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The inhalation route has a substantial influence on the fate of inhaled particles. An outbreak of infectious diseases such as COVID-19, influenza or tuberculosis depends on the site of deposition of the inhaled pathogens. But the knowledge of respiratory deposition is important also for occupational safety or targeted delivery of inhaled pharmaceuticals. Simulations utilizing computational fluid dynamics are becoming available to a wide spectrum of users and they can undoubtedly bring detailed predictions of regional deposition of particles. However, if those simulations are to be trusted, they must be validated by experimental data. This article presents simulations and experiments performed on a geometry of airways which is available to other users and thus those results can be used for intercomparison between different research groups. In particular, three hypotheses were tested. First: Oral breathing and combined breathing are equivalent in terms of particle deposition in TB airways, as the pressure resistance of the nasal cavity is so high that the inhaled aerosol flows mostly through the oral cavity in both cases. Second: The influence of the inhalation route (nasal, oral or combined) on the regional distribution of the deposited particles downstream of the trachea is negligible. Third: Simulations can accurately and credibly predict deposition hotspots. The maximum spatial resolution of predicted deposition achievable by current methods was searched for. The simulations were performed using large-eddy simulation, the flow measurements were done by laser Doppler anemometry and the deposition has been measured by positron emission tomography in a realistic replica of human airways. Limitations and sources of uncertainties of the experimental methods were identified. The results confirmed that the high-pressure resistance of the nasal cavity leads to practically identical velocity profiles, even above the glottis for the mouth, and combined mouth and nose breathing. The distribution of deposited particles downstream of the trachea was not influenced by the inhalation route. The carina of the first bifurcation was not among the main deposition hotspots regardless of the inhalation route or flow rate. On the other hand, the deposition hotspots were identified by both CFD and experiments in the second bifurcation in both lungs, and to a lesser extent also in both the third bifurcations in the left lung., Highlights • Limits of current methods in prediction of flow and high-resolution deposition in an airway geometry were investigated. • Experiments and simulations performed on a replica of airways - nasal and oral cavity and seven generations of TB branching. • The influence of the inhalation route on the flow field was negligible downstream of the glottis. • The carina of the first bifurcation was not among the main deposition hotspots regardless of the inhalation route. • Deposition hotspots identified in the second bifurcation in both lungs, and in both third bifurcations in the left lung.

Heat exchangers are multi-benefit thermal-devices, of wide use, as their structure varies with their scope of application. The development of channel configurations contained in these exchangers, and evaluation of their performance is the goal of many recent numerical and experimental achievements. Because of the high cost of such devices, many researchers had to follow CFD based computational methods instead of using experimental techniques. In this study, the hydrothermal structure of a finned channel heat exchanger is evaluated using the finite-volume based Ansys Fluent. Due to the complex structure of these channels, which contain overlapping transverse vortex generators, the flow develops into a turbulent structure that strongly influences the enhanced heat transfer. In this sense, various turbulence models are simulated to assess their numerical effect on the performance of the exchanger. Five different models are under experimentation which are (i) standard-, (ii) RNG- and (iii) realizable-case k-ε type models as well as (iv) standard- and (v) SST-case k-ω type models. As highlighted, the highest performance is reached with the SST-type k-ω, while the lowest one is that with the realizable-type k-ԑ.

We address the task of modelling numerically turbulent flows within random arrays of circular cylinders, relevant for several industrial and environmental applications. Numerical simulations are employed to model infinite domains of randomly placed emergent and rigid cylinders validated by a laboratory database acquired by a PIV system. The main goals are: (i) to discuss the effect of the numerical domain size and the grid resolution on the first and second order moments and (ii) to characterise the spatial distribution of mean flow and turbulence variables in the drag-wake controlled stratum. Five domains of different sizes (9–44 cylinders) and four grid resolutions were independently tested. The results show that the time-averaged velocity field and the Reynolds stress tensor were not significantly affected by the size of the tested numerical domains. The analysis of the grid resolution influence shows how the results improve with mesh refinement, while none of the tested meshes produces un-physical results. The present work provides guidance on the acceptable compromises, in terms of mesh resolution and domain size, when predicting, with eddy resolving computational fluid mechanics tools, first and second-order moments of turbulent flows within infinite arrays or randomly placed cylinders. © 2018 Elsevier Ltd 80 245 261 245-261

