Modélisation et simulation numérique des échanges convectifs entre un écoulement diphasique incompressible et une surface chauffée

Compte tenu des importants transferts de chaleur qu'ils induisent, les procédés de refroidissement par des écoulements diphasiques (air/huile) sont utilisés pour le refroidissement des pistons moteur. La modélisation de ce procédé se fera à l'aide du modèle 1-Fluide diphasique couplé à l'équation de la chaleur. Des études expérimentales et numériques de jets liquides impactant sur des surfaces chauffées seront présentées. Les échanges convectifs liés à l'effet shaker présent dans les galeries de refroidissement des pistons automobiles seront également abordés

A model for single asperity perturbation on lubricated sliding contact with DLC-coated solids

International audienceIn lubricated sliding contact systems with DLC coated solids, recent studies have shown that DLC coatings are highly sensitive to asperities breaking through the lubricant film within the contact area. Those asperities produce damages similar to those obtained from scratch tests, from where coating delamination can initiate and propagate. To better understand the link between scratches and coating delamination, endurance tests can then be performed on coating with controlled initial scratches. To ensure the scratches’ representativity with respect to the actual asperities’ contact condition, one has to estimate the load transmitted by such asperities as well as the induced perturbation on surface and subsurface stresses. In this paper, a simplified numerical model corresponding to such problems is presented. It is consistent with elasto-hydrodynamic (EHD) lubrication approximations and can be used on coated or uncoated systems. As a simplified model, it can be run quickly on multiple configurations, enabling the creation of representative scratch maps for the given lubricated contact conditions

Mechanical behavior of DLC coatings under various scratch conditions

International audienceIn lubricated sliding contact systems with Diamond-Like Carbon (DLC) coated solids, several studies have shown DLC coatings are highly sensitive to asperities breaking through the lubricant film within the contact area. Those asperities produce damages similar to those obtain from scratch tests, from where coating delamination can initiate and propagate. In the present study, controlled scratches have been performed on DLC-coated samples by varying the tip radius, the normal load and the sliding speed. From one hand, the different fracture mechanisms are compared to those observed on a coated cam-tappet system. They both lead to similar damage and wear, from substrate plasticity to gross spallation, via tensile and angular cracking. On the other hand, a numerical analysis is conducted with a finite element model. It reveals the fracture mechanism can be qualitatively predicted. Additional computations show the scratch severity increases by considering a thinner coating. This upholds the observed experimental coupling between tribochemical wear, scratch networks and coating delamination

Influence of scratches on the wear behavior of DLC coatings

International audienceIn lubricated sliding contact systems with Diamond-Like Carbon (DLC) coated solids, several studies have shown that DLC coatings are highly sensitive to asperities breaking through the lubricant film within the contact area. Those asperities produce damages similar to those obtain from scratch tests, from where coating delamination can initiate and propagate. In this work, the influence of initial surface degradations upon the coating lifetime is investigated using wear tests on initially scratched DLC coatings. Results shown that although scratches can be seen as initial damage leading to local spalling, they are likely to break the most prominent roughness peaks of the counterbody and, as a result, to protect the overall coated surface from excessive contact pressure and increase the overall coating lifetim

Optimal Design of High-Speed Electric Machines for Electric Vehicles: A Case Study of 100 kW V-Shaped Interior PMSM

The need of compact machines increased in recent years due to increases in raw materials’ price. Hence, many studies are currently being conducted on high-speed challenges to propose an optimal design methodology. AC losses in windings are often not included in the optimization process and are treated in post-processing by choosing a suitable conductor’s diameter to mitigate skin and proximity effects. This paper presents an optimization and design methodology for high-speed electric machines considering these losses, using models with an interesting trade-off between computation time and accuracy, which is helpful for large-scale optimization, in which more than 9,600,000 machines are evaluated. Optimizations are conducted on 100 kW high-speed one-layer V-shaped interior permanent magnet synchronous machines, widely used in vehicles thanks to their high power density, based on the specifications of the Peugeot e208, for different values of pole pairs and maximum speed. The influence of lamination thickness, fill factor, and maximum current density on the optimal design is also investigated. This paper concludes the utility of increasing speed to achieve high power density and proposes best alternatives regarding automotive constraints. Results show that the number of pole pairs is not always a key parameter in obtaining the lowest volume, especially at high speed

Hybrid model for AC Losses in High Speed PMSM for arbitrary flux density waveforms

International audienceIncreasing speed of electric machine leads to high losses especially in stator winding assembly due to eddy currents effect. Commonly adopted formula for AC losses calculation tends to be applicable in the case of sinusoidal flux density. In this paper, a hybrid model predicting AC winding loss is presented based on one slot per pole of surface-mounted permanent-magnet machines using two formula taking into account the true flux density waveform. The results obtained comply with finite-elements results. The hybrid model was also used to investigate the influence of tooth-tip on AC losses

AC Losses in Windings: Review and Comparison of Models with Application in Electric Machines

Industry is increasingly adopting high-speed electric machines due to their high-power density and low cost. However, increasing the speed leads to many challenges that are worth to study since they have relevant impact on the design of the machine. One of these challenges is the losses in stator winding assembly. At low frequency, losses in windings are usually assumed equal to DC losses. However, at high frequency some phenomena become noticeable and worth evaluating since they lead to noticeable losses. AC losses in windings are due to skin effect, proximity effect, and circulating currents. The main models of AC losses in windings in the literature are presented for both circular and rectangular wires. These models are compared using both interior and surface-mounted permanent magnet synchronous machines. Results show that for proximity effect, analytical model is convenient when considering armature reaction only, however, when considering on load case, hybrid model with simple FEA is suitable thanks to its interesting trade-off between accuracy and computation time, which makes it suitable for large-scale optimization. For circulating currents effect, finite element model is unavoidable. Moreover, two important properties concerning circulating currents are stated as well as their mathematical proofs.Peer reviewe