Flow Ripple Research Articles

Modeling and optimization of the delivery fluctuation of gear pumps

Presented work aims to minimize the delivery fluctuation of a gear pump through geometrical optimisation of the tooth flank. Therefore, instead of examining various configurations, which would reduce the flow ripple ad hoc, the current study suggests the dependence the delivery fluctuation to the tooth flank profile. Taking into account the secondary derivative of the tooth profile, the optimisation process is able to also affect the secondary delivery fluctuation, which is connected to the compression of the fluid over the meshing cycle. Bezier-Bernstein polynomial curves were used to model the tooth flank in order to satisfy the objective function. A dependency between the total length of the path of contact curve and the flow ripple was found. It is stated in this work that for every design point on a closed path of gear set, there is a threshold on the contact length, over which the resulted flow ripple starts to deviate from the optimum value. That conclusion was used to further enhance the optimisation algorithm. The presented optimum gear profile design was evaluated through a comparative study between every design point and the corresponding solution of the existing state of the art in terms of delivery fluctuation.

Numerical investigation of external radiation noise induced by dipole and quadrupole sources in an axial piston pump

Extensive research has been performed on the reduction of flow ripple and pressure fluctuation in axial piston pumps. However, the acoustic characteristics and sound sources of the external radiation noise induced by the fluid within an axial piston pump body have been rarely studied. In this study, a hybrid method combining computational fluid dynamics (CFD) with computational acoustics (CA) based on the Lighthill's acoustic analogy (LAA) theory was adopted to calculate the external radiation noise. First, a three-dimensional unsteady flow field was calculated by using CFD model, and the consistency between the computed results and experimental test data was verified. Then, the quadrupole and dipole sound sources were obtained based on the LAA theory. After that, the finite element method (FEM) was adopted to numerically analyze the natural modes of the axial piston pump shell, and it had been verified by the experimental modal test. Finally, the external radiation noise induced by the different fluid sound sources was calculated based on FEM/AML (automatically matched layer) vibro-acoustic coupling method. The results show that the quadrupole sound source is the main contributor of external radiation noise. Subsequently, the effects of different triangular groove structural parameters on external radiation noise were studied. This research can provide guidance for engineers in the design of low noise axial piston pumps.

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

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.

Multi-objective optimization of circular-toothed gerotors for kinematics and wear by genetic algorithm

A multi-objective optimization of circular-toothed gerotor gear geometry by genetic algorithm is presented that minimizes the size, flow ripple, adhesive wear, and subsurface fatigue wear (pitting) of the pump, insofar as the geometry is concerned, subject to the constraints to guarantee a feasible profile. Three pump geometries available to the authors used in automotive applications were compared to the optimization results. A clear Pareto front was established that gives insight into the design space of circular-toothed gerotors. The optimization identified that the industry reference pumps were very near to or on the Pareto front, so this work demonstrates mathematically that some circular-toothed gerotors in industry have reached an optimal solution. Another pump geometry is also identified that could be a better compromise between the objective functions than the reference pumps. The methodology presented here can be readily extended to other profile types and the results can serve as a benchmark for comparison.

Analysis of continuous-contact helical gear pumps through numerical modeling and experimental validation

Abstract 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.

Experimental and theoretical studies on the pressure fluctuation of an internal gear pump with a high pressure

In this paper, the flow ripple equation is derived to analyze the effect of working condition on pressure pulsations of an internal gear pump. Results indicate that working pressure has a significant effect on pressure fluctuation of the internal gear pump, while the rotating speed has a complex influence on the pressure pulsation behavior. Then, pressure pulsations of the internal gear pump under different working conditions are discussed by experimental investigations. Results show that the internal gear pump taken for analysis has a low-pressure pulsation at a high working pressure and a relatively high rotational speed. Regarding the frequency spectrum of the pressure pulsation, the dominant frequency is Z* fn, i.e. the product of the tooth number of the driving gear (gear shaft) and its rotational frequency for many working conditions, caused by the inevitable unsteady discharge process of gear pumps. It transforms to the rotational frequency of the gear shaft ( fn) for a high rotational speed or a high operating pressure, but to the rotating frequency of the internal gear ring (2/3 fn) only for a high operating pressure. The occurrence of the two frequencies (2/3 fn and fn) may result from the deformation of the gear ring and the gear shaft under the unbalanced radial forces caused by a high working pressure. Moreover, the frequency spectrum of the inlet pressure pulsation presents some differences from that of the outlet pressure pulsation. This is because the inlet pressure may be influenced by cavity generated at the suction side of the pump.

