A methodology for investigating the influence of hydrodynamic effects in gerotor type positive displacement machines

Positive displacement gerotor machines consisting of co-rotational and internally-meshed inner and outer rotors are widely used in liquid pumping applications. The necessary clearance gap between rotor profiles influences the contact behaviour and the internal leakage occurring between working chambers at different pressures. These depend on the dynamics of the idler rotor, which has not previously been investigated. This paper introduces a new approach to modelling the rotor dynamics, including the influence of hydrodynamic effects at the rotor contacts, bearing losses and the pumping torque. Epitrochoidal rotor profiles are used to investigate the influence of rotor geometry, clearances, and misalignment. The model provides insight into the effect of operating conditions, fluid properties, and material selection on the minimum film thickness achieved between the rotors, and the variation in clearance gap height. These results are essential for understanding how gerotor machines can be optimised to achieve high efficiency and a long operating life.