Flow and air-entrainment around partially submerged vertical cylinders

In this study, a partially submerged vertical cylinder is moved at constant velocity through water, which is initially at rest. During the motion, the wake behind the cylinder induces free-surface deformation. Eleven cylinders, with diameters from $D=1.4$ to 16 cm, were tested at two different conditions: (i) constant immersed height $h$ and (ii) constant $h/D$. The range of translation velocities and diameters are in the regime of turbulent wake with experiments carried out for $4500<Re<240 \,000$ and $0.2<Fr<2.4$, where $Re$ and $Fr$ are the Reynolds and Froude numbers based on $D$. The focus here is on drag force measurements and relatively strong free-surface deformation up to air-entrainment. Specifically, two modes of air-entraiment have been uncovered: (i) in the cavity along the cylinder wall and (ii) in the wake of the cylinder. A scaling for the critical velocity for air-entrainment in the cavity has been observed in agreement with a simple model. Furthermore, for $Fr>1.2$, the drag force varies linearly with $Fr$

Free-floating molecular clumps and gas mixing: hydrodynamic aftermaths of the intracluster−-interstellar medium interaction

The interaction of gas-rich galaxies with the intra-cluster medium (ICM) of galaxy clusters has a remarkable impact on their evolution, mainly due to the gas loss associated with this process. In this work, we use an idealised, high-resolution simulation of a Virgo-like cluster, run with RAMSES and with dynamics reproducing that of a zoom cosmological simulation, to investigate the interaction of infalling galaxies with the ICM. We find that the tails of ram pressure stripped galaxies give rise to a population of up to more than a hundred clumps of molecular gas lurking in the cluster. The number count of those clumps varies a lot over time -- they are preferably generated when a large galaxy crosses the cluster (M$_{200c} > 10^{12}$ M$_\odot$), and their lifetime ($\lesssim 300$ Myr) is small compared to the age of the cluster. We compute the intracluster luminosity associated with the star formation which takes place within those clumps, finding that the stars formed in all of the galaxy tails combined amount to an irrelevant contribution to the intracluster light. Surprisingly, we also find in our simulation that the ICM gas significantly changes the composition of the gaseous disks of the galaxies: after crossing the cluster once, typically 20% of the cold gas still in those disks comes from the ICM.Comment: 9 pages, 6 figures. Accepted for publication in MNRA

Numerical and experimental studies of the flow around a partially submerged vertical cylinder

International audienceL'écoulement et l'injection d'air autour d'un cylindre vertical partiellement immergé, en translation, est étudié expérimentalement et numériquement. Le régime d'écoulement est turbulent avec 15 000 < Re < 60 000 et 0.4 < F r < 1.7, où Re et F r sont les nombres de Reynolds et de Froude adimensionnés à l'aide du diamètre D du cylindre. Une cavité à l'aval du cylindre est observée. L'objectif de ce travail est d'étudier les efforts de traînée, l'élévation de la surface libre et la vitesse critique à partir de laquelle il y a entraînement d'air. Un bon accord entre les expériences et les simulations a été trouvé, évaluant ainsi la profondeur de la cavité, le coefficient de traînée et la vitesse critique d'injection d'air. Abstract : The flow around a vertical cylinder piercing the free-surface is studied experimentally and numerically. The cylinder has a free-end and the range of velocities are in the regime of turbulent wake with experiments and simulations carried out for 15 000 < Re < 60 000 and 0.4 < F r < 1.7, where Re and F r are the Reynolds and Froude numbers based on the cylinder diameter D. A cavity downstream the cylinder is observed. The focus here is on drag force measurement, free-surface elevation, and critical velocity for air-entrainment. Specifically, a good agreement between experiments and simulations is obtained for the cavity depth, the drag coefficient and the critical velocity

Étude expérimentale de l'éclatement tourbillonnaire en bordure d'une plaque immergée sous la houle

