Models for Flow Rate Simulation in Gear Pumps: A Review

Gear pumps represent the majority of the fixed displacement machines used for flow generation in fluid power systems. In this context, the paper presents a review of the different methodologies used in the last years for the simulation of the flow rates generated by gerotor, external gear and crescent pumps. As far as the lumped parameter models are concerned, different ways of selecting the control volumes into which the pump is split are analyzed and the main governing equations are presented. The principles and the applications of distributed models from 1D to 3D are reported. A specific section is dedicated to the methods for the evaluation of the necessary geometric quantities: analytic, numerical and Computer-Aided Design (CAD)-based. The more recent studies taking into account the influence on leakages of the interactions between the fluid and the mechanical parts are explained. Finally the models for the simulation of the fluid aeration are described. The review brings to evidence the increasing effort for improving the simulation models used for the design and the optimization of the gear machines

Lumped Parameters Model of a Crescent Pump

This paper presents the lumped parameters model of an internal gear crescent pump with relief valve, able to estimate the steady-state flow-pressure characteristic and the pressure ripple. The approach is based on the identification of three variable control volumes regardless of the number of gear teeth. The model has been implemented in the commercial environment LMS Amesim with the development of customized components. Specific attention has been paid to the leakage passageways, some of them affected by the deformation of the cover plate under the action of the delivery pressure. The paper reports the finite element method analysis of the cover for the evaluation of the deflection and the validation through a contactless displacement transducer. Another aspect described in this study is represented by the computational fluid dynamics analysis of the relief valve, whose results have been used for tuning the lumped parameters model. Finally, the validation of the entire model of the pump is presented in terms of steady-state flow rate and of pressure oscillations

Lumped parameter model and experimental tests on a pressure limiter for variable displacement pumps

The paper presents the lumped parameter model of a pressure limiter for axial piston pumps developed in the Simcenter Amesim® environment. The control includes both the absolute and differential (load sensing) pressure limiter in a single body. The continuous position valve was tested experimentally alone on a test rig in order to estimate the discharge coefficients required for tuning the model. The tests were performed at imposed positions of the spool and the corresponding modulated pressure and control flow through the valve were measured. A contactless transducer was used for measuring with a very high accuracy the spool position. The influence of the bleed orifice on the pressure gain was also measured experimentally. It was found that the discharge coefficients have a significant influence on the hydraulic characteristic of the valve with also a consequence on the dynamic behavior of the entire displacement control

Analysis of the flow rate through rotating shafts in lubricating circuits

The paper presents the CFD simulation of the oil flow distribution in a rotating system. The aim of the study is to validate the modelling approach for applications in dimensioning and analysing lubrication circuits. A specific experimental assembly was manufactured for measuring the flow rate distribution in a rotating shaft enclosed in a liner with axial inlet and three radial outlets. The flow rate of each outlet was measured by a dedicated turbine flow meter. It was found that, except for high fluid viscosities, the flow rate through the farthest outlet is the highest, due to the inertia of the oil that tends to flow straight on until the last outlet, despite the longest distance, instead of leaving the axial channel through the first radial holes. The angular speed has a slight effect in increasing the nonuniform flow distribution and a significant influence in decreasing the feed pressure. It has been demonstrated that the simulated results are reliable, and the methodology can be used for designing properly the circuit layout in order to obtain a homogeneous flow distribution

Comparison of 0D and 3D Hydraulic Models for Axial Piston Pumps

Abstract In this the paper, a comparison between a 0D and a 3D model for the simulation of an axial piston pump is presented. The lumped parameter approach implements a detailed mathematical model developed in the Amesim® environment for the evaluation of the geometric features of the variable chambers. The commercial tool PumpLinx® has been used for the 3D computational fluid dynamics model. The aim is to assess the capability of the 0D model in predicting the main quantities and to evaluate the use of the three-dimensional analysis for fine tuning purposes. The comparison has been performed in conditions of fixed displacement and constant speed. A good agreement was found in the evaluation of the flow ripple and of the chamber pressure history

Comparison of Analytical and Numerical Methods for the Evaluation of the Flow Forces in Conical Poppet Valves with Direct and Reverse Flow