Theoretical Analysis for the Flow Ripple of a Tandem Crescent Pump with Index Angles

This paper presents a theoretical approach for lowering the outlet flow ripple of a crescent pump by applying a tandem crescent pump consisting of two gear pairs with an index angle between them. The outlet flow of the tandem pump is obtained by summing the flow produced by the two gear pairs, and the flow ripple of the tandem pump can be attenuated by properly selecting the design parameters in terms of the index angle and the displacement ratio between the two gear pairs. A lumped parameter model is presented for evaluating the crescent pump’s flow ripples, and experiments were performed on a single crescent pump to validate the model from the aspects of the steady-state flow-pressure characteristics and the outlet pressure ripples. In this way, the main causes of the flow ripple could be identified by comparing the kinematic flow with the actual flow evaluated by the model. Additionally, simulation results suggested that a tandem pump with an index angle of 13.85° and displacement ratio of 0.5 could lead to a more than 45% decrease in the outlet flow ripple than a single pump with the same displacement in a wide range of operating conditions.

Flow ripple analysis and structural parametric design of a piston pump

The ripple in the outlet flow from a high-pressure piston pump is caused by pressure pulses in the piston cavity when it rotates through the transition region of the valve plate. We propose a parametric design that optimizes the transition region structure of a piston pump valve plate to reduce the ripple in the outlet flow. For a high- pressure piston pump, a theoretical model of the piston cavity is developed that includes fluid compression properties and leakages. The piston pump parametric model is built using AMESIM software and a simulation is conducted. The results show that the ripple in the outlet flow is affected by the outlet pressure and the pump’s speed and by the structure of the pre-compression region of the valve plate. To minimize the ripple in the outlet flow from the piston pump, the structural parameters in the pre-compression region are optimized as the design variables using the software, ISIGHT, which integrates the piston pump parametric model in AMESIM. After optimization, the ripple in the outlet flow rate is, respectively, reduced by 37.05 %, 38.54 % and 41.04 % for outlet pressures of 200 bar, 300 bar and 400 bar. Finally, a flow ripple test experiment is performed to verify the simulation results.

Transient Flow Study of a Novel Three-Cylinder Double-Acting Reciprocating Multiphase Pump

In petroleum industry, the stability of multiphase pumping is highly disturbed by the gas' presence with high content and variable working conditions. This paper is focused on studying the whole working cycle of the novel three-cylinder double-acting reciprocating multiphase pump. Based on the theoretical analysis, the method of computational fluid dynamics (CFD) is adopted to simulate the oil–gas flow in reciprocating multiphase pump. The numerical methodology, involving multiphase model, dynamic grid technique and user defined functions (UDF), is used to deal with in the calculation. The transient flow characteristics in pump cavity are obtained, and the flow ripples of reciprocating multiphase pump are analyzed. Furthermore, the effects of different operating parameters, such as suction and discharge pressures, inlet gas volume fraction (GVFi) on the capacity, and stability of pump, are studied. The results could help to develop and optimize the high-efficiency multiphase pump system.

Simulation Analysis and Experiment of Variable-Displacement Asymmetric Axial Piston Pump

The variable displacement pump control system has greater energy-saving advantages and application prospects than the valve control system. However, the variable displacement pump control of differential cylinder is not concurrent with the existing technologies. The asymmetric pump-controlled cylinder is, therefore, used to balance the unequal volume flow through a single rod cylinder in closed-circuit system. This is considered to be an effective method. Nevertheless, the asymmetric axial piston pump (AAPP) is a constant displacement pump. In this study, variable-displacement asymmetric axial piston pump (VAPP) is investigated according to the same principle used in investigating AAPP. This study, therefore, aims at investigating the characteristics of VAPP. The variable-displacement output of VAPP is implemented by controlling the swash plate angle with angle feedback control circuit, which is composed of a servo proportional valve and an angular displacement sensor. The angular displacement sensor is connected to the swash plate. The simulation model of VAPP, which is set up through the ITI-SimulationX simulation platform, is used to predict VAPP’s characteristics. The purpose of implementing the experiment is to verify the theoretical results. Both the simulation and the experiment results demonstrated that the swash plate angle is controlled by a variable mechanism; when the swash plate angle increases, the flow of Port B and Port T increases while the response speed of Port B and Port T also accelerates. When the swash plate angle is constant, the flow of Port B and Port T increases along with the increase of pump speed, although the pressure-response speed of Port B is faster than that of Port T. Consequently, the flow pulsation of Port B and Port T tends to decrease gradually along with the increase of pump speed. When the pressure loaded on Port B equals to that of Port T, the flow ripple cycle of Port B is longer than that of Port T, whereas the peak flow of Port B is higher than that of Port T. Since the flow ripple of Port T is bigger than that of Port B, Port T should be connected to the low pressure sides or the oil tank so that it does not affect VAPP’s performance. Further, to avoid the backflow of VAPP from Port T to Port B, Port T cannot be loaded alone, and the loading pressure of Port T also cannot exceed that of Port B.