L'interaction de la houle avec une structure immergée génère des filaments tourbillonnaires très intenses qui ont un fort impact sur leur environnement proche. La dynamique de ces filaments présente des mécanismes de déstabilisation fortement tridimensionnels dont la caractérisation représente un défi expérimental. Pour identifier et comprendre ces mécanismes, nous avons utilisé l'holographie numérique dans l'axe, par afin d'accéder à la distribution tridimensionnelle des vitesses au sein du tourbillon et ainsi mieux comprendre la nature des processus intervenant dans sa déstabilisation. Ses mesures sont complétées par des mesures en stéréo-piv afin de valider les résultats obtenus par holographie

Experiments and Simulations of Free-Surface Flow behind a Finite Height Rigid Vertical Cylinder

We present the results of a combined experimental and numerical study of the free-surface flow behind a finite height rigid vertical cylinder. The experiments measure the drag and the wake angle on cylinders of different diameters for a range of velocities corresponding to 30,000 &lt;Re&lt; 200,000 and 0.2&lt;Fr&lt;2 where the Reynolds and Froude numbers are based on the diameter. The three-dimensional large eddy simulations use a conservative level-set method for the air-water interface, thus predicting the pressure, the vorticity, the free-surface elevation and the onset of air entrainment. The deep flow looks like single phase turbulent flow past a cylinder, but close to the free-surface, the interaction between the wall, the free-surface and the flow is taking place, leading to a reduced cylinder drag and the appearance of V-shaped surface wave patterns. For large velocities, vortex shedding is suppressed in a layer region behind the cylinder below the free surface. The wave patterns mostly follow the capillary-gravity theory, which predicts the crest lines cusps. Interestingly, it also indicates the regions of strong elevation fluctuations and the location of air entrainment observed in the experiments. Overall, these new simulation results, drag, wake angle and onset of air entrainment, compare quantitatively with experiments

The effect of cooling press on the encapsulation properties of crystalline photovoltaic modules: residual stress and adhesion

A high-quality encapsulation process is crucial to ensuring the performance and long-term reliability of photovoltaic (PV) modules. In crystalline Si technology-based modules, poly (ethylene-co-vinyl acetate) (EVA) is the most widely used PV encapsulant. Its encapsulation process is usually performed in a flat-bed vacuum bag laminator. In certain types of laminators, cooling press can be applied to the module cooling process after the module encapsulation, leading to a much higher cooling rate (similar to 100 degrees C/min) than conventional natural cooling due to the application of water cooling circulation and mechanical pressure on the modules. In this work, the effect of the cooling press on the encapsulation properties of PV modules with EVA as the encapsulant are assessed on the aspects of residual stress in the modules, peeling strength between glass and EVA, and the resulting EVA gel content after encapsulation. The results show that the cooling press influences the encapsulation properties of PV modules. In particular by applying the cooling press after encapsulation, the residual normal stress in the Si solar cell in the encapsulated module after cooling can be reduced by as much as 22 +/- 2 to 27 +/- 3% depending on the EVA gel content, whereas the peeling strength between front glass and EVA is increased by similar to 10%. This work should help the further optimization of PV module encapsulation processes aimed at improving module encapsulation quality. Copyright (C) 2013 John Wiley & Sons, Ltd

Compressive-shear adhesion characterization of polyvinyl-butyral and ethylene-vinyl acetate at different curing times before and after exposure to damp-heat conditions

Photovoltaic (PV) module efficiency and reliability are two factors that have an important impact on the final cost of the PV electricity production. It is widely accepted that a good adhesion between the encapsulant and the different substrates of a PV module is needed to ensure long-term reliability. Several testing procedures exist that use a metric derived from the force at interface failure to characterize the adhesion. It has, however, not been demonstrated that those metrics relate directly to the interfacial adhesion (defined as the surface energy density needed to break interfacial bonds), and the obtained results usually relate to an apparent adhesion strength. In this work, we describe a new design for compressive-shear testing of polymer layers bonded to rigid substrates. We use it to characterize real interfacial adhesion of ethylene-vinyl acetate (EVA) and polyvinyl-butyral (PVB) to a glass substrate before and after degradation in damp-heat. Our results show that a peak-force based metric is unable to capture the evolution of adhesion through degradation, and a new metric based on the elastic strain energy of the encapsulant is proposed. Moreover, we show that PVB adhesion to glass is much more affected by damp-heat exposure where polymer saturation takes place, in comparison with the adhesion of EVA to glass. The presented characterization protocol is a powerful tool that can help in assessing the reliability of an encapsulant facing specific degradation conditions. Copyright © 2012 John Wiley & Sons, Ltd

