Publications

In this paper, a numerical investigation of the impact of asymmetric heating on laminar mixed convection in Poiseuille-Rayleigh-Bénard water flow within parallel horizontal channels is presented. The study has been carried out in a rectangular channel with a transverse aspect ratio of 10, and considered both low (Ra = 1.28 × 10^4) and high (Ra = 1.4 × 10^5) Rayleigh numbers, with Reynolds numbers of 50 and 100. A uniform heat flux was applied to the top and bottom walls of the heated region to assess its effect on the system's thermoconvective behavior and heat transfer efficiency. Two flux ratio scenarios were considered: qt/qb = 1 and qt/qb = 2. The results indicate that increasing the flux ratio intensifies the destabilizing temperature gradient and significantly enhances buoyancy-induced flow, thereby influencing the patterns of thermoconvective structures. Specifically, flux ratios lead to an increased number of plumes originating from the bottom of the channel, while reducing their height and confining them between the bottom wall and the upper thermal boundary layer. It is also observed that flux ratios do not affect the mechanisms involved in the formation of longitudinal rolls. Furthermore, at low Rayleigh numbers, asymmetric heating has a pronounced impact on the establishment length. In contrast, this effect diminishes and becomes negligible at higher Rayleigh numbers. Numerical computations further reveal that near the bottom wall, the Nusselt number exhibits singular behavior, approaching infinity. Regardless of Reynolds and Rayleigh numbers, flux ratios significantly enhance heat transfer within the system. Additionally, near the top wall, the buoyancy effects from the bottom wall have negligible impact on heat transfer, except in the case where qt/qb = 2, Re = 50 and Ra = 1.4 × 10^5, where instability in the upper thermal layer was observed.

This study investigates the evolution of structure and microstructure alongside thermomechanical properties of Ni80Co17Mo3 alloy powder mixture subjected to high-energy mechanical milling. Scanning electron microscopy observations reveal a consistent particle size reduction to 22 ± 2 μm. X-ray diffraction analysis confirms the formation of an FCC nanostructured solid solution NiCo(Mo) after 6h of milling, with a mean crystallite size ⁓ 56.4 nm and microstrain up to 6.5×10−3 % after 72 h. Thermogravimetric analysis manifests a precise mass gain trend, showing a strong correlation (R2 = 0.90–0.99) between milling time and compositional changes, with an average activation energy of 70.68 ± 3.5 kJ/mol supporting the thermodynamic modelling results. Due to structural and microstructural modifications associated with mechanical milling, the microhardness significantly increases from 134.00 to 285.00 HV. These findings highlight insights into optimizing nanostructured materials and provide a framework for designing advanced materials for water splitting and aerospace.

In this work we propose a very high-order compressible finite volume scheme with a posteriori stabilization for the computation of multi-component two-phase flow with phase change. It is based on finite volume approach using moving least squares (MLS) reproducing kernels for high order reconstruction of the Riemann states. Increased robustness is achieved by using the multi-dimensional optimal order detection (MOOD) method to get a high-accurate and low-dissipation scheme while maintaining boundedness and preventing numerical oscillations at interfaces and strong gradient zones. The properties of the proposed framework are demonstrated on classical test problems starting with convergence order verification on simple scalar advection test cases. More complex shock and more stringent tube tests with various water, steam and air concentration are then simulated and compared with available references in the literature. Finally, the ability of the proposed approach to compute multi-component flows with phase change is illustrated with the simulation of a liquid oxygen jet in gaseous hydrogen.

Thermal mixing fluids in chaotic microdevices have significant importance in many potential applications and have enormous utility in thermal engineering processes. In microfluidic devices, The Two-Layer with Crossing Channels Micromixer (TLCCM) emphasized its efficiency in thermally homogenizing Newtonian fluids, which inspired us to investigate its performance using pseudoplastic fluids. A numerical comparative investigation has been carried out to evaluate the thermal mixing performances of pseudoplastic fluids in laminar steady flows using four chaotic microdevices: TLCCM, L, OH and OX. Quantitative validation of pseudoplastic fluids within a complex geometry, subject to constant heat flux, has been done. Navier-Stokes, the mass conservation, energy and species transport equations have been solved numerically employing CFD code. The pseudoplastic fluids consist of carboxymethyl cellulose solutions, which are characterized using the power-law model, the flow behavior index ranging from 0.75 to 1 and the generalized Reynolds number ranging from 0.2 to 70. To quantify the thermal mixing efficiency, the effects of the fluid behavior index, the generalized Reynolds number, on the thermal mixing degree for the proposed micromixers are presented, where high thermal mixing degrees have been obtained which evolve between 0.9 and 0.99. The entropy generation due to heat transfers and fluid pressure drops has been introduced versus the generalized Reynolds numbers for different fluid behavior indexes. The Bejan number values evolve close to 1. The probability density function PDF (%) at the TLCCM micromixer exit is localized in a narrow range that refers to the ideal temperature value for mixing, which is 315 Kelvin, whatever the fluid behavior index value.

