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CFD analysis of the hydraulic losses of a gearbox: model validation and results

Franco Concli, Carlo Gorla
Politecnico di Milano

Efficiency improvement is the new challenge in all fields of design. In this scenario the reduction of power losses is becoming more and more a main concern also in the design of power transmissions. and appropriate models to predict power losses are fundamental in order to reduce them, starting from the earliest stages of the design phase. Gear power losses are strongly related to lubrication, with those load dependent coming from the frictional effects in the lubricant film and those load independent mainly deriving from squeezing, churning and windage effects. Some models, obtained on the basis of experimental tests, can be found in literature which describe the influence of gear geometric and kinematic parameters on hydraulic losses. Nevertheless the authors maintain that a deeper understanding of the physical phenomena responsible for gear losses is still needed in order to improve existing models and CFD simulation can be an effective approach for such investigation.
Marchesse et al., on the basis of a state of the art on the application of CFD to gear power losses, applied CFD models to study windage losses of gears and have validated their results by means of experimental tests. Hill et al. studied trough CFD simulations the influence of different shrouding configurations on the windage power losses. Concli et al. applied CFD models to study oil squeezing power losses of gears and churning power losses of planetary speed reducers and have validated their results by means of experimental tests. In order to improve the understanding of the mechanisms involved in hydraulic losses, CFD simulations have been performed in order to investigate the effect of the same parameters studied experimentally by FZG, and the numerical results have been compared with the available experimental results. In the first phase of the activities, single discs and gears have been considered. The quite good accordance between CFD simulation and experimental tests has confirmed that CFD represents an effective approach to study windage power losses. In this paper, the effect of the tip diameter, the face width and the rotational speed on the hydraulic losses (windage + squeezing) on two meshing gears have been investigated by means of CFD simulations and validated with experimental data. The results appear in good agreement.