In Situ Identification of Plant-Invasive Bacteria with MALDI-TOF Mass Spectrometry

Rhizobia form a disparate collection of soil bacteria capable of reducing atmospheric nitrogen in symbiosis with legumes. The study of rhizobial populations in nature involves the collection of large numbers of nodules found on roots or stems of legumes, and the subsequent typing of nodule bacteria. To avoid the time-consuming steps of isolating and cultivating nodule bacteria prior to genotyping, a protocol of strain identification based on the comparison of MALDI-TOF MS spectra was established. In this procedure, plant nodules were considered as natural bioreactors that amplify clonal populations of nitrogen-fixing bacteroids. Following a simple isolation procedure, bacteroids were fingerprinted by analysing biomarker cellular proteins of 3 to 13 kDa using Matrix Assisted Laser Desorption/Ionization Time of Flight (MALDI-TOF) mass spectrometry. In total, bacteroids of more than 1,200 nodules collected from roots of three legumes of the Phaseoleae tribe (cowpea, soybean or siratro) were examined. Plants were inoculated with pure cultures of a slow-growing Bradyrhizobium japonicum strain G49, or either of two closely related and fast-growing Sinorhizobium fredii strains NGR234 and USDA257, or with mixed inoculants. In the fully automatic mode, correct identification of bacteroids was obtained for >97% of the nodules, and reached 100% with a minimal manual input in processing of spectra. These results showed that MALDI-TOF MS is a powerful tool for the identification of intracellular bacteria taken directly from plant tissues

nIFTy galaxy cluster simulations – II. Radiative models

We have simulated the formation of a massive galaxy cluster (M$_{200}^{\rm crit}$ = 1.1$\times$10$^{15}h^{-1}M_{\odot}$) in a $\Lambda$CDM universe using 10 different codes (RAMSES, 2 incarnations of AREPO and 7 of GADGET), modeling hydrodynamics with full radiative subgrid physics. These codes include Smoothed-Particle Hydrodynamics (SPH), spanning traditional and advanced SPH schemes, adaptive mesh and moving mesh codes. Our goal is to study the consistency between simulated clusters modeled with different radiative physical implementations - such as cooling, star formation and AGN feedback. We compare images of the cluster at $z=0$, global properties such as mass, and radial profiles of various dynamical and thermodynamical quantities. We find that, with respect to non-radiative simulations, dark matter is more centrally concentrated, the extent not simply depending on the presence/absence of AGN feedback. The scatter in global quantities is substantially higher than for non-radiative runs. Intriguingly, adding radiative physics seems to have washed away the marked code-based differences present in the entropy profile seen for non-radiative simulations in Sembolini et al. (2015): radiative physics + classic SPH can produce entropy cores. Furthermore, the inclusion/absence of AGN feedback is not the dividing line -as in the case of describing the stellar content- for whether a code produces an unrealistic temperature inversion and a falling central entropy profile. However, AGN feedback does strongly affect the overall stellar distribution, limiting the effect of overcooling and reducing sensibly the stellar fraction.Comment: 20 pages, 13 figures, submitted to MNRA

New challenges in solar architectural innovation

Among the century’s main challenges, climate change and the need for energy sources diversification are of great importance. In this context, renewable energies undoubtedly have an important role to play. Photovoltaic (PV) electricity is especially well suited to face these energy challenges. It is now established that the low thin film photovoltaic panels production costs will allow, even in continental climate, to reach low electricity cost, providing easy installation, public acceptance and high reliability. However, architectural considerations are often neglected in the current integration of PV panels. Taking into consideration specific architectural aspects like the surface appearance and the colour of the PV modules can become the key for the successful development of new, well integrated solar systems. To achieve this goal, our team, within the Archinsolar [1] project framework, works on the development of new generation of photovoltaic elements based on silicon thin films technologies (amorphous and micromoph). These new elements will be ultra-reliable and manufacturable at a very low cost, allowing a good architectural integration, respectful of the environment, landscape and built environment. Genera