Experimental and Numerical Investigation of Dispersed and Continuous Liquid Film under Boiling conditions

[EN] In this work, both experimental and numerical investigations have been carried out in order to improve the modelling of the vaporization of wall liquid-deposits in internal combustion engines. A comprehensive model is suggested for the vaporization of liquid films in the different boiling regimes, including nucleate boiling regime, the Leidenfrost boiling regime, as well as the transition boiling regime occurring between the two latter. This work extends the validity of the Liquid Film Boiling model (Habchi, Oil & Gas Science and Technology – Rev. IFP, Vol. 65, No. 2, 2010) for dispersed liquid films that may be formed when a dilute spray impinges a wall. A sub-grid liquid film is indeed considered when the wetted-area is smaller than the wall cell-face area. A sessile droplet model is used to estimate the wall area wetted by the liquid film and whether it is resolved by the grid or located in the sub-grid scale (SGS). In addition, a novel Leidenfrost vaporization model is proposed for spray droplets located near a hot wall. The above vaporisation/boiling models has been implemented in the Large-Eddy simulation (LES) AVBP code. The validation has been carried out using two different experiments. First, the experimental lifetime curve of a sessile droplet (Stanglmaier et al., SAE paper 2002-01-0838) has been used for a quantitative validation in the different boiling regimes. Second, the wall impingement of a heptane spray from a typical gasoline injector from Continental Automotive, has been simulated. The numerical results obtained under boiling conditions, are compared to the liquid film footprints and lifetime provided by the Refractive Index Matching (RIM) experiment which is described in this article.Habchi, C.; Lamarque, N.; Helie, J.; Jay, S. (2017). Experimental and Numerical Investigation of Dispersed and Continuous Liquid Film under Boiling conditions. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 921-928. https://doi.org/10.4995/ILASS2017.2017.4632OCS92192

Regional identification of mechanical properties in arteries

International audienceAortic aneurysms are often characterized by localized changes in aortic wall composition and structure that result from the degradation of elastin, loss of smooth muscle cell function, and remodeling of collagen. Correlations between wall composition and local mechanical properties can potentially provide insight into conditions that render a vessel susceptible to failure. Previous work has shown that chronic angiotensin-II infusion in ApoE-/- mice often results in dissecting aneurysms (Bersi et al. 2012). The objective of this work is to establish a new protocol able to characterize in vitro the local mechanical properties of arteries on the murine model

Large-eddy simulation analysis of knock in a direct injection spark ignition engine

International audienceDownsized spark ignition (SI) engines running under high loads have become more and more attractive for car manufacturers because of their increased thermal efficiency and lower CO2 emissions. However, the occurrence of abnormal combustions promoted by the thermodynamic conditions encountered in such engines limits their practical operating range, especially in high efficiency and low fuel consumption regions. One of the main abnormal combustion is knock, which corresponds to an autoignition of end gases during the flame propagation initiated by the spark plug. Knock generates pressure waves which can have long term damages on the engine, that is why the aim for car manufacturers is to better understand and predict knock appearance. However an experimental study of such recurrent but non-cyclic phenomena is very complex, and these difficulties motivate the use of CFD for better understanding them. In the present paper, Large-Eddy Simulation (LES) is used as it is able to represent the instantaneous engine behavior and thus to quantitatively capture cyclic variability and knock. The proposed study focuses on the LES analysis of knock for a direct injection SI engine. A spark timing sweep available in the experimental database is simulated, and 15 LES cycles were performed for each spark timing. Wall temperatures, which are a first order parameter for knock prediction, are obtained using a conjugate heat transfer study. Present work points out that LES is able to describe the in-cylinder pressure envelope whatever the spark timing, even if the sample of LES cycles is limited compared to the 500 cycles recorded in the engine test bench. The influence of direct injection and equivalence ratio stratifications on combustion is also analyzed. Finally, focusing on knock, a MAPO (Maximum Amplitude Pressure Oscillation) analysis is conducted for both experimental and numerical pressure traces pointing out that LES well reproduces experimental knock tendencies

Lattice-Boltzmann simulations of traffic-related atmospheric pollutant dispersion in urban areas

The developing field of urban physics includes computational fluid dynamics (CFD) as a tool to model wind comfort, heat management and pollutant dispersion in cities. In particular, road traffic emissions significantly contribute to air pollution and should be considered in atmospheric dispersion simulations. To this end, the lattice-Boltzmann method (LBM) offers a promising alternative to traditional finite-volume CFD solvers in terms of computational cost and accuracy. At IFP Energies Nouvelles (IFPEN), a recent emission model relying on real-life driving data recorded with a mobile application was used to construct urban emission maps. However, it has not been coupled yet with a precise unsteady CFD solver, which could provide local unsteady and accurate information about local concentration fields. We propose to combine the LBM open-source code OpenLB with the emission model designed at IFPEN to simulate traffic-induced pollutant dispersion in an urban-like environment. The LBM code is used to solve the Navier-Stokes equations as well as the passive scalar transport with a double distribution function (DDF) approach. The solver is successfully validated on the well-known CODASC test case and a first evaluation of the impact of a representative urban setting on pollutant dispersion with non-uniform sources is proposed

Modélisation du comportement mécanique d’artères carotides communes humaines in vivo

