Investigation of the impact of Oil Aeration on Outlet Flow Oscillations in External Gear Pumps

This paper studies the effect of the air release/ adsorption processes on the instantaneous output flow of external gears pumps for high pressure fluid power applications. Being used mainly in open circuit applications, external gear pumps are subjected to cavitation due to air release. However, existing approaches to study oil aeration are not suitable to describe the effects on the displacing action of positive displacement machines. Examples are given by the too simplified approaches for lumped parameters modelling based on Henry’s steady-state law or the CFD based approaches which requires unrealistic assumptions on the operating features of the machine. The present study overcomes these limitations by introducing a novel model for studying the dynamic air release/adsorption processes suitable for lumped parameter models. Previously validated by the authors for the cases of simple compression/expansion processes, the model was integrated in an existing simulation tool (HYGESim) specifically developed for the simulation of external gear pumps and motors. This work particularly focuses on the potentials of the new simulation approach for studying the effects of the air release on outlet flow pulsations. For the reference case of an external gear pump, an experimental set-up was used to validate the numerical predictions. The results presented in this research show how dynamic aeration features affect the mechanisms of delivery flow pulsations. Being directly affected to fluid borne noise, the present study can drive future research about how to reduce pressure fluctuations by controlling air entertainment properties.