CFD on Open Wet Cutch to Reduce Drag Losses

Abstract: As the need for highly efficient transmission systems increase, it is imperative to have lower fuel consumption levels. Hence, it becomes crucial to investigate and understand reasons behind various losses occurring within the system. Clutches and gears contribute to the major losses within a transmission system. In this thesis project, the drag losses in disengaged wet clutch is studied and efforts have been made to come up with solutions to reduce these losses. Computational Fluid Dynamics (CFD) is used as tool to understand the oil flow in the clutch system. The thesis tasks focused on: - Better understanding of flow physics and oil inlet to the clutch pack - Design and analysis of groove patterns to reduce drag loss - Understand the effect of rotation of clutch discs on groove functionality - Development of a multiphase CFD model with realistic boundary conditions for clutch analysis Initially, the entire clutch pack is modelled to study the oil flow and estimate the amount of oil that is being pumped into the individual gaps between the steel plates and friction discs. To analyze different groove patterns, the clutch model was simplified and only the gap having higher mass flow rate has been considered for simulation. A background study has been done to understand the effect of different clutch parameters on drag losses. Based on the understanding from the literature study, two groove patterns- inclined grooves and waffle grooves have been designed and analyzed in this thesis work. A simplified model with periodic boundary condition and a complete single disc model have been set up and simulated to compare the two groove patterns. To reduce the computational time, at first, a periodic model is set up for groove study. Due to numerical instability observed in the results obtained by using model with periodic boundary condition, the complete single disc model is used for further groove study and comparison. To understand the effect of rotation on grooves, two models have been set up, one with stationary grooves and the other with rotating grooves. While performing the simulations, the temperature and the oil properties have been considered constant. As there were no test results available, the CFD results could not be validated. Convective heat transfer coefficient is estimated to compare the cooling effect of different grooves. An optimal groove pattern would be the one that dissipates oil faster and efficiently out of the clutch pack, and at the same time has better cooling effect. From the results obtained, the inclined grooves were more efficient than waffle grooves in dissipating oil and reducing drag losses. On the other hand, waffle grooves have higher convective heat transfer coefficient when compared to inclined grooves and are better for cooling.