Cavitation Erosion Mechanism: Numerical Sumulations of the Interaction Between Pressure Waves and Solid Boundaries

To evaluate the aggressiveness power of cavitating flows and to improve prediction methods for cavitation erosion, the pressure waves emitted during bubble collapses were studied and simulated by means of the Keller's and Fujikawa and Akamatsu's physical models. The profile and the energy of the pressure waves emitted during cavity collapse were evaluated by numerical simulation. The dynamic response and the surface deformation (i.e., pit profile and pit volume) of various materials exposed to pressure wave impacts was simulated making use of a 2D axisymmetric numerical code simulating the interaction between pressure wave and an elastoplastic solid. Making use of numerical results, a new parameter b (defined as the ratio between the pressure wave energy and the generated pit volume) was introduced and evaluated for three materials (aluminum, copper and stainless steel). By associating numerical simulations and experimental results concerning pitted samples exposed to cavitating flows (volume damage rate), the pressure wave power density was introduced. This physical property of the flow characterizes the cavitation aggressiveness and can be related to the flow hydrodynamic conditions. Associated to b parameter, the pressure wave power density appeared to be a useful tool to predict the cavitation erosion power

Mécanismes d'interactions fluide/structure et de transfert d'énergie en érosion de cavitation

L'érosion de cavitation se caractérise dans un premier temps par une période de marquage sans perte de masse. Afin d'étudier cette phase, une étude locale a tout d'abord été effectuée : une approche énergétique des ondes de surpressions émises lors du collapsus d'une bulle et de leur interaction avec une paroi solide a été réalisée. Cette approche a mis en évidence un paramètre caractéristique du marquage reliant la déformation finale à l'énergie de l'onde impactante ne dépendant que des propriétés mécanique du matériau. Une comparaison expérimentale a donné une première validation de notre modèle local. Nous avons étendu ce modèle à un aspect global avec l'introduction d'une puissance potentielle liée à l'hydrodynamique de l'écoulement cavitant et d'un rendement d'agressivité caractérisant l'agressivité d'un écoulement vis à vis d'un matériau. Une comparaison avec deux expériences menées à EDF a permis de donner une première validation de notre approche.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Bottom right?: Work, worldviews, and political positions in the bottom right quarter of the social space

This article revisits the debate on the shift to the right of the working classes and advocates for a relational and localized approach in order to take a different look at these questions, starting from the concept of social space as defined by Pierre Bourdieu. The goal is to analyze the relationship to politics of groups with rather few resources (located in the lower half of the social space), but with relatively more economic capital than cultural capital (located on the right of the social space). By seeking to perceive the differences among poorly endowed groups, we give ourselves the means to think in subtle shades about a phenomenon (the right-wing and far-right vote) that is neither entirely new nor uniform. Immersion fieldworks appear to be particularly well suited to capture the social logics at work in the distant relationships to politics that often characterize these groups. The introduction then presents the main results of the research on the “bottom right” quarter gathered in this special issue. The text thus addresses the place of work, the worldviews that result from the configurations in which groups are taken, and the decisive role of the political offer in the conversion of these worldviews into political positions.Cet article revient sur le débat sur la droitisation des classes populaires et défend une approche relationnelle et localisée en s’appuyant sur le concept d’espace social tel que défini par P. Bourdieu. L’objectif est d’analyser le rapport au politique de groupes ayant plutôt peu de ressources (situés dans la moitié basse de l’espace social), mais disposant de relativement plus de capital économique que de capital culturel (situés à droite de l’espace social). En cherchant à percevoir les différences au sein des groupes peu dotés, on se donne les moyens de penser dans la nuance un phénomène (le vote à droite et à l’extrême droite) qui n’est ni tout à fait nouveau ni uniforme. Les enquêtes par immersion apparaissent particulièrement ajustées pour saisir les logiques sociales à l’œuvre dans les relations distantes au politique qui caractérisent souvent ces groupes. Cette introduction présente enfin les principaux résultats qui ressortent des recherches sur le quart « en bas à droite » réunies dans ce dossier. Le texte aborde ainsi la place du travail, les visions du monde qui résultent des configurations dans lesquelles sont pris les groupes, et le rôle déterminant de l’offre politique dans la conversion de ces visions du monde en prises de position politiques

