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This paper presents a model formulation for balanced twin lip vane pumps and an experimental activity to validate the model. The simulation model begins with a geometrical module that preprocesses the CAD drawings of a given unit. The model then performs a fluid dynamic analysis using a lumped-parameter formulation to solve for the pressures inside properly defined control volumes within the unit. The fluid dynamic model is solved simultaneously with a motion module that evaluates the planar motions of the vanes using Newton's law of motion and with a lubricating interface solver based on the Reynolds equation. Contact dynamics formulations and elastohydrodynamic relations are applied at the vane locations in contact with the cam ring. The comparison with experimental results highlights a good match in volumetric and hydromechanical efficiencies. The measured outlet pressure ripple matches the simulated one for all tested speeds and pressures. The paper also shows a breakdown of the distribution of volumetric and power losses arising from various components of the machine. The proposed methodology is computationally inexpensive, so it can be used in future design and optimization studies aimed at improving the performance of such units. • A novel simulation approach for high-pressure pressure balanced vane pumps. • Multiphysics approach coupling mixed lubrication, vane motions, and fluid dynamics. • Capturing details in cam ring profile, fluid properties, clearances, vane designs. • Experimental activity performed to validate the modeling approach. • Good accuracy for pressure pulsations, volumetric and hydromechanical performance. [ABSTRACT FROM AUTHOR]

Highlights: [•] A model to evaluate fluid properties considering the dynamic features of cavitation is presented. [•] The new model for the evaluation of fluid properties is suitable for lumped parameters models. [•] The paper studies the operation of gear pumps under cavitating conditions. [•] Experimental activity on a gear pump was performed to validate the modelling approach. [Copyright &y& Elsevier]

Abstract: In this paper an innovative procedure for determining the optimal design of an external spur gear pump for a particular emission reduction application in automobiles has been proposed. The pump forms the main part of a mechatronic system that controls the flow rate of a mixture of urea in water to catalytically reduce emissions in diesel engines. The proposed research proves to be an advance in gear machine design by using a multi-objective based genetic algorithm, to determine the optimal design of the gears and the casing by maximizing the volumetric efficiency, minimizing pressure overshoots, localized cavitation and noise emissions. The research uses HYGESim (HYdraulic GEar machines Simulator) simulation tool, which is being developed by the authors’ research group, for calculating the important performance features of the machine. The best designs for the machine based on enhancement in performance are presented. Results in terms of simulations and tests which validate the effectiveness of the proposed novel design methodology are also presented. [Copyright &y& Elsevier]

Abstract: This paper presents a novel modeling approach for studying the lateral lubricating gap between sliding lateral bushes and spur gears in external gear machines. Pressure compensated lateral bushings are important design elements for efficient operation of an external gear pump or motor, being responsible for functions such as sealing the displacement chambers, guaranteeing a proper timing for the connections with outlet and inlet port limiting pressure peaks and cavitation. As regards the sealing function, they must be designed with the two main goals of reducing power losses due to leakages and of maintaining full film lubrication in the gap, to minimize shear stress and prevent wear in the elements. Because of the complexity of the simultaneous processes that characterize the operation of this kind of units, only limited research has been performed on modeling the lubricating gap in the past. The model presented in this paper is the first tool that can predict the lateral lubricating gap features, accounting for the main features of machine operation. A Computational Fluid Dynamics solver that solves for the flow field in the lubricating gap is coupled with a model of the axial motion of the lateral bushes to determine the lubricating gap heights. The model also interacts closely with a lumped parameter model as well as a geometric model of gear teeth control volumes, and therefore provides a tool for a “complete simulation” of the unit. The forces acting on the lateral bushing are seen to lead to an axially balanced condition. An original method of decomposition of forces was developed to perform an analysis of the effect of the hydrodynamic as well as hydrostatic forces acting on the bushing. It was found that the hydrodynamic generation of pressure from the “wedge” mechanism determines the orientation of the lateral bushing at axial balance. Gap heights and the resulting power losses from the lubricating gap are also calculated for a range of operating conditions. Using the proposed methodology, competing designs of lateral bushes can be evaluated and optimized for low chances of wear, as well as low losses. The tool developed has the potential to be used to drive design of gear machines with greater efficiency and reliability. [Copyright &y& Elsevier]

Abstract: The modelling of positive displacement machines has to deal with the complexity of solving the flow through the unit in presence of simultaneous macro and micro-motions of the moving parts. In this paper, the main phenomena characterizing the operation of the spur external gear units are successfully analyzed by means of a numerical model developed by the authors. The model, here referred as HYdraulic GEar machines Simulator (HYGESim), consists of different modules: a fluid dynamic model, a model for the evaluation of the movements of the gears’ axes of rotation and a geometrical model. When performing a HYGESim simulation, these models are executed in a co-operative simulation. Starting directly from the CAD drawing of the unit as input, the simulation tool permits to describe the main features of the flow though the machine and to evaluate the possible wear of the casing wear accounting for a detailed description of the geometry of the internal components (i.e. teeth’s profile, design of lateral bushes). The paper describes the modelling approach and the main potentials of the simulation tool, pointing out how it can be utilized for design purposes. As a matter of fact, HYGESim permits to analyse the effects of the main design parameters on important aspects like efficiency, internal pressure peaks, local cavitation and fluctuations of flow at unit’s ports (associated with fluid borne noise). The presented tool also allows the evaluation of the radial movements of the gears’ axes of rotation resulting from the forces exerted on both gears, thus permitting to study the balancing feature related to a certain design. The paper also presents several comparisons between simulation results and experimental data coming from an experimental activity specifically performed for validation of the presented tool. [Copyright &y& Elsevier]

Abstract: This paper describes a numerical procedure for the prediction of the homogenizing performance of high pressure homogenizing valves used in diary plants. The method is based on a strict interaction between a complex CFD code and a simple homogenizing simulation code developed by the authors. This latter implements a mathematical model for the evaluation of droplets break-up, that needs an accurate evaluation of few significant fluid dynamic parameters in the whole fluid dynamic domain inside the valve. Due to the relevant pressure gradients within the flow and to the possibility of cavitation, particular attention has been paid in defining the fluid model, the mesh and the parameters required for CFD simulations. Notwithstanding the quite simple model of the homogenizing process, comparatively with the complexity of phenomena involved, the first results obtained are in general agreement with the experimental data available. These results point out the potential of the procedure proposed as a starting point for further implementation of more complex effects. [Copyright &y& Elsevier]

Abstract: This paper presents a numerical model for the simulation of a swash-plate axial piston pump, focusing on the characterization of fluid properties. As it is well known, the reduction of flow oscillations (which generates pressure ripples and produces vibration and noise in the entire circuit) and the avoidance of cavitation are the major problems in the design of these pumps. Developing a simulation code can be very useful for component optimisation in order to predict and reduce the undesired phenomena. The paper first gives a quick overview on a previously developed pump model; afterwards four different models of the fluid are presented: they take into account cavitation in different ways. Their aim at characterizing as well as possible the unsteady and erratic cavitation features in a simplified manner, in order to apply the models to the simulation of hydraulic components. In the second part of the paper an application is shown of these models to an axial piston pump: a few results are presented and compared with available test data. The effects of the fluid models on the predicted pump performance are shown and commented. [Copyright &y& Elsevier]