Etude numérique et expérimentale de l’interaction entre deux écoulements compressibles dans un éjecteur supersonique

The work reported in this thesis relates to the experimental and numerical studies of the flow within a supersonic ejector. The flow pattern which occurs in these apparatuses is very complex because of the flow phenomena encountered like flow turbulence and shock waves. The experimental methods used are the measurement of the pressure along the axis of the ejector using a specific probe developed for this purpose, the flow visualization by laser tomography and the velocity measurement by PIV. The numerical simulations are carried out using the Ansys-Fluent code with 2D axisymmetric and 3D models. First, a study of sensitivity to the numerical parameters of simulation and to the turbulence models is carried out on the ejector operating without induced flow. The validation of the simulations is achieved by a comparison between the numerical results and velocity measurements by PIV. A 3D model is necessary for the simulation of the flow in the ejector operating with induced flow because of the complex ejector geometry. The experimental techniques and the numericalmodels developed make it possible to analyze the interaction of the primary and secondary flows, in particular the process of recompression by oblique shocks and the mixing process. An attempt at modeling by LES simulation the flow instabilities detected during experiments is also approached.Le travail mené dans le cadre de cette thèse porte sur l’étude expérimentale et numérique de l’écoulement au sein d’un éjecteur supersonique. Le régime d’écoulement qui s’installe dans ces appareils est très complexe du fait des phénomènes physiques qui les caractérisent comme la turbulence et les ondes de choc. Les méthodes expérimentales utilisées sont la mesure de la pression le long de l’axe de l’éjecteur `a l’aide d’une sonde développée à cet effet, la visualisation de l’écoulement par tomographie laser et la mesure de vitesse par PIV. Les simulations numériques sont réalisées à l’aide du code Ansys-Fluent en 2D axisymétrique et en 3D. Dans un premier temps, une étude de sensibilité du modèle numérique portant sur les paramètres de simulations et les modèles de turbulence est menée sur l’éjecteur fonctionnant sans flux induit. La validation des simulations repose sur une comparaison des résultats numériques avec des mesures de vitesse par PIV. Un modèle 3D s’est avéré incontournable pour l’étude de l’écoulement dans l’éjecteur avec flux induit à cause de sa géométrie complexe. Les outils expérimentaux et numériques développés permettent d’analyser finement l’interaction des flux moteur et induit, en particulier les processus de recompression par chocs obliques et de mélange. Une tentative de modélisation par LES des instabilités de l’écoulement détectées expérimentalement est également abordée

Etude numérique et expérimentale du processus de recompression le long d'un éjecteur supersonique

Un éjecteur est un assemblage de 2 tuyères coaxiales, soumis à un processus complexe de recompression par chocs obliques. Ce processus est analysé en suivant la pression statique le long de l'axe de l'éjecteur. Le système de mesure développé consiste en un tube capillaire, doté d'un orifice permettant la prise de la pression, pouvant se translater le long de l'éjecteur. Des simulations numériques sont par ailleurs réalisées utilisant des modèles de turbulence RANS. La comparaison expérimental-numérique montre une bonne cohérence malgré un léger décalage dans le nombre et l'amplitude des chocs

Visualisations expérimentales et numériques des instabilités dans un éjecteur air -air supersonique

L'écoulement qui prend place dans un éjecteur supersonique met en jeu de nombreux processus complexes. Il peut être notamment le siège d'instabilités qui peuvent être détectées et visualisées grâce à l'utilisation d'un éclairage pulsé lors de visualisations expérimentales de l'écoulement et par des simulations CFD 3D instationnaires avec modélisation LES

Multifunctional, Self-Cleaning Air Filters Based on Graphene-Enhanced Ceramic Networks

Particulate air pollution is taking a huge toll on modern society, being associated with more than three million deaths per year. In addition, airborne infectious microorganism can spread dangerous diseases, further elevating the problem. A common way to mitigate the risks of airborne particles is by air filtration. However, conventional air filters usually do not provide any functionality beyond particle removal. They are unable to inactivate accumulated contaminants and therefore need periodic maintenance and replacement to remain operational and safe. This work presents a multifunctional, self-cleaning air filtration system which utilizes a novel graphene-enhanced air filter medium (GeFM). The hybrid network of the GeFM combines the passive structure-based air filtration properties of an underlying ceramic network with additional active features based on the functional properties of a graphene thin film. The GeFM is able to capture >95 % of microorganisms and particles larger than 1 $\mu$m and can be repetitively Joule-heated to >300 {\deg}C for several hours without signs of degradation. Hereby, built-up organic particulate matter and microbial contaminants are effectively decomposed, regenerating the GeFM. Additionally, the GeFM provides unique options to monitor the filter's air troughput and loading status during operation. The active features of the GeFM can drastically improve filter life-time and safety, offering great potential for the development of safer and more sustainable air filtration solutions to face the future challenges of air pollution and pandemics.Comment: * Corresponding authors: Prof. Dr. Rainer Adelung ([email protected]) and Dr.-Ing. Fabian Sch\"utt ([email protected]

Reuse of medical face masks in domestic and community settings without sacrificing safety: Ecological and economical lessons from the Covid-19 pandemic

