R. Castilla

An empirical methodology for prediction of shape and flow rate of a free-falling non-submerged liquid and casting iron stream:

The work presented in this article demonstrates the use of an empirical and simplified approach based on an optical technique and a home-made ad hoc code that give knowledge of the shape and falling velocity of a free-falling non-submerged liquid stream to predict its typology and flow rate. The visualization photographic technique is a non-intrusive robust technique which can be applied to high-temperature liquids in harsh environments, such as an iron stream in a foundry. This technique allows predicting the liquid stream boundaries and contours without any type of treatment on the fluid. As a result of employing this empirical methodology, three flow typologies for a water stream are proposed and demonstrated experimentally. Comparisons with experimental data reveal satisfactory estimations of mean flow quantities. Finally, the approach used based on experimental visualization is carried out in an iron stream of a foundry, not being disruptive to in-situ foundry operations and showing its potential to improve performance of the cast parts’ properties during the casting phase and revealing to be a useful tool for process optimization.

Influence of the interteeth clearances on the flow ripple in a gerotor pump for engine lubrication

A gerotor pump, which is widely used in the automotive industry for engine oil lubrication, produces an instantaneous flow fluctuation and the estimation of this is fundamental in order to evaluate the pump quality for silent and smooth operation. The intricate aspects of the pumping process of a gerotor pump make computational fluid dynamics the appropriate tool for modelling and simulation to provide insights into its flow characteristics. Because the instantaneous flow is rather dependent on the teeth contact, a new boundary condition of a virtual wall was developed, which allows simulation of the teeth contact in the interteeth radial clearances. This new boundary condition is utilized in a three-dimensional model of the gerotor pump with mesh deformation and remeshing at every time step by means of a home-made ad-hoc code programmed by the present authors and named viscous wall cell. The code has been integrated into the computational fluid dynamics solver. The interteeth clearances are studied under the following different operating conditions (working pressures and rotational velocities): first, no contact points (no teeth contact is studied in order to prove that, even if the interteeth radial clearance is sufficiently small, the leakage cannot be negligible); second, all contact points (the ideal approach is considered with zero interteeth radial clearances used to model zero manufacturing tolerances); third, one contact point at different locations (the existence of manufacturing tolerances and the teeth contact approach make the pump’s operation and its pumping mechanism more realistic in the simulation). The numerical instantaneous flow is compared with the analytical instantaneous flow, with the instantaneous flow modelled by using the bond graph technique, and with the experimental determination of the flow ripple for a specific unit. The results obtained show the importance of simulating the teeth contact and prove to be an excellent estimation of the instantaneous flow behaviour to obtain the dynamic properties of a gerotor pump under more realistic conditions than its design.

GEROLAB Package System: Innovative Tool to Design a Trochoidal-Gear Pump

An innovative tool for the improvement of the design methodology of a trochoidal gear, which works as a part of a hydraulic pump, is introduced. For the past few years, new, specific, and demanding applications of this type of pumps have demanded to maximize efficiency and to reduce manufacturing costs by improving its two main performance indexes: volumetric characteristics and teeth contact stress. The existing methodologies and software fail to thoroughly address the design by taking into account both performance indexes. The software presented is an integrated package system, which is composed of three basic modules: design, volumetric characteristics, and contact stress module. As a result, by consecutively following each module, this new tool allows to find the better gear set for the concrete initial required design parameters. An application using the GEROLAB package system methodology is carried out to obtain the best candidate, which is compared and contrasted with a gear set of a specific gerotor pump unit. As a conclusion, this new software aims to lead the designer to a better design by improving performance indexes of a new born gerotor pump project.

Numerical Analysis of the Shaft Motion in the Journal Bearing of a Gear Pump

This paper describes a numerical analysis of the dynamics of the shaft in the journal bearing of a gear pump.

Computational fluid dynamics and particle image velocimetry assisted design tools for a new generation of trochoidal gear pumps

Trochoidal gear pumps produce significant flow pulsations that result in pressure pulsations, which interact with the system where they are connected, shortening the life of both the pump and circuit components. The complicated aspects of the operation of a gerotor pump make computational fluid dynamics the proper tool for modelling and simulating its flow characteristics. A three-dimensional model with deforming mesh computational fluid dynamics is presented, including the effects of the manufacturing tolerance and the leakage inside the pump. A new boundary condition is created for the simulation of the solid contact in the interteeth radial clearance. The experimental study of the pump is carried out by means of time-resolved particle image velocimetry, and results are qualitatively evaluated, thanks to the numerical simulation results. Time-resolved particle image velocimetry is developed in order to adapt it to the gerotor pump, and it is proved to be a feasible alternative to obtain the instantaneous flow of the pump in a direct mode, which would allow the determination of geometries that minimize the non-desired flow pulsations. Thus, a new methodology involving computational fluid dynamics and time-resolved particle image velocimetry is presented, which allows the obtaining of the instantaneous flow of the pump in a direct mode without altering its behaviour significantly.

