Cfd-based design and experimental assessment of a gerotor pump for aircraft applications

Abstract

A pump is a device that transfers fluid from a low-pressure region to a higher-pressure region by converting mechanical energy into hydraulic energy. Its main functions are to transport fluids, increase pressure, and ensure circulation. Pumps are typically used in liquid systems and are driven by power sources such as electric motors, hydraulic systems, or internal combustion engines. The gerotor pump, classified under gear pumps, is a positive displacement type consisting of two intermeshing gears. The inner gear has fewer teeth than the outer gear, and their eccentric rotation generates the volumetric variations required for suction, compression, and discharge. Fluid enters the cavities of the gerotor through the suction port, becomes pressurized due to the chamber volume change during eccentric rotation, and is subsequently delivered to the system via the discharge port. Gerotor pumps are widely employed in aerospace (power transmission, propulsion system lubrication, and cooling) and automotive industries (fuel and lubrication systems). The design of a gerotor pump must be tailored to the specific requirements of the target system. Key parameters such as flow rate, pressure, temperature, and operating speed are initially defined. Based on these requirements, two-dimensional profiles are developed, ensuring cavitation and filling ratio criteria are satisfied under operational conditions. The inlet and outlet port geometries are then defined in direct correlation with the gerotor profiles. Following this stage, three-dimensional CAD models are generated, and manufacturing is carried out. Experimental testing of the manufactured pump is essential to assess performance and compliance with design requirements. Design deficiencies at this stage may result in financial loss and time delays. Performing Computational Fluid Dynamics (CFD) analyses prior to manufacturing enables prediction of hydraulic performance under operating conditions. CFD provides insight into pump efficiency at specified operating speeds, pressures, and temperatures, thereby minimizing risks of cost and schedule overruns. In CFD studies, three primary leakage mechanisms must be investigated: tip leakage, axial leakage, ,radial leakage and bushing leakage. Each leakage type should be analysed independently for all operating conditions. To validate the numerical models, experimental testing under identical conditions is required. Within the scope of this study, a comprehensive analysis matrix was established to evaluate the hydraulic performance of the gerotor pump under various operating conditions. Both CFD analyses and experimental tests were carried out by systematically varying rotational speed, outlet pressure, and fluid temperature. This approach enabled a detailed investigation of the combined effects of operating parameters on pump performance and internal leakage characteristics. xxiv The results indicate that fluid temperature and outlet pressure are among the most influential parameters affecting pump performance. An increase in operating temperature led to a reduction in fluid viscosity, which significantly increased internal leakage rates and resulted in a noticeable decrease in volumetric efficiency. Similarly, an increase in outlet pressure intensified reverse flow from the high-pressure region to the low-pressure region, further reducing the delivered flow rate. Among the investigated leakage mechanisms, tip leakage was identified as the dominant and most pressure-sensitive leakage type, while axial, radial, and bushing leakages exhibited secondary but non-negligible contributions depending on operating conditions. The numerical results obtained from the CFD analyses showed good agreement with the experimental measurements across the defined analysis matrix. The deviations between numerical and experimental flow rate results remained within acceptable limits, confirming the validity of the developed CFD model. Overall, the findings demonstrate that the proposed CFD-based methodology provides a reliable and efficient tool for predicting gerotor pump performance, supporting design optimization and reducing the need for extensive experimental testing in aerospace pump applications.