Yann Marchesse

Investigations on CFD Simulations for Predicting Windage Power Losses in Spur Gears

In this paper, a computational fluid dynamics (CFD) code is applied to two- and three-dimensional simulations of windage power loss generated by spur gears rotating in air. Emphasis is placed on the various meshes associated with the finite volume method and on the choice of turbulence model. Comparing CFD predictions with the power losses measured on a specific test rig, it is shown that the fluid ejection in the radial direction must be included in order to reproduce the experimental evidence. The relative importance of the losses generated by the gear front and rear faces along with those due to the teeth is discussed. The volumetric flow rate expelled by the teeth is analyzed and the influence of flanges is highlighted.

Numerical Investigations on Drag Coefficient of Balls in Rolling Element Bearing

In high-speed rolling element bearings the drag force generated by the motion of the balls in an air–oil mixture is frequently taken into account using the results for a sphere in an infinite medium. This approach is surprising because important interaction between the flows around the balls may occur. The drag coefficient value should be then adjusted to the configuration that is observed in a rolling element bearing (REB). In this article, a computational fluid dynamics code is applied to simulate three configurations: one single sphere, two spheres in tandem, and a set of spheres that are aligned along the air flow. It can be seen that both the flow pattern around one sphere and its drag coefficient are modified when placing another sphere in its vicinity. Furthermore, in REB configuration the drag coefficient value is far from the one observed when the obstacle is isolated and mainly depends on the space between the obstacles.

Comparison between a generalized Newtonian model and a network-type multiscale model for hemodynamic behavior in the aortic arch: Validation with 4D MRI data for a case study

Blood is a complex fluid in which the presence of the various constituents leads to significant changes in its rheological properties. Thus, an appropriate non-Newtonian model is advisable; and we choose a Modified version of the rheological model of Phan-Thien and Tanner (MPTT). The different parameters of this model, derived from the rheology of polymers, allow characterization of the non-Newtonian nature of blood, taking into account the behavior of red blood cells in plasma. Using the MPTT model that we implemented in the open access software OpenFOAM, numerical simulations have been performed on blood flow in the thoracic aorta for a healthy patient. We started from a patient-specific model which was constructed from medical images. Exiting flow boundary conditions have been developped, based on a 3-element Windkessel model to approximate physiological conditions. The parameters of the Windkessel model were calibrated with in vivo measurements of flow rate and pressure. The influence of the selected viscosity of red blood cells on the flow and wall shear stress (WSS) was investigated. Results obtained from this model were compared to those of the Newtonian model, and to those of a generalized Newtonian model, as well as to in vivo dynamic data from 4D MRI during a cardiac cycle. Upon evaluating the results, the MPTT model shows better agreement with the MRI data during the systolic and diastolic phases than the Newtonian or generalized Newtonian model, which confirms our interest in using a complex viscoelastic model.

Preliminary numerical investigations on windage power losses generated by helical gears

This paper investigates the windage power loss generated by helical gears rotating in pure air. A three-dimensional approach using computational fluid dynamics (CFD) code which has been validated for spur gear is adapted here in order to consider helix angle. The numerical approach is at first validated with the power losses measured in similar conditions. The influence of both width and helix angle values on the expelled volumetric flow rate and the windage losses are studied. Considering these observations, a correlation which is based on a classical approach used in turbomachinery is proposed.

On the influence of helix angle and face width on gear windage losses

This paper investigates the windage power losses generated by helical gears rotating in pure air based on experimental results and a computational fluid dynamic code. It is found that the simulated flow patterns are totally different from those calculated for spur gears and that both tooth face width and helix angle are influential. The windage losses derived from Dawson’s and Townsend’s formulae are critically assessed using computational fluid dynamic results thus highlighting the limits of a unique formulation for accurate windage loss prediction. Finally, an analytical approach is suggested which gives good results providing that the flow rates at the boundaries of the inter-tooth domains can be estimated.