The need for personal protective equipment increased exponentially in response to the Covid-19 pandemic. To cope with the mask shortage during springtime 2020, a French consortium was created to find ways to reuse medical and respiratory masks in healthcare departments. The consortium addressed the complex context of the balance between cleaning medical masks in a way that maintains their safety and functionality for reuse, with the environmental advantage to manage medical disposable waste despite the current mask designation as single-use by the regulatory frameworks. We report a Workflow that provides a quantitative basis to determine the safety and efficacy of a medical mask that is decontaminated for reuse. The type IIR polypropylene medical masks can be washed up to 10 times, washed 5 times and autoclaved 5 times, or washed then sterilized with radiations or ethylene oxide, without any degradation of their filtration or breathability properties. There is loss of the antiprojection properties. The Workflow rendered the medical masks to comply to the AFNOR S76-001 standard as “type 1 non-sanitory usage masks”. This qualification gives a legal status to the Workflow-treated masks and allows recommendation for the reuse of washed medical masks by the general population, with the significant public health advantage of providing better protection than cloth-tissue masks. Additionally, such a legal status provides a basis to perform a clinical trial to test the masks in real conditions, with full compliance with EN 14683 norm, for collective reuse. The rational reuse of medical mask and their end-of-life management is critical, particularly in pandemic periods when decisive turns can be taken. The reuse of masks in the general population, in industries, or in hospitals (but not for surgery) has significant advantages for the management of waste without degrading the safety of individuals wearing reused masks

Numerical and experimental study of the interaction of two compressible flows in supersonic air ejector

Le travail mené dans le cadre de cette thèse porte sur l’étude expérimentale et numérique de l’écoulement au sein d’un éjecteur supersonique. Le régime d’écoulement qui s’installe dans ces appareils est très complexe du fait des phénomènes physiques qui les caractérisent comme la turbulence et les ondes de choc. Les méthodes expérimentales utilisées sont la mesure de la pression le long de l’axe de l’éjecteur `a l’aide d’une sonde développée à cet effet, la visualisation de l’écoulement par tomographie laser et la mesure de vitesse par PIV. Les simulations numériques sont réalisées à l’aide du code Ansys-Fluent en 2D axisymétrique et en 3D. Dans un premier temps, une étude de sensibilité du modèle numérique portant sur les paramètres de simulations et les modèles de turbulence est menée sur l’éjecteur fonctionnant sans flux induit. La validation des simulations repose sur une comparaison des résultats numériques avec des mesures de vitesse par PIV. Un modèle 3D s’est avéré incontournable pour l’étude de l’écoulement dans l’éjecteur avec flux induit à cause de sa géométrie complexe. Les outils expérimentaux et numériques développés permettent d’analyser finement l’interaction des flux moteur et induit, en particulier les processus de recompression par chocs obliques et de mélange. Une tentative de modélisation par LES des instabilités de l’écoulement détectées expérimentalement est également abordée.The work reported in this thesis relates to the experimental and numerical studies of the flow within a supersonic ejector. The flow pattern which occurs in these apparatuses is very complex because of the flow phenomena encountered like flow turbulence and shock waves. The experimental methods used are the measurement of the pressure along the axis of the ejector using a specific probe developed for this purpose, the flow visualization by laser tomography and the velocity measurement by PIV. The numerical simulations are carried out using the Ansys-Fluent code with 2D axisymmetric and 3D models. First, a study of sensitivity to the numerical parameters of simulation and to the turbulence models is carried out on the ejector operating without induced flow. The validation of the simulations is achieved by a comparison between the numerical results and velocity measurements by PIV. A 3D model is necessary for the simulation of the flow in the ejector operating with induced flow because of the complex ejector geometry. The experimental techniques and the numericalmodels developed make it possible to analyze the interaction of the primary and secondary flows, in particular the process of recompression by oblique shocks and the mixing process. An attempt at modeling by LES simulation the flow instabilities detected during experiments is also approached

Development and testing of a pressure probe for centerline static pressure measurement in supersonic nozzles and ejectors

International audienceThis work describes the development and testing of a system for measuring static pressure along the axis of supersonic flow devices such as convergent–divergent nozzles or ejectors. The pressure probe consists of a capillary tube positioned at the ejector centerline. A hole is perforated perpendicularly on the wall of the thin tube to capture and deport the static pressure measurement to a piezoelectric sensor located at one extremity of the tube outside the ejector. The measurements obtained are compared with numerical results from computational fluid dynamics simulations and wall pressure measurements. The first tests demonstrate the good capability of the pressure probe to detect shocks occurring in the flow and to provide continuous axial distributions of the static pressure

CFD Design Study of a Pressure Probe for Centerline Static Pressure Measurement in Supersonic Ejectors

International audienceThe measurement of the static pressure of the flow inside a supersonic ejector can be achieved by using a thin tube with a radially drilled hole to capture the flow pressure, and which is inserted along the ejector axis. This paper presents a numerical study by CFD permitting to predict the disturbances generated by the presence of the probe in the ejector. Also this study allows guiding the design of the probe, in particular of the capillary tube diameter for the least disturbed measurement. A probe prototype has been built and tested on an ejector test bench

Flow visualization in supersonic ejectors using laser tomography techniques

International audienceThis paper presents flow imaging techniques developed for investigating flow in ejectors. These visualization techniques use the laser sheet method but differ from each other by the kind of the illumination source, the polarization direction of the incident light and thetype of the scattering tracers. Each of these methods enables the visualization of specific phenomena (shock structure, flow instabilities, mixing process). Although the flow visualizations are primarily qualitative, they allow the determination of the flow regime, the measurement of the non-mixing length, can indicate suggestions for the design of ejectors and provide the possibility to validate numerical simulations

Visualization of flow instabilities in supersonic ejectors using Large Eddy Simulation

International audienc