Gearboxes are integral machine components that determine the capability and reliability of many aerospace and automobile industry systems. Continuous demand for higher efficiency and reliability, increased load-carrying capacity and endurance life, smaller size, lower weight, lower noise and vibrations, prolonged service intervals and low costs are the main driving forces in the development of gear drives in the future. For many gearboxes, the thermo-fluids of the gas/oil/solid system determine the gearbox performance and its durability and life. However, there is a very limited predictive capability of the thermo-fluid characteristics of gearbox due, in large part, to its excessive complexity.

In this paper, we present a coupled thermo-fluid model for the simulation of the two-phase flow along with the heat transfer within gearbox systems in a conjugate fashion. The primary challenge is the enormous separation of fluid-mechanics and heat-transfer time-scales which makes the conventional way of solving the coupled thermo-fluid system of equations computationally prohibitive. In contrast, the approximate approach developed in this study exploits this separation of scales to provide an accurate representation of the long-term, time dependent thermo-fluid state of the gearbox at a modest computational cost. The commercial package ANSYS FLUENT is used to solve URANS equations for fluid mechanics and VOF for the two-phase interface capturing, while the energy equation is modified through user-defined functions to solve for the temperature field inside the fluid and solid components. In addition, the heat generation raised by the meshing of the gears is provided by a separate model based on gear geometry and operating conditions. The approach is verified against a full-fidelity simulation for a simplified and accelerated gear system and is validated against experiments.

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