AbstractAccurate predictions concerning a forging process can be obtained by numerical simulation, but only with a thorough knowledge of the main process variables. The material flow behavior and the interface effects are already well studied in the literature, but not the machine behavior, although it is required to estimate blow efficiency and deduce the energy actually transmitted to the workpiece. In this paper, an experimental methodology was applied to determine a spring-mass-damping model and its associated parameters for a screw press. The model and its parameters were identified with press strikes performed without billet. For validation, simulations were performed to predict blows on copper billets. The model’s predictions were in good agreement with the experimental measurements for ten consecutive blows on a copper billet. The decrease of process efficiency and the evolution from inelastic blows to elastic blows were correctly depicted by the model.

Dans cet article, une approche en 4 étapes est proposée pour parvenir à une prédiction en temps réel des résultats d’opérations de forgeage. Tout d’abord, un modèle de substitution basé sur les données de simulations numériques est construit grâce à des réseaux de neurones artificiels. Ce modèle est capable de reproduire les caractéristiques clés du processus lié aux lopins avec une efficacité de calcul accrue. Ensuite, ce modèle est couplé à un modèle masse-ressort-amortisseur de la machine de forgeage et des outils afin de capturer les interactions dynamiques. Enfin, l’approche est validée en comparant les prédictions avec les résultats expérimentaux, ce qui permet de vérifier l’efficacité du modèle pour prédire les paramètres clés du processus de forgeage.

Climate change is driving new and more efficient ways of producing and storing energy. In particular, Lithium-ion batteries demonstrate to be a worthwhile storage system for their high specific power and energy density. Due to electrochemical processes inside batteries, high temperatures are achieved during fast charge and discharge. Herein, a novel jet-grid cooling technique, named ImpFilm, featuring fluid impingement and fluid film is proposed. The idea is to introduce an innovative system able to guarantee stable and uniform temperature for Lithium-ion batteries with the purpose to reduce weight and costs. Firstly, the system has been designed by means of a preliminary 0D thermodynamic analysis. Then, 3D CFD simulations have been run on a single module to test its feasibility and effectiveness by the standpoint of fluid and thermodynamics. Mass flow rate, velocity field, volume fraction and temperature distribution are analyzed in the module by focusing on the impact of the geometry grid on both flow dynamics and cell temperature evolution. Results show that a parametric study on the grid design is necessary to balance the flow rate subdivision and to uniform the temperature of all the batteries. Eventually, new grid features prove to be effective in keeping battery temperature uniform and below hazardous thresholds.

We consider the moving least squares method to solve compressible two‐phase water‐water vapor flow with surface tension. A diffuse interface model based on the Navier–Stokes and Korteweg equations is coupled with a suitable system of state equations that allows for a more realistic estimation of the pressure jump across the liquid–vapor interface as a function of temperature. We propose a simple formulation for computing the capillarity coefficient based on the surface tension and the thickness of the diffuse interface. A convergence analysis using pressure jump in the test case of static bubble is conducted to verify our solver. We present several numerical test cases that illustrate the ability of our model to reproduce qualitatively and quantitatively the effects of surface tension on cavitation bubbles in general situations.

The use of Virtual Machining models may be a valuable approach in the designing stage of a machining operation as long as the models are sufficiently accurate. When vibration risks are suspected, stability analysis approaches to predict regenerative chatter phenomena are generally used. However, although these approaches, when applicable, allow efficient numerical optimization of the process around an operating point, they often require other strong assumptions such as neglecting transient phenomena or oversimplifying kinematics. On the other hand, time domain approaches with detailed matter removal modelling allow to monitor the continuous evolution of cutting conditions and represent various phenomena that the models can reproduce (regenerative chatter, forced vibrations, non-linear behaviours). The amount of data produced is, however, considerable and often costly to analyse. It may therefore be interesting to deduce, from these data, scalar indicators allowing easier and more relevant analysis of the simulation results. In this work, the modal work of the cutting forces upon the workpiece vibratory displacements is proposed as an indicator to discriminate different tool paths. A one degree of freedom theoretical problem and a face milling operation on extruded aluminum profiles extracted from automotive structural part are used to explain and show the relevance of such indicator.

Pure BMI resin based on 4,4′-bismaleimidodiphenylmethane (BMI) and its copolymers with various quantities of 2,2′-diallylbisphenol A (BMI-DABPA 2–1, BMI-DABPA 1–1, BMI-DABPA 1–2) were thermally aged. Ageing at 160 °C was monitored by FTIR and showed the greatest reactivity of diallyl groups which accelerate the degradation of BMI-DABPA copolymers. It was confirmed by a gravimetric study of ageing under nitrogen or oxygen at 350 and 375 °C. A co-oxidation kinetic model was proposed for describing the oxidation of BMI and BMI-DABPA systems. The effect of the main kinetic parameters was discussed from a parametric study. The main rate constants were estimated from the fitting of experimental curves and comparable gravimetric data from literature.