Study of pressure wave emitted during spherical bubble collapse

International audienc

Study of pressure wave emitted during spherical bubble collapse

International audienc

Interaction between pressure waves and spherical cavitation bubbles: discussions about cavitation erosion mechanism

International audienc

"Le crépuscule de l’encadrement politique territorialisé ? Différenciation socio-spatiale du travail de campagne et déprises partisanes"

International audienc

Interaction between pressure waves and spherical cavitation bubbles: discussions about cavitation erosion mechanism

International audienc

Energy Balance in Cavitation Erosion: From Bubble Collapse to Indentation of Material Surface

International audienceAn original approach based on energy balance between vapor bubble collapse, emitted pressure wave, and neighboring solid wall response was proposed, developed, and tested to estimate the aggressiveness of cavitating flows. In the first part of the work, to improve a prediction method for cavitation erosion (Fortes-Patella and Reboud, 1998, “A New Approach to Evaluate the Cavitation Erosion Power,” ASME J. Fluids Eng., 120(2), pp. 335–344; Fortes-Patella and Reboud, 1998, “Energetical Approach and Impact Efficiency in Cavitation Erosion,” Proceedings of Third International Symposium on Cavitation, Grenoble, France), we were interested in studying the pressure waves emitted during bubble collapse. The radial dynamics of a spherical vapor/gas bubble in a compressible and viscous liquid was studied by means of Keller's and Fujikawa and Akamatsu's physical models (Prosperetti, 1994, “Bubbles Dynamics: Some Things we did not Know 10 Years Ago,” Bubble Dynamics and Interface Phenomena, Blake, Boulton-Stone, Thomas, eds., Kluwer Academic Publishers, Dordrecht, the Netherlands, pp. 3–15; Fujikawa and Akamatsu, 1980, “Effects of Non-Equilibrium Condensation of Vapor on the Pressure Wave Produced by Collapse of a Bubble in Liquid,” J. Fluid Mech., 97(3), pp. 481–512). The pressure amplitude, the profile, and the energy of the pressure waves emitted during cavity collapses were evaluated by numerical simulations. The model was validated by comparisons with experiments carried out at Laboratoire Laser, Plasma et Procédés Photoniques (LP3-IRPHE) (Marseille, France) with laser-induced bubble (Isselin et al., 1998, “Investigations of Material Damages Induced by an Isolated Vapor Bubble Created by Pulsed Laser,” Proceedings of Third International Symposium on Cavitation, Grenoble, France; Isselin et al., 1998, “On Laser Induced Single Bubble Near a Solid Boundary: Contribution to the Understanding of Erosion Phenomena,” J. Appl. Phys., 84(10), pp. 5766–5771). The efficiency of the first collapse ηwave/bubble (defined as the ratio between pressure wave energy and initial bubble potential energy) was evaluated for different bubble collapses. For the cases considered of collapse in a constant-pressure field, the study pointed out the strong influence of the air contents on the bubble dynamics, on the emitted pressure wave characteristics, and on the collapse efficiency. In the second part of the study, the dynamic response and the surface deformation (i.e., pit profile and pit volume) of various materials exposed to pressure wave impacts was simulated making use of a 2D axisymmetric numerical code simulating the interaction between pressure wave and an elastoplastic solid. Making use of numerical results, a new parameter β (defined as the ratio between the pressure wave energy and the generated pit volume) was introduced and evaluated for three materials (aluminum, copper, and stainless steel). By associating numerical simulations and experimental results concerning pitted samples exposed to cavitating flows (volume damage rate), the pressure wave power density and the flow aggressiveness potential power were introduced. These physical properties of the flow characterize the cavitation intensity and can be related to the flow hydrodynamic conditions. Associated to β and ηwave/bubble parameters, these power densities appeared to be useful tools to predict the cavitation erosion power