We evaluate here three hemodynamic models used for the numerical simulation of bare and stented artery flows. We focus on two flow features responsible for intra-stent restenosis: the wall shear stress and the re-circulation lengths around a stent. The studied models are the Poiseuille profile, the simplified pulsatile profile and the complete pulsatile profile based on the analysis of Womersley. The flow rate of blood in a human left coronary artery is considered to compute the velocity profiles. “Ansys Fluent 14.5” is used to solve the Navier–Stokes and continuity equations. As expected our results show that the Poiseuille profile is questionable to simulate the complex flow dynamics involved in intra-stent restenosis. Both pulsatile models give similar results close to the strut but diverge far from it. However, the computational time for the complete pulsatile model is five times that of the simplified pulsatile model. Considering the additional “cost” for the complete model, we recommend using the simplified pulsatile model for future intra-stent flow simulations.

This study developed a leakage model of flammable refrigerants in a building air-conditioning system, where the influencing factors of combustible gas distribution are considered including leakage rate, ventilation rate and room size. Propane is selected as refrigerant to study the effects of influencing factors on propane distribution in the room after leakage. The following conclusions are made: 1) increase of leakage rate changes the time when the ratio of dangerous area volume (RODAV) reaches 30% and the lasting time for RODAV exceeds 30%; RODAV is maintained below 30% if the leakage rate is not larger than 2.84 g/s; 2) no apparent effect of room size on concentration distribution was observed; 3) ventilation rate affects the RODAV level and propane distribution in the room, i.e. increase of ventilation rate will reduce the RODAV level and then the hazard in the building. © 2013 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the Asia-Oceania Association for Fire Science and Technology.

International audience; 1D-2D coupling for river ow modeling. A shallow water-based model for river-oodplain interaction (SW12D for Shallow Water 1D-2D) is presented. The main channel and oodplain are discretized using 1D and 2D elements respectively. The proposed model provides an improved description of hydraulic phenomena over existing models by (i) including lateral momentum transfer between the main channel and the oodplain, (ii) taking the 2D nature of the ow into account within the 1D elements that describe the main channel. This allows for a better description of phenomena such as head losses due to channel bends and meanders, and meander shortcuts during oods. To cite this article: P. Finaud-Guyot, C. Delenne, V. Guinot, C. Llovel, C. R. Mecanique 333 (2005). Résumé Couplage 1D-2D pour la modélisation des inondations uviales. Un modèle basé sur les équations de Saint-Venant en eau peu profonde (SW12D pour Shallow Water 1D-2D) est présenté. Le lit mineur et le lit majeur sont discrétisés avec des mailles 1D et 2D respectivement. Le modèle proposé apporte une meilleure description (en comparaison aux modèles existants) des phénomènes hydrauliques en (i) incluant un transfert de quantité de mouvement latérale entre les lits mineur et majeur, (ii) prenant en compte la nature 2D des écoulements dans les mailles 1D qui représentent le lit mineur. Cela permet une meilleure description des phénomènes tels que les pertes de charge dues aux coudes et méandres et tels que les court-circuits de meandres pendant les inondations. Pour citer cet article : P. Finaud-Guyot, C. Delenne, V. Guinot, C. Llovel, C. R. Mecanique 333 (2005). Version française abrégée ves —ppro™hes unidimensionnelles ont prouvé leur e0™—™ité d—ns l— modélis—tion des é™oulements)uE vi—uxD t—nt que ™euxE™i restent glo˜—lement —lignés —ve™ l9—xe du ™ours d9e—uF vors de ™ruesD ™ette —pE proxim—tion ne peut génér—lement plus être f—ite et des modèles à ™—siers ou en deux dimensions sont utilisésF gepend—ntD d—ns le premier ™—sD les tr—nsferts de qu—ntité de mouvementD essentiels à l— ˜onne représent—tion des phénomènes tels que les ™ourtE™ir™uits de mé—ndresD sont négligésF in deux dimensionsD un m—ill—ge pré™is du lit de l— rivière est né™ess—ire pour ™orre™tement prendre en ™ompte l— topogr—phieF ve m—ill—ge pro™he du lit de l— rivière doit don™ ég—lement être ™omposé de ™ellules de t—ille réduite et le p—s de temps de simul—tion doit être réduit en ™onséquen™e pour —ssurer l— st—˜ilité du s™hém— numériqueF …ne —ppro™he —ltern—tive ™onsiste à ™oupler les modèles Ih et PhF gepend—ntD les ™oupl—ges exist—nts ne sont génér—lement p—s s—tisf—is—ntsD puisque seuls les tr—nsferts de m—sse sont pris en ™ompte néglige—nt ™eux de qu—ntité de mouvementF h—ns l9—ppro™he proposéeD le ™oupl—ge est ré—lisé en in™lu—nt le modèle Ih d—ns un modèle Ph X ™h—que m—ille Ih du lit mineur de l— rivière est intégrée d—ns une m—ille Ph de l— pl—ine d9inond—tionF ge form—lisme permet une rédu™tion import—nte du nom˜re de m—illes en ™omp—r—ison d9un m—ill—ge ™l—ssique PhD et p—r ™onséquentD une rédu™tion du temps de ™—l™ulF ves équ—tions de ƒ—intE†en—ntD ét—˜lies pour ™h—que modèleD sont modi(ées pour prendre en ™ompte les tr—nsferts de m—sse et de qu—ntité de mouvement entre les modèlesF v— représent—tion des pertes de ™h—rges liées à l— sinuosité du ™ours d9e—u —insi que des phénomènes de ™ourtE™ir™uit de mé—ndres est —lors possi˜leF €lusieurs séries de mesures expériment—les ont été ré—lisées et ™omp—rées —ux résult—ts issus de l— simul—tion numérique —ve™ le ™ode ™ouplé IhEPh @ƒ‡IPhA et un ™ode Ph ™l—ssique @ƒ‡PhAF ves résult—ts produits p—r ƒ‡IPh sont plus en —déqu—tion —ve™ les mesures que ™eux de ƒ‡PhF in outreD les temps de ™—l™ul sont réduits d9un f—™teur IDS à VH selon les ™on(gur—tions simuléesF

