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• A numerical model for the analysis of the compensation mechanism of an aerospace fuel delivery pump is presented. • Coupled fluid and structural effects in lubricating gaps are considered in the analysis. • Effect of frictional forces is shown to create a hysteresis effect on the bearing motion. • Experimental measurements are performed to validate the findings of the numerical model. External gear pumps (EGPs) are one of the most common choices in aerospace engines as a fuel delivery pump. These units usually include a pressure compensation system that defines the lubricating gap at the lateral side of the gears. This lubricating interface is a critical design aspect, which strongly affects the reliability as well as the mechanical and volumetric efficiencies of the pump. Major challenges in designing these lubricating gaps in aero engine fuel pumps, include high operating speeds, delivery pressures and low viscosity of the working fluids. Virtual prototyping methods present a fast and efficient design tool and have the potential to improve the EGP's reliability and efficiency. This paper presents a study on the pressure compensation system of a fuel delivery EGP and shows how the presence of frictional forces opposing the motion of the compensating element significantly affect the lubricating performance of the unit. The presence of these frictional forces produces an effect of hysteresis on the axial balance system, so that the lubricating gaps that develop within the pump at a certain operating condition depend on the previous operating state. This effect was captured in an experimental setup purposely developed for this study at Rolls-Royce. Within this work, this behavior was also reproduced numerically, through a coupled fluid structure interaction – elastohydrodynamic (EHD) model that includes the modeling of these frictional forces. After detailing the implementation of the lateral gap model, this paper presents measurements from carefully conducted experiments which correlate with the simulated predictions of the influence of frictional forces on the performance of a reference EGP design under study. [ABSTRACT FROM AUTHOR]

External gear pumps are one of the most commonly used types of positive displacement machines in high pressure hydraulic control systems, fuel-injection and fuel transport systems. Despite many merits of the traditional external gear pump design with involute teeth, the significant flow non-uniformity intrinsic of such design is considered to be a detrimental aspect, since it causes undesired noise emissions and mechanical vibrations. A disruptive concept of continuous-contact helical gear pumps (CCHGP) was proposed and successfully commercialized in the recent past. Such concept was proven to have clear advantages in terms of noise emissions. However, a clear interpretation of the displacing action and the transient features of the delivery flow was never addressed in past literature. This paper addresses this gap by first discussing the family of gear profiles suitable for implementing the CCHGP design. Subsequently, an analysis on the kinematic flow ripple is given, showing how such design concept can reduce or even eliminate the kinematic flow pulsations. The paper also presents a numerical approach for modelling the operation of CCHGPs, starting from the modeling of the geometric features necessary for a fluid dynamic analysis based on a lumped parameter approach. For model validation purposes, a commercial CCHGP was tested at the authors’ research center, and the simulation results were compared against the experiments, to show the level of accuracy of the model, as well as it potentials for future design studies. [ABSTRACT FROM AUTHOR]

External Gear Pumps are used in various industries to pump non-Newtonian viscoelastic fluids like plastics, paints, inks, etc. For both design and analysis purposes, it is often a matter of interest to understand the features of the displacing action realized by meshing of the gears and the description of the behavior of the leakages for this kind of pumps. However, very limited work can be found in literature about methodologies suitable to model such phenomena. This article describes the technique of modelling external gear pumps that operate with non-Newtonian fluids. In particular, it explains how the displacing action of the unit can be modelled using a lumped parameter approach which involves dividing fluid domain into several control volumes and internal flow connections. This work is built upon the HYGESim simulation tool, conceived by the authors’ research team in the last decade, which is for the first time extended for the simulation of non-Newtonian fluids. The article also describes several comparisons between simulation results and experimental data obtained from numerous experiments performed for validation of the presented methodology. Finally, operation of external gear pump with fluids having different viscosity characteristics is discussed. [ABSTRACT FROM AUTHOR]

