Flow effects in axial piston pumps
Research objective
Due to their high efficiency and their robustness, axial piston pumps are widely spread in the field of stationary and mobile hydraulics. The delivering flowrate of the displacement machines is limited by the occurrence of cavitation and partial filling of the cylinders with gas at high rotational speeds. The sudden implosion of gas bubbles during the compres-sion phase within the high pressure carryover causes cavitation erosion and mechanical damage to the component walls.
These effects are hard to capture metrologically inside the guickly rotating and highly pressurized machines. The steadily growing availability of computational power makes the simulation, visualization and analysis of the flow effects inside the pumps possible by means of computational fluid dynamics.
Based on that, constructive measures are derived to reduce cavitation and to prevent failure of the pumps‘ components. Thereby, lifetime and reliability of the machines can be increased. The developed detail improvements are afterwards being virtually tested.
Approach
Cavitation erosion on the valve plate
Using moving and displacing grids, a CFD model of the rotating kit has been developed in order to analyse the influence of constructive details on the fluid flow. Jet cavitation, compression and decompression during carry-over have been identified as dominating effects concerning erosion and component damage. Derived countermeasures are an extension of the low pressure kidney and the redirection of the cavitation jets into regions off the walls using precompression bores in the valve plate.
The project "Holistic simulation of unsteady flow in piston pumps to improve the operating behaviour and performance" (Ref.-No. AiF15106 BR/1) was financed and supervised by the Forschungskuratorium Maschinenbau e. V. – FKM, Lyoner Straße 18, 60528 Frankfurt am Main. In the scope of the Programme to promote Industrial Collective Research it was funded by the German Federation of Industrial Research Associations (AiF) with means of the Federal Ministry of Economic Affairs and Energy (BMWi) on the basis of a decision by the German Bundestag.