A partir de mesures non invasives cliniques sur des sujets humains, nous proposons un nouveau modèle de comportement mécanique 3D d'artères carotides communes qui tient compte du caractère hyperélastique, composite, actif, précontraint et dynamique du tissu biologique. Le problème aux limites est résolu par une méthode semi-analytique, ce qui permet d’obtenir une évaluation des cinématiques de déformation et des distributions de contraintes pariétales de la structure artérielle in vivo au cours d’un cycle cardiaque

Interpreting Deep Learning-Based Networking Systems

While many deep learning (DL)-based networking systems have demonstrated superior performance, the underlying Deep Neural Networks (DNNs) remain blackboxes and stay uninterpretable for network operators. The lack of interpretability makes DL-based networking systems prohibitive to deploy in practice. In this paper, we propose Metis, a framework that provides interpretability for two general categories of networking problems spanning local and global control. Accordingly, Metis introduces two different interpretation methods based on decision tree and hypergraph, where it converts DNN policies to interpretable rule-based controllers and highlight critical components based on analysis over hypergraph. We evaluate Metis over several state-of-the-art DL-based networking systems and show that Metis provides human-readable interpretations while preserving nearly no degradation in performance. We further present four concrete use cases of Metis, showcasing how Metis helps network operators to design, debug, deploy, and ad-hoc adjust DL-based networking systems.Comment: To appear at ACM SIGCOMM 202

Combining landscape genomics and ecological modelling to investigate local adaptation of indigenous Ugandan cattle to East Coast fever

East Coast fever (ECF) is a fatal sickness affecting cattle populations of eastern, central, and southern Africa. The disease is transmitted by the tick Rhipicephalus appendiculatus, and caused by the protozoan Theileria parva parva, which invades host lymphocytes and promotes their clonal expansion. Importantly, indigenous cattle show tolerance to infection in ECF-endemically stable areas. Here, the putative genetic bases underlying ECF-tolerance were investigated using molecular data and epidemiological information from 823 indigenous cattle from Uganda. Vector distribution and host infection risk were estimated over the study area and subsequently tested as triggers of local adaptation by means of landscape genomics analysis. We identified 41 and seven candidate adaptive loci for tick resistance and infection tolerance, respectively. Among the genes associated with the candidate adaptive loci are PRKG1 and SLA2. PRKG1 was already described as associated with tick resistance in indigenous South African cattle, due to its role into inflammatory response. SLA2 is part of the regulatory pathways involved into lymphocytes' proliferation. Additionally, local ancestry analysis suggested the zebuine origin of the genomic region candidate for tick resistance

Development and application of bivariate 2D-EMD for the analysis of instantaneous flow structures and cycle-to-cycle variations of in-cylinder flow

International audienceThe bivariate two dimensional empirical mode decomposition (Bivariate 2D-EMD) is extended to estimate the turbulent fluctuations and to identify cycle-to-cycle variations (CCV) of in-cylinder flow. The Bivariate 2D-EMD is an adaptive approach that is not restricted by statistical convergence criterion, hence it can be used for analyzing the nonlinear and non-stationary phenomena. The methodology is applied to a high-speed PIV dataset that measures the velocity field within the tumble symmetry plane of an optically accessible engine. The instantaneous velocity field is decomposed into a finite number of 2D spatial modes. Based on energy considerations, the in-cylinder flow large-scale organized motion is separated from turbulent fluctuations. This study is focused on the second half of the compression stroke. For most of the cycles, the maximum of turbulent fluctuations is located between 50 and 30 crank angle degrees before top dead center (TDC). In regards to the phase-averaged velocity field, the contribution of CCV to the fluctuating kinetic energy is approximately 55% near TDC

TOI-4010: A System of Three Large Short-Period Planets With a Massive Long-Period Companion

We report the confirmation of three exoplanets transiting TOI-4010 (TIC-352682207), a metal-rich K dwarf observed by TESS in Sectors 24, 25, 52, and 58. We confirm these planets with HARPS-N radial velocity observations and measure their masses with 8 - 12% precision. TOI-4010 b is a sub-Neptune ($P = 1.3$ days, $R_{p} = 3.02_{-0.08}^{+0.08}~R_{\oplus}$, $M_{p} = 11.00_{-1.27}^{+1.29}~M_{\oplus}$) in the hot Neptune desert, and is one of the few such planets with known companions. Meanwhile, TOI-4010 c ($P = 5.4$ days, $R_{p} = 5.93_{-0.12}^{+0.11}~R_{\oplus}$, $M_{p} = 20.31_{-2.11}^{+2.13}~M_{\oplus}$) and TOI-4010 d ($P = 14.7$ days, $R_{p} = 6.18_{-0.14}^{+0.15}~R_{\oplus}$, $M_{p} = 38.15_{-3.22}^{+3.27}~M_{\oplus}$) are similarly-sized sub-Saturns on short-period orbits. Radial velocity observations also reveal a super-Jupiter-mass companion called TOI-4010 e in a long-period, eccentric orbit ($P \sim 762$ days and $e \sim 0.26$ based on available observations). TOI-4010 is one of the few systems with multiple short-period sub-Saturns to be discovered so far.Comment: 26 pages, 16 figures, published in A