Search

Cardiovascular diseases are the leading cause of mortality in the industrialized world. Among these diseases, aortic dissection affects the aorta wall and is a surgical emergency with a low survival rate. This pathology occurs when an injury leads to a localized tear of the innermost layer of the aorta. It allows blood to flow between the layers of the aortic wall, forcing the layers apart and creating a false lumen. Endovascular treatment seeks to obliterate the entrances to the false lumen with a covered stent. There are very few studies on the postoperative demonstration of blood flow phenomena in the aortic dissection endovascular treatment. It is crucial to study the hemodynamics of blood in the aorta after an intervention because the new geometrical configuration of the aorta with a stent leads to modifications in blood flow. For the surgeons, the procedure can only be performed empirically, using MRI-4D images to view the postoperative flow of the patient’s blood in the aorta with the stent. This paper aims to present a numerical tool developed from the open-source software FOAM- Extend®, allowing for multiphysics numerical simulations. Using MRI data, a bio-faithful model of the patient-specific case was built. Numerical simulations were performed to predict preoperative and postoperative (endovascular treatment) hemodynamics. The modifications of the flow in the aorta were analyzed focusing on the postoperative perfusions. The results were compared with the corresponding MRI data and have a good qualitative agreement. Biomarkers are calculated to localize possible zones of post-operative pathological developments and recommendations may be suggested to the surgeons.

Shot peening is commonly used as an effective method to extend the service life of parts and reduce the residual tensile stresses. The main principle of this surface treatment method is to introduce compressive residual stresses into parts, thereby preventing the crack-propagation. Water cavitation peening (WCP) is a recent technology that allows generating high-intensity pressure waves and micro-jet at the surface of parts via a cavitating jet. However, it is a challenge to predict the pressure intensity at the treatment surface and therefore being able to make predictive modelization of the process. To anticipate the pressure distribution around the cavitating jet, a multiple steps approach has been developed. First, through the study of a single cavitation bubble, understand the pressure pulse generated by a single bubble during its collapse process. The second step is to establish a numerical simulation of the cavitating jet near the nozzle with ANSYS Fluent. Accordingly, the cavitation area and the vapor volume fraction at different section of cavitating jet will be predicted. Then, the mechanical loading at the surface of parts will be defined by these sources. The second part of the approach is here studied. The simulation results will be compared with experimental high-speed camera imaging of the cavitating jet.

La maîtrise du procédé de grenaillage par jet d'eau cavitant nécessite une meilleure compréhension des mécanismes physiques en jeu. Ceci implique le recours à une instrumentation fine afin d'exploiter les paramètres pertinents de fonctionnement. Dans cette perspective, un banc expérimental basique a été mis en place. Il permet de montrer la faisabilité d'une mesure quantitative de pression vue par une surface au moment de l'implosion dans son voisinage d'une bulle de cavitation. Cette mesure est réalisée grâce à un capteur en poly(fluorure de vinylidène) PVDF. Ces mesures sont corrélées à un modèle analytique s'appuyant sur des enregistrements vidéo à haute cadence.

International audience

Since the end of the 1990's, a new method of optical flow visualisation called Molecuar Tagging Velocimetry (MTV) has been under developement. Its principle is based on the use of phosphorescent supramolecules which, once excited by an ultraviolet laser pulse, emit a bright visible radiation during a relatively long time compared to fluorescence (up to a few milliseconds). This property is what allows the molecules to be used as Lagragian tracers for the flow, leading to the determination of the velocity field at each point of the tagged area. Moreover, the dependency of phosphorescence upon several scalar properties of the flow such as temperature, concentration or pH enables the 1 22 ème Congrès Français de Mécanique Lyon, 24 au 28 Août 2015 determination of this specific scalar field through the observation of the the flow's local radiated intensity. The main purpose of this study is to apply the MTV technique to the observation of mass transfer phenomenum in multi-phase flows., Depuis la fin des années 1990 se développe une nouvelle méthode de diagnostic optique appelée marquage moléculaire ou MTV (Molecular Tagging Velocimetry). Le principe de cette technique repose sur l'utilisation de supramolécules qui une fois excitées par impulsion lumineuse dans l'ultraviolet vont phosphorescer dans le visible sur une durée bien plus importante que les temps caractéristiques de la fluorescence (jusqu'à quelques millisecondes). Cette propriété permet de les utiliser comme marqueurs lagrangiens de l'écoulement pour ainsi déterminer le champ de vitesse en tout point de la zone marquée. La dépendance de la phosphorescence à diérents scalaires passifs du fluide tels que la température, le pH, la concentration permettent également de déduire le champ de ce scalaire à partir de l'intensité locale de la réponse lumineuse de l'écoulement. L'objectif de cette étude est d'appliquer la technique de MTV à l'observation du transfert de masse en écoulement diphasique gaz-liquide.

International audience