# Numerical and Experimental Analysis of the Oil Flow in a Planetary Gearbox
## 4 Conclusions  
In the present work, a planetary gearbox was analyzed with a combined experimental-numerical approach. A transparent housing cover allowed recording of the oil flow in the front part of the gearbox by a high-speed camera. This allowed to capture the oil flow characteristics that typically originate in planetary gearboxes. The current analysis proposes a new remeshing approach that is on the one hand based on the proper partitioning of the computational domain to obtain an extruded mesh and, on the other hand, based on an innovative mesh-handling strategy that exploits a pre-computed set of mesh for the whole simulation. The implemented approach allowed running of such simulations on only four cores without the need for a computer cluster. The simulation results are in good agreement with the experimental observations, despite some discrepancies at the centerline immersion depth, where the oil remained stitched on the planet carrier in the simulations and did not flow down. The simulations at lower immersion depth could be compared  
Figure 14: (**A–F**) evolution of the oil flow for the SIM-id2v3 operating condition at different timesteps during the planet carrier rotation. The oil is gradually brought to the other parts of the gearbox. The contact between the planets and the ring gears seems to be well lubricated. The rotatory motion of the oil flow gives origin to oil rings around the planet carrier and the planets.  
Figure 13: Pressure contour on the wheels.  
with [PERSON] et al. [2]. The oil flow prediction in the front part of the gearbox is similar to the one predicted in their work. However, a different level of detail can introduce some differences in the oil flow.  
The current work allowed a good understanding of the oil flow characteristics in the considered planetary gearbox: at low speeds, oil rings originate because the oil remains in contact with the rotating parts and this phenomenon promotes circular oil tracks; at high speeds, the oil is mainly splashed towards the housing due to the high centrifugal effects and forms a ring around the housing walls. These observations refer to the investigated immersion depths. These phenomena have also been observed by [PERSON] et al. [2] in their analysis at different immersion depths and oil viscosities.  
The numerical studies on planetary gears available in the literature are mostly not validated so far. In this study, for the first time, experimental observations and CFD modeling were successfully combined to evaluate the numerical approach used to predict oil distribution and contribute to a better understanding of oil flow in planetary gears.  
M.N.M.: conceptualization, methodology, software, validation, formal analysis, investigation, resources, data curation, writing--original draft, writing--review and editing, visualization. L.H.: validation, investigation, writing--review and editing. C.P.: conceptualization, validation, investigation, writing--review and editing. T.L.: conceptualization, writing--review and editing, supervision, project administration. K.S.: writing--review and editing, resources. F.C.: conceptualization, methodology, software, validation, formal analysis, investigation, resources, data curation, writing--original draft, writing--review and editing, visualization, supervision. All authors have read and agreed to the published version of the manuscript.  
The publication of this work is supported by the Open Access Publishing Fund of the Free University of Bozen/Bolzano.  
Not applicable.  
The data that support the findings of this study are available from the corresponding author (F.C.) upon reasonable request.  
The authors would like to thank [PERSON] and [PERSON] from Comer Industries for sharing the experimental data.  
The authors declare no conflict of interest.