A Hybrid Lumped Parameters/Finite Element/Boundary Element Model to Predict the Vibroacoustic Characteristics of an Axial Piston Pump

Low noise axial piston pumps become the rapid increasing demand in modern hydraulic fluid power systems. This paper proposes a systematic approach to simulate the vibroacoustic characteristics of an axial piston pump using a hybrid lumped parameters/finite element/boundary element (LP/FE/BE) model, and large amount of experimental work was performed to validate the model. The LP model was developed to calculate the excitation forces and was validated by a comparison of outlet flow ripples. The FE model was developed to calculate the vibration of the pump, in which the modeling of main friction pairs using different spring elements was presented in detail, and the FE model was validated using experimental modal analysis and measured vibrations. The BE model was used to calculate the noise emitted from the pump, and a measurement of sound pressure level at representative field points in a hemianechoic chamber was conducted to validate the BE model. Comparisons between the simulated and measured results show that the developed LP/FE/BE model is effective in capturing the vibroacoustic characteristics of the pump. The presented approach can be extended to other types of fluid power components and contributes to the development of quieter fluid power systems.

Multidisciplinary Design Optimization of a Swash-Plate Axial Piston Pump

This work proposes an MDO (multidisciplinary design optimization) procedure for a swash-plate axial piston pump based on co-simulation and integrated optimization. The integrated hydraulic-mechanical model of the pump is built to reflect its actual performance, and a hydraulic-mechanical co-simulation is conducted through data exchange between different domains. The flow ripple of the pump is optimized by using a MDO procedure. A CFD (Computational Fluid Dynamics) simulation of the pump’s flow field is done, which shows that the hydrodynamic shock of the pump is improved after optimization. To verify the MDO effect, an experimental system is established to test the optimized piston pump. Experimental results show that the simulated and experimental curves are similar. The flow ripple is improved by the MDO procedure. The peak of the pressure curve is lower than before optimization, and the pressure pulsation is reduced by 0.21 MPa, which shows that the pressure pulsation is improved with the decreasing of the flow ripple. Comparing the experimental and simulation results shows that MDO method is effective and feasible in the optimization design of the pump.

Theoretical flow rate in crescent pumps

In this paper, a method for evaluating the kinematic flow rate of a crescent oil pump is presented. The procedure also allows calculating the angular derivatives of the delivery, suction and trapped volumes of the pump, which are the prerequisites for the simulation of the unit using a lumped parameters approach. The method is based on the knowledge of the length of the vector rays between the centres of the gears and the contact points. From the volume derivatives, an analytic expression of the pump displacement and of the kinematic flow ripple index is obtained. Moreover, the same formula can also be applied to external gear machines. Finally, in this study the influence of the number of teeth of the driving and driven gears has been assessed. The increase of the number of teeth of the inner gear is beneficial; both for the reduction of the flow ripple and for the increase of the displacement at equal overall pump size.

Analysis of the flow dynamics characteristics of an axial piston pump based on the computational fluid dynamics method

ABSTRACTTo improve its working performance, the flow ripple characteristics of an axial piston pump were investigated with software which uses computational fluid dynamics (CFD) technology. The simulation accuracy was significantly optimized through the use of the improved compressible fluid model. Flow conditions of the pump were tested using a pump flow ripple test rig, and the simulation results of the CFD model showed good agreement with the experimental data. Additionally, the composition of the flow ripple was analyzed using the improved CFD model, and the results showed that the compression ripple makes up 88% of the flow ripple. The flow dynamics of the piston pump is mainly caused by the pressure difference between the intake and discharge ports of the valve plates and the fluid oil compressibility.