• A fully coupled multi-domain multi-physics dynamic system is presented. • Three components of the loadings are explained and analyzed in detail. • The patterns of 3D transient loadings and dynamics are discussed with simulation results. • A design routine for the axial balancing mechanism of helical gear pumps is provided. • The pattern of wear seen from experiments can be replicated by the wear model. This paper presents a multi-domain dynamic simulation model for continuous-contact helical gear pumps, which is an unconventional hydraulic pump design that is capable of canceling its kinematic flowrate variation. In this model, the fluid dynamics (in its lumped-element representation) are fully coupled in a closed feedback loop with other physical domains, including critical tribological interfaces, 3D dynamic loadings on the solid parts, dynamics, and micro-vibrations of the rotors. The model is compared to the analytical derivation and experimental measurements to prove its validity. The model can be used to provide predictive simulations for existing designs, or as a tool to optimize the design to provide better hydrostatic balancing for future iterations of hydraulic pump designs. [ABSTRACT FROM AUTHOR]

In this paper we present a preconditioned multi-domain algorithm applied to the elliptic kernels arising from the spectral collocation of the incompressible Navier–Stokes equations in three space dimensions with one homogeneous direction. The technique, based on the iterative solution of the Schur complement matrix, allows for efficient numerical solution of the operators in complex geometries consisting of a collection of non-overlapping rectangular subdomains. The method is shown to be nearly optimal in terms of condition number behavior in a double path of refinement strategy, i.e. whenever both the number of Legendre modes and the number of subdomains are significantly increased. It is thus well suited for engineering applications in the fields of direct numerical simulation and large eddy simulation of turbulence. [Copyright &y& Elsevier]

• A novel model for curve-constricted leakage flows in hydraulic gear pumps is presented. • The flow model is applicable over a wide range of flow regimes including localized cavitation. • The model is developed in dimensionless form based on sets of CFD simulations. • Model validation is achieved through experiments conducted on a custom test apparatus. The internal leakage flows in external gear and gerotor pumps are often represented by flow through curved constrictions. The nature of this flow can vary from laminar to turbulent and the flow can experience localized cavitation too. In the current literature, there is a scarcity of techniques for accurately modelling such curve-constricted flows which limits the accuracy of the current simulation tools for gear pumps. This paper presents a novel flow model for curve-constricted geometries that is applicable over a wide range of flow regimes including localized cavitation. Using a dimensionless form, the proposed model characterizes the constriction flow velocity as the function of the constriction shape, the pressure difference, and a properly defined cavitation indicator. The functional relationships between these dimensionless parameters are developed based on CFD simulations. The flow model is validated by the means of several experiments conducted on a custom test apparatus. The model presented in this paper can be incorporated in the lumped parameter simulation tools widely used for modelling gear pumps, improving their accuracy in predicting the internal leakages. Consequently, this model will also aid the development of novel energy efficient gear pump designs, where such leakages are kept to a minimum. [ABSTRACT FROM AUTHOR]

• The proposed simulation model evaluates torque efficiency of hydraulic orbit motors. • The model considers deformation effects and frictional losses of the hydraulic motor. • Both the torque pulsation and the mechanical efficiency are experimentally validated. • The simulated torque agrees with the measurements. • The micro-motion of rotor, subjective to forces, is evaluated numerically. This article presents a method for evaluating the torque output of orbit type displacement machines. Orbit machines are commonly used as hydraulic motors, for applications involving low speed and high torque output. The evaluation of the actual shaft torque as well as the hydro-mechanical efficiency in positive displacement machines is a topic that still presents challenges related to the evaluation of the torque losses associated with the functioning of the unit. This paper proposes a method of evaluating the torque efficiency starting from the evaluation of the instantaneous pressurization of each displacement chamber through a lumped parameter approach. From the instantaneous pressure in each chamber of the orbit motor, the contact forces normal to the rotor profiles are evaluated using a contact mechanics formulation accounting for the energy dissipation. The proposed algorithm computes the friction losses at the contact points to evaluate the net torque output of the orbit motor. Besides accounting for the frictional losses, the main elements of novelty of this approach also include the evaluation of the component deformation, instead of making rigid body assumptions. Experiments are performed on a set of reference orbit motor units to evaluate the torque output at different operating conditions. A good agreement between the simulated output torque and the one measured from experiments was observed, in terms of both instantaneous and mean values. The corresponding comparison of mechanical efficiency map is also presented. This shows the potential of the proposed method, which can potentially be extended to other types of gear machines, to evaluate the net shaft torque. [ABSTRACT FROM AUTHOR]