In the case of multifluid flows, it is classical to refine the mesh in order to improve the precision. As mesh refinement criterion, we propose to use the numerical entropy production. In a refinement procedure by bitree, we check the relevance of this criterion. Our objective is to validate the mesh refinement before integrating it into a three-dimensional parallel code. To cite this article: F. Golay, C. R. Mecanique 337 (2009).

An extension of a slightly compressible flow model to double-diffusive convection of a binary mixture of ideal gases enclosed in a cavity is presented. The problem formulation is based on a low Mach number approximation and the impermeable surface assumption is not invoked. The main objectives of this paper are the statement of a new problem formulation, and the analysis of some significant results showing the influence of density variations on transient solutions for pure thermal or pure solutal convection. At steady-state, it is shown that the heat and mass transfer analogy may be applied for non-dilute mixtures at parameter ranges larger than those usually considered. To cite this article: H. Sun, G. Lauriat, C. R. Mecanique 337 (2009).

We examine the linear stability of a liquid layer heated from below (the classical Rayleigh–Benard problem) but laterally confined between four vertical rigid and adiabatic boundaries. The main feature of the present study is that the height of the layer is much greater than the two other horizontal dimensions. The Soret effect is also taken into account. The ultimate objective of the study is a better knowledge of the operation of thermogravitational columns, and the search for a possible new way to measure positive Soret coefficients based on the variation of the critical Rayleigh number. To cite this article: J.K. Platten et al., C. R. Mecanique 335 (2007).

International audience; A simple model for two-dimensional cavity flows is presented. It is based upon the Logvinovich independence principle. Each section of the cavity is assumed to behave independently of the neighbouring ones. The equation of evolution of the cavity interface is derived. It mainly takes into account an added mass effect and is similar to the well-known Rayleigh–Plesset equation relative to spherical bubbles. The dynamics of the 2D cavity is controlled by the pressure difference between infinity and the cavity. The model proves to be in good agreement with Tulin's solution for a steady cavity flow and easily applicable to unsteady cavity flows.; Une modélisation simple des écoulements cavitants bidimensionnels est proposée. Elle est basée sur le principe d'indépendance de Logvinovich qui suppose que chaque section de cavité se comporte indépendamment des voisines. L'équation d'évolution de l'interface est présentée dans cette Note. Elle prend essentiellement en compte un effet de masse ajoutée et est comparable à l'équation de Rayleigh-Plesset qui régit l'évolution d'une bulle sphérique. La dynamique d'une cavité bidimensionnelle est contrôlée par la différence entre la pression de cavité et la pression à l'infini. Le modèle est en bon accord avec la solution de Tulin pour un écoulement supercavitant stationnaire et est facilement applicable à une configuration instationnaire.