Experimental and Numerical Assessment of an Axial Piston Pump’s Speed Limit

A high power density is a crucial requirement to axial piston pumps. It is determined by the machines’ maximum pressure and speed. At high rotational speeds, cavitation leads to the partial filling of the cylinders with gas and causes a breakdown of the delivery flowrate. A further increase of the speed limit requires a deep understanding of these effects. Since they are very hard to capture metroligically, power density has not significantly increased over the past 20 years. Recently, the steadily increasing availability of computational power has made possible the simulation, visualisation and analysis of the flow effects inside the pumps by means of computational fluid dynamics. In this paper, a criterion and a method for the precise determination of the pumps’ speed limit are presented. The description of the experimental setup is followed by flow characteristics measured at varying suction and delivery pressures. Afterwards, a CFD model of the pump is presented. It is shown how the measured flow characteristics can be reproduced in the simulation. The flow phenomena causing the speed-limiting cavitation effects are identified by a detailed analysis of the CFD results. Eventually, constructive countermeasures allowing increased rotational speeds and thereby power densities are proposed.