This paper examines how the span angle design of its tooth profile affects the motion and pumping performance of a gerotor pump whose outer rotor profile is formed by an epicycloid and hypocycloid and whose inner rotor profile is obtainable by the theory of gearing. When the outer rotors have the same volume, the sealing performance of the rotor profile can be assessed using the curvature difference method, which indicates that sealing remains the same across various span angle designs. The tooth profile is built using mathematical models of the rotor, and fluid and dynamics analyses are conducted to predict actual pump operation. The overall fluid analysis, which models both compressibility and cavitation, clearly illustrates the complexity of the fluid flow inside the pump. Comparisons of the results for three separate span angle designs then reveal that the larger the span angle, the higher the area efficiency, outlet pressure, outlet flow rate, outlet flow velocity, and gas volume. A subsequent dynamics analysis further suggests that different span angle designs may lead to diverse contact force distribution on the inner and outer rotors. Hence, the research results provide useful guidelines for rotor design.

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