Experimental Study of the Shaft Motion in the Journal Bearing of a Gear Pump

The movement of the shaft of a driven gear in a gear pump is experimentally studied. Three different methods are considered, and the use of a laser micrometer measurement method is validated. In order to use the laser micrometer, some modifications are made to the gear pump. Experimental results for different working pressures and rotational velocities are shown. For a low nondimensional working pressure, defined in a similar way as the Sommerfeld load, experimental and numerical results agree very well for relative eccentricity. Nevertheless, experimental results made clear that the role of the lateral plate of the pump is very important for high nondimensional working pressure. A value of 100 is given for the critical nondimensional working pressure in order to avoid wear and slant in the lateral plate. Frequency analysis of the outlet pressure, as well as the precise measurement of the wear in the pump case, support experimental observation of the inability of the journal to retain the shaft for high nondimensional pressure.

Pressure effects on the performance of external gear pumps under cavitation

The numerical analysis of an external gear pump with cavitation effects has been validated with experimental data obtained by applying Time-Resolved Particle Image Velocimetry. The effect of inlet and outlet pressure on volumetric efficiency has been studied numerically. First, the Particle Image Velocimetry method was used to analyze the two-dimensional velocity field in the middle plane of the suction chamber of the gear pump. The main improvement, with respect to previous similar analysis is the use of alginate micro particles as tracers. It is seen that the two-dimensional model is able to characterize the flow field of the real pump in the region of the inlet chamber in which cavitation is expected. In a previous study, it was seen that a cavitation cloud acted as a virtual contact point at low pressure, being responsible for an increase on the volumetric efficiency. The first set of simulations represents the pump working with high outlet pressure. Now, the cavitation cloud is not present and cavitation no longer helps to improve the efficiency of the pump. The second set of simulations represents the pump with an inlet loss factor, which implies a mean inlet pressure below atmospheric conditions. This allows cavitation clouds to propagate upstream. Despite the larger cavitation clouds, volumetric efficiency only drops at high operating velocities, when some clouds become trapped between gears and casing and are transported to the pressure side.

Methodology based on best practice rules to design a new-born trochoidal gear pump

The trochoidal gear pump, also known as gerotor, owing to its remarkable advantages compared to other hydraulic pumps is chosen for many engineering applications. As each application is unique, the designer ought to be knowledgeable of the required specifications as a first task but need not be an expert in the hydraulic pump design. The review of the existing research reveals significant gaps to develop a new-born project and the work presented in this paper, drawn on existing research work and the authors’ own experience and know-how, aims to overcome them. The objective of the paper is then to provide a summary of the best practice rules to design a trochoidal gear pump from scratch achieving a thorough understanding. In the conceptual stage, making decisions come according to a predetermined set of four parameters known by the designer that will lead to the complete development of the trochoidal gear set. Afterwards, in the design process, the most important characteristics of the pump such as the porting, the pump construction, and the limitations are presented based on the significant explanations, with regard to each feature, selection, effects, and good practices. As a result, the methodology presented compiles the process of engineering in designing a new trochoidal gear pump as a catalogue of guidelines aiming to overcome a vague design due to a lack of knowledge. This collection of best practice rules intends to guide the designer to take good decisions early in the design process that limit design change later in the final stage—the prototype.

Method for Fluid Flow Simulation of a Gerotor Pump using OpenFOAM

A new approach based on the open source tool OpenFOAM is presented for the numerical simulation of a mini gerotor pump working at low pressure. The work is principally focused on the estimation of leakage flow in the clearance disk between pump case and gears. Two main contributions are presented for the performance of the numerical simulation. On one hand, a contact point viscosity model is used for the simulation of solid–solid contact between gears in order to avoid the teeth tip leakage. On the other hand, a new boundary condition has been implemented for the gear mesh points motion in order to keep the mesh quality while moving gears with relative velocity. Arbitrary coupled mesh interface (ACMI) has been used both in the interface between clearance disk in inlet/outlet ports and between clearance disk and interteeth fluid domain. Although the main goal of the work is the development of the numerical method rather than the study of the physical analysis of the pump, results have been compared with experimental measurement and a good agreement in volumetric efficiency and pressure fluctuations has been found. Finally, the leakage flow in the clearance disk has been analyzed.

ESTIMATION OF WALL SHEAR STRESS USING 4D FLOW CARDIOVASCULAR MRI AND COMPUTATIONAL FLUID DYNAMICS

In the last few years, wall shear stress (WSS) has arisen as a new diagnostic indicator in patients with arterial disease. There is a substantial evidence that the WSS plays a significant role, together with hemodynamic indicators, in initiation and progression of the vascular diseases. Estimation of WSS values, therefore, may be of clinical significance and the methods employed for its measurement are crucial for clinical community. Recently, four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) has been widely used in a number of applications for visualization and quantification of blood flow, and although the sensitivity to blood flow measurement has increased, it is not yet able to provide an accurate three-dimensional (3D) WSS distribution. The aim of this work is to evaluate the aortic blood flow features and the associated WSS by the combination of 4D flow cardiovascular magnetic resonance (4D CMR) and computational fluid dynamics technique. In particular, in this work, we used the 4D CMR to obtain the spatial domain and the boundary conditions needed to estimate the WSS within the entire thoracic aorta using computational fluid dynamics. Similar WSS distributions were found for cases simulated. A sensitivity analysis was done to check the accuracy of the method. 4D CMR begins to be a reliable tool to estimate the WSS within the entire thoracic aorta using computational fluid dynamics. The combination of both techniques may provide the ideal tool to help tackle these and other problems related to wall shear estimation.