Different methods for the evaluation of the flow forces in conical poppet valves are analyzed. The equation derived from the conservation of the fluid momentum is contrasted with a formulation obtained from the Bernoulli's equation and with computational fluid dynamics (CFD) simulations performed through two commercial codes, PumpLinx and Flow Simulation. Three different poppet angles and two flow directions are analyzed. In some operating conditions, a significant difference was found between the analytical formulation and the outcomes of the CFD simulations in case of reverse flow

The Working Hydraulics of Valve-Controlled Mobile Machines: Classification and Review

Productivity, reliability, controllability, flexibility and affordable costs represent key aspects in mobile machines. Additionally, due to the high fuel price and to the introduction of stringent emission regulations for diesel engines, the reduction of fuel consumption while persevering the existing performance is the current demand. In order to satisfy and maximize the above requirements, different hydraulic system architectures have been developed during the last decades. Both academia and industry have been investing considerable resources delivering numerous outcomes that require a classification. This review paper closes this gap by analyzing and classifying the working hydraulics of non-hybrid, valve-controlled mobile machines starting from the 1980s to the state-of-the-art. Hydraulic layouts are addressed and categorized by both discussing their fundamentals and evolutions, and by pointing out their pros and cons in a way to provide the readers with a comprehensive overview of the systems currently available on the market and at the research stage

Modelling and Validation of Cavitating Orifice Flow in Hydraulic Systems

Cavitation can occur at the inlet of hydraulic pumps or in hydraulic valves; this phenomenon should be always avoided because it can generate abnormal wear and noise in fluid power components. Numerical modeling of the cavitation is widely used in research, and it allows the regions where it occurs more to be predicted. For this reason, two different approaches to the study of gas and vapor cavitation were presented in this paper. In particular, a model was developed using the computational fluid dynamics (CFD) method with particular attention to the dynamic modeling of both gaseous and vapor cavitation. A further lumped parameter model was made, where the fluid density varies as the pressure decreases due to the release of air and the formation of vapor. Furthermore, the lumped parameter model highlights the need to also know the speed of sound in the vena contracta, since it is essential for the correct calculation of the mass flow during vaporization. A test bench for the study of cavitation with an orifice was set up; cavitation was induced by increasing the speed of the fluid on the restricted section thanks to a pump located downstream of the orifice. The experimental data were compared with those predicted by CFD and lumped parameter models

Evaluation of Tooth Space Pressure and Incomplete Filling in External Gear Pumps by Means of Three-Dimensional CFD Simulations

The paper presents the computational fluid dynamics simulation of an external gear pump for fluid power applications. The aim of the study is to test the capability of the model to evaluate the pressure in a tooth space for the entire shaft revolution and the minimum inlet pressure for the complete filling. The model takes into account the internal fluid leakages and two different configurations of the thrust plates have been considered. The simulations in different operating conditions have been validated with proper high dynamics transducers measuring the internal pressure in a tooth space for the entire shaft revolution. Steady-state simulations have been also performed in order to detect the fall of the flow rate due to the incomplete filling of the tooth spaces when the inlet pressure is reduced. It has been demonstrated that, despite the need of a compromise for overcoming the limitation of considering fixed positions of the gears’ axes and of the thrust plates, significant results can be obtained, making the CFD approach very suitable for such analyses

Passi nell'oleodinamica. Vol. 1-2

“Passi nell’Oleodinamica” testimonia un cammino di conoscenza molto esteso nel tempo che è iniziato nei primi anni ‘80 al Politecnico di Torino. Questa esperienza, che non ha mai subito pause e che tuttora è ricca di nuovi stimoli, è nata e si è formata nell’intento di riuscire a trasmettere ai tantissimi allievi ingegneri l’entusiasmo e la curiosità per una disciplina allora relativamente sconosciuta che ancora oggi non riceve quella attenzione che, per certo, meriterebbe. Questo volume ha anche le sue peculiarità che il lettore attento potrà progressivamente porre in luce. Il contenuto è assai vasto ed in qualche modo testimonia un approccio metodologico originale. Ciò è frutto sia degli aspetti didattici sia delle molte e fruttuose collaborazioni di ricerca che, nel tempo, si sono sviluppate. Sussiste l’auspicio che possa risultare di aiuto a quanti per studio o per professione avranno la passione e la volontà di servirsene. A coloro che lo faranno va il pensiero riconoscente e le scuse per le indubbie manchevolezze ed omissioni unitamente all’augurio sincero di un proficuo lavoro