Nuclear Engineering and Design, 2017
For the safety assessment of Heavy Liquid Metal nuclear reactors under seismic excitation, sloshi... more For the safety assessment of Heavy Liquid Metal nuclear reactors under seismic excitation, sloshing phenomena can be of great concern. The earthquake motions are transferred to the liquid coolant which oscillates inside the vessel, exerting additional forces on the walls and internal structures. The present study examines the case of MYRRHA, a multipurpose experimental reactor with LBE as coolant, developed by SCK•CEN. The sloshing behavior of liquid metals is studied through a comparison between mercury and water in a cylindrical tank. Experimental investigation of sloshing is carried out using optical techniques with the shaking table facility SHAKESPEARE at the von Karman Institute. Emphasis is given on the resonance case, where maximum forces occur on the tank walls. The experimental cases are reproduced numerically with the CFD software OpenFOAM, using the VOF method to track the liquid interface. The non-linear nature of sloshing is observed through visualization, where swirling is shown in the resonance case. The complex behavior is well reproduced by the CFD simulations, providing good qualitative validation of the numerical tools. A quantitative comparison of the maximum liquid elevation inside the tank shows higher values for the liquid metal than for water. Some discrepancies are revealed in CFD results and the differences are quantified. From simulations it is verified that the forces scale with the density ratio, following similar evolution in time. Overall, water is demonstrated to be a valid option as a working liquid in order to evaluate the sloshing effects, for forcing frequencies up to resonance.
Aerospace Science and Technology, 2019
Cryogenic sloshing is of primary importance in aerospace propulsion since it can affect the dynam... more 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.
Experimental Thermal and Fluid Science, 2018
The measurement of fluid velocity in the vicinity of wavy interfaces by means of Particle Image V... more 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. More
Flash atomization occurs when a liquid jet is injected in an environment where the pressure is mu... more Flash atomization occurs when a liquid jet is injected in an environment where the pressure is much lower than the liquid saturation pressure. As a consequence an enhanced atomization is observed. The modelling as well as the prediction of flashing is of an extreme importance in various industrial and scientific fields. The scope of this paper is to present the thermal characterization of a flashing jet by means of the PLIF (Planar Laser Induced Fluorescence) technique. A simplified 1D model is used to compare with the experimental data.
In this paper the asymmetric water sloshing in a partially filled circular cylindrical container ... more In this paper 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; moreover, 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 here introduced. Fluorescent Particle Image Velocimetry is used to investigate the velocity field in the liquid phase. Phase locked PIV with a selected phase of the external excitation is used 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 are compared. Selected examples of information that can be extracted from the PIV phase locked results for the sloshing phenomenon are presented.