A CFD Approach for the Simulation of an Entire Swash-Plate Axial Piston Pump Under Dynamic Operating Conditions

The paper proposes a CFD approach for the simulation of a swash-plate axial piston pump including the full 3D geometry of the real component. The numerical model is used to predict the fluid-dynamic behavior of the volumetric machine under different operating conditions. The analysis is carried out on a 9-piston pump component to highlight the capabilities of the proposed approach to address any type of swash-plate axial piston pump.

A multi-purpose CFD software is adopted for developing the modeling approach. Different meshing techniques are integrated in order to reproduce all the motions that characterize the axial piston pumps. Overset meshing procedure is used to simulate the slippers’ motion on the swash plate and in the piston-slipper ball-joint regions, similarly the cylinder chambers are simulated by means of an overset method. The alternating motion of the piston is accounted for by sliding interfaces with the neighboring regions. Finally, the housing of the pump including the 9 pistons is modelled by means of the overset mesh technique. The multiple dynamics of the different moving elements are implemented in terms of superposing motions in order to reproduce the real position time histories as a function of the rotational speed and swash plate position.

The prediction capabilities of the fluid-dynamics behavior of the volumetric machine is strictly depending on the modeling of the leakages that characterize the coupling of the many components of the pump. The proposed numerical model includes all the leakages of the real geometry and nominal values are assumed (i.e. 10μm) throughout the entire simulation.

Particular care is devoted to represent the physical properties of the fluid; thus, a pressure-dependent fluid density approach is adopted to account for the real operating fluid bulk modulus to improve the performance prediction of the pump under real operating conditions. Moreover, the turbulent behavior of the flow is addressed by means of the two equation k-omega SST model. The grid size and mesh quality of the moving regions is optimized as the tradeoff between the results’ accuracy and the computational effort. Similarly, the time step adopted in the simulations and the number of simulated pump rotational cycles have been optimized in order to reach a cyclic convergence of the results within a simulation time suitable with the design process of the volumetric machine.

Therefore the proposed modeling approach is able to simulate the entire machine under dynamic operations; the numerical results are discussed in terms of flow ripple, pressure distribution and fluid-dynamics forces acting on the different moving parts.