Validation of a Commercial Lagrangian CFD Solver for Gear Lubrication Simulations

Geared turbofan (GTF) technology is promising for reducing specific fuel consumption, jet noise, and engine emissions, making gearbox efficiency crucial. Power losses in gearboxes are either load-dependent (mechanical) or load-independent (fluid-dynamic), with the latter needing better modeling. This thesis investigates fluid-dynamic losses in gear lubrication for GTF engines, where lubrication is achieved through an oil jet impacting the gear teeth. In the literature, similar problems are studied through experiments and numerical simulations, primarily using Eulerian CFD solvers for their precision in describing physical behaviour at a microscopic level. Simulating an oil jet lubrication problem involves managing a multiphase system in a moving domain, which is computationally demanding with Eulerian CFD using the VOF method and moving mesh techniques. Lagrangian CFD solvers, though potentially less accurate, offer a less computationally intensive alternative. This thesis tests the commercial software Particleworks, based on the MPS method, to evaluate its effectiveness in simulating gear lubrication and establish best practices for its use, comparing the results with those from validated Eulerian CFD codes. The problem under analysis consists of a single rotating gear lubricated through a radial oil jet impacting on its teeth. The main phenomena of interest are: the oil jet breakup due to the induced airflow, the resistant torque induced by the oil jet impact on the teeth, the wetting behavior, which means the oil-gear interaction, and finally the impingement depth of the oil jet on the tooth flank. The torque affects the efficiency of the system, but the other aspects directly influence the lubrication effectiveness, which is of primary importance in reaching the prescribed lifetime of the gearbox. Initially, oil is considered in a single-phase system, with long and short-duration simulations conducted to analyze various phenomena. Long-duration simulations focus on the frequency spectrum of the output torque signal, while short-duration simulations examine the shape, values of the resistant torque, wetting behavior, and impingement depth. A sensitivity analysis is performed by varying particle size, sampling frequency, oil properties, gear roughness, and software settings. Subsequently, airflow is simulated as a single-phase system in Particleworks and then integrated into the previous simulations to create a multiphase system, enabling the study of oil jet breakup. Additional long and short-duration simulations assess the airflow's impact on the results. Comparing the results with the reference data shows that the Lagrangian software effectively models oil-gear interactions, even under extreme conditions (gear speeds above 12,000 rpm and oil jet velocities around 25 m/s), and does so with significantly shorter computational times than traditional Eulerian CFD. Although Particleworks slightly overestimates resistant torque values, the torque curve shapes align closely with expectations. The negligible effect of airflow simplifies simulations, reducing computational effort. Thus, despite its simplicity and potential inaccuracies, Particleworks proves to be a viable alternative to standard Eulerian CFD solvers for this specific application.