Manufacturing and study on influence of changes in center distance in circle arc-involute-circle arc gear pump operating at high pressure and high speed

This study examined the effect of changes in center distance on a circular-arc gear pump that operates at high pressure and high speed. In principal these types of gear pumps have no trapped-oil and flow ripples. The effect of changes in center distance caused by assembly, machining, radial force and oil film force on the performance of circular-arc gear pumps was studied. The results show that the flow rate, axial force and torque increased linearly with an increase in variables [Formula: see text]. Computer aided manufacturing for ball end milling has been developed to simulate the process of numerical control of the rotors of circular-arc gear pumps. Two methods for assessing interference are provided. The trajectories of the centers of ball end milling for rough and finish machining are simulated.

Flow ripple reduction of an axial piston pump by a combination of cross-angle and pressure relief grooves: Analysis and optimization

This paper investigates the potential of flow ripple reduction of an axial piston pump by a combination of cross-angle and pressure relief grooves. A dynamic model is developed to analyze the pumping dynamics of the pump and validated by experimental results. The effects of cross-angle on the flow ripples in the outlet and inlet ports, and the piston chamber pressure are investigated. The effects of pressure relief grooves on the optimal solutions obtained by a multi-objective optimization method are identified. A sensitivity analysis is performed to investigate the sensitivity of cross-angle to different working conditions. The results reveal that the flow ripples from the optimal solutions are smaller using the cross-angle and pressure relief grooves than those using the cross-angle and ordinary precompression and decompression angles and the cross-angle can be smaller. In addition, when the optimal design is used, the outlet flow ripples sensitivity can be reduced significantly.

Theoretical analysis on flow characteristics of melt gear pump

The relationship between Geometric parameters and theoretical flow of melt gear pump is revealed, providing a theoretical basis to melt gear pump design. The paper has an analysis of meshing movement of melt gear pump on the condition of four different tooth numbers, stack movement law and flow ripple. The regulation of flow pulsation coefficient is researched by MATLAB software. The modulus formula of melt gear pump is proposed, consistent with actual situation.

사판식 피스톤 펌프의 밸브 플레이트 설계와 예압에 따른 맥동

Article history: This study investigated the design factors of the opening area in order to consider the kinematic stability of a valve plate, conducting an analysis of the reduction effects of pressure pulsation and flow ripple depending on the design factors, using the SimulationX Ⓡ (Germany) hydraulic analysis program. Further, we performed a structure analysis to confirm the kinematic stability of the valve plate in a swash plate type piston pump, and analyzed the effects of pulsation on a 1-step V–type notch, 2-step V-type notch, and 2-step U-type notch to determine the effects of pulsation reduction. Finally, we show the effectiveness of our proposed design of the pre-compression sections on a valve plate in terms of low pulsation by using the hydraulic analysis program, SimulationX

Study on flow characteristics and flow ripple reduction schemes of spool valves distributed radial piston pump

This paper studies the flow characteristics and flow ripple reduction techniques of a spool valves distributed radial piston pump. The mathematical models of the pump are established, and simulations based on the mathematics are performed in AMESim environment. The results indicate that the spool valves distributed radial piston pump has fewer flow fluctuations than the pump distributed by check valves, due to the rigid motion of its distribution component—the spool valves. Then, in order to reduce the flow ripple of the spool valves distributed radial piston pump, three techniques, namely, time delay, relief chamfer and transition compression filter volume, are proposed and their working principles are illustrated. Particularly, the design method of time delay is elaborated and its effectiveness is evaluated. The simulation results suggest that with the usage of the time delay method, the fluctuation range of the spool valves distributed radial piston pump is expected to be reduced by 21.7%.

Numerical simulation of low-pulsation gerotor pumps for use in the pharmaceutical industry and in biomedicine

Abstract The reduction of the pulsation of flow and pressure as well as the increase of the mean flow of a displacement pump will be a benefit to many technical processes, especially in the pharmaceutical industry and in biomedicine. By reducing the flow pulsation, microreactors could work more efficiently and thin-film coatings or fluids in biomedical applications could be applied with more precision. This article presents a new toolbox to analyse and compare different types of gerotor pump gear profiles. The main objective was the development of a toolbox to analyse the mean flow and the flow ripple of theoretical and reverse engineered gerotor gear sets. For that reason, the presented toolbox does not work with analytic functions, but with numerical methods based on point cloud data. A comparison of four different profile types shows that these profiles perform very differently if they are limited by a given maximal outer root diameter and by the numbers of the teeth of both rotors.