This paper explores the significant impact of thermal effects on the performance of Swashplate-Type Axial Piston Machines, a crucial aspect often overlooked in current numerical analyses primarily focused on energy efficiency prediction and machine design optimization. Existing methods commonly neglect or only partially account for thermal dynamics and heat transfer within both fluid and solid domains, resulting in inaccurate power loss predictions and hindering designers' ability to enhance energy efficiency and durability. To address this gap, we present a comprehensive thermal model that fully couples the thermal behavior of the entire machine. This model incorporates mass and energy conservation in displacement chambers and slipper pockets, dynamics of floating bodies, Reynolds equation, and energy conservation in lubricating interfaces. Furthermore, it considers heat transfer in floating bodies and thermo-elasto-hydrodynamic effects induced by pressure and thermal deformation. Validation against experimental data demonstrates the accuracy of the model in predicting solid body temperature distribution and overall machine efficiency. By comparing machine efficiencies with an isothermal model, we highlight the critical importance of considering thermal effects. Additionally, our model offers insights into key power loss sources across various operating conditions, contributing to a deeper understanding of machine performance and aiding in future design optimizations. [ABSTRACT FROM AUTHOR]

Understanding how environmental pollutants influence plant occurrence, growth, and development is key for effective management plans and potential bioremediation. Rare plants, such as orchids, may occur in modified habitats and on soils containing heavy metals, yet their ecological and physiological responses to heavy metals is poorly understood. We investigated the influence of heavy metal pollution on orchid growth rates and interactions with soil fungal mutualists by comparing a large population of the orchid Epipactis helleborine (L.) Crantz subsp. tremolsii (Pau) E. Klein that grows on mine tailings in south-west Sardinia (Italy) with a population that grows on non-contaminated soils in central Sardinia. Soils of the contaminated site had high levels of heavy metals and low organic matter and nutritive elements content. We performed a morphological analysis on twenty individuals that have been subjected to measurement of bioaccumulation and translocation of heavy metals. Fungi associated with the roots of plants from the contaminated and uncontaminated site were grown and identified by DNA barcoding approach. Plants from the contaminated site were smaller than the ones growing in the uncontaminated site and were found to be able to tolerate heavy metals from the soil and to accumulate and translocate them into their organs. Fungi belonging to the genus Ilyonectria (Ascomycota) were found both in contaminated and uncontaminated sites, while an unidentified fungus was isolated from roots in the contaminated site only. These results are discussed in terms of orchids' tolerance to heavy metals and its physiological and ecological mechanisms. The role of contaminated habitats in harbouring orchids and peculiar taxa is also discussed. • Epipactis helleborine subsp. tremolsii grows on a heavy metal polluted mining area. • Individuals resulted significantly smaller in the contaminated site. • Accumulation and translocation of pollutants in plants' organs were confirmed. • Contribution of radical fungi on metal tolerance seems to be weak. [ABSTRACT FROM AUTHOR]

• The proposed simulation model evaluates different flow, force features of a Gerotor. • The model considers different fluid–structure interactions of the rotors. • Flow rate, pressure pulsation and mechanical efficiency are experimentally validated. • Torque losses are quantified, considering possible asymmetry of the axial gap. Gerotors are compact, inexpensive and robust pumps generally used in hydraulic systems. Owing to their characteristic operation at low pressure (up to 30 bar), these units can be modelled using relatively simple tools considering only their fluid dynamics aspects. However, some commercially available Gerotors operate at higher pressures so that material deformation effects cannot be neglected under such conditions. This paper presents an omni-comprehensive simulation approach for Gerotor units that considers the fluid–structure interaction effects at the lateral lubricating gaps and related to the contacts between the rotors. The numerical tool consists of different submodels which allow the evaluation of the fluid dynamic features of the flow through the pump considering micro-motion effects of the rotors. This paper particularly details the novel aspects of the simulation approach, which is the introduction of submodels that account for fluid–structure interaction effects: the lateral lubricating gap models and the rotor contact models, both based on the solution of the Reynolds equation considering the deformation of the solid parts. For the model validation, a commercially available pump able to operate above 100 bar was tested at the authors' research center. The comparison between the simulation results and the experimental data clearly show the good accuracy of the model, in terms of volumetric flow and port pressure pulsation. In particular, the model allows predicting both the volumetric and the torque efficiency of the unit. Furthermore, the simulation results permit to interpret the reasons for instances of wear present in the unit. [ABSTRACT FROM AUTHOR]