1,721,018 research outputs found
A three dimensional CFD modeling methodology applied to improve hydraulic components performance
No full textIn this paper a three-dimensional CFD methodology to improve the performance of hydraulic components is shown.
The study regardsresearch activities developed during the last two year by the Hydraulic Research Group of the University of Naples Federico II coordinated by the Prof. Adolfo Senatore.
Models were build up with PumpLinx®, a commercial CFD 3D code developed by Simerics Inc.®, that solves numerically the fundamental conservation equations of mass, momentum and energy and includes accurate physical models for turbulence and cavitation.
The paper demonstrate that this methodology may produce a significant improvement of the performance of several different components with an important costs reduction for prototyping phase.
The paper presents results obtained on variable displacement vane pump and on a vane pump power split transmission, both pumps are used for mobile application. Analyzing the results of this paper it is possible to appreciate the transversality of the adopted methodology.
The first analysis is made to avoid cavitation phenomena. The study has regarded the analysis of the forces acting on the pump ring related due by cavitation.
The second study has regarded a new vane pump power split transmission concept developed by a research collaboration between the University of Naples and the University of Minnesota (USA). The goal of this activity is the investigation of the output power of the transmission. Results will be compared with experimental data by the end of 2015 when the prototype will be available.
The flexibility the presented methodology makes this approach very interesting in the Hydraulic field offering the opportunity of solve completely different issues in many applications
Modeling Methodology to Study the Internal Fluid-Dynamic of a Gas Filter
No full textA numerical simulation of the flow in a carbon dioxide filter is shown in this paper. The filter is used in the urea production plant and it is connected to the suction of a compressor. The filter housing has a Tee shaped duct and an internal cartridge with a cylindrical shape. The Tee shape allows the cartridge’s assembly. The external diameter of the duct is bigger than the cartridge reducing the stream area to ensure a good filtration. To simplify the manufacturing process, the first design of the cartridge has 9mm diameter holes distributed in circular and longitudinal pattern. It has 14mm and 8mm center distance in longitudinal side and circular side. The filter has an inlet diameter of 20” and a divergent outlet of 24”. The aim of this study is the analysis and optimization of the filter geometry in terms of total pressure between its inlet and outlet side. Moreover an optimization of the basket’s holes distribution was done. First of all the 2D model of a first filter geometry was compared with a 3D model. The comparison showed a good agreement of results. Then the outlet diameter, the inlet angle and the holes arrangement have been studied with a bi-dimensional CFD modeling approach. The final goal of the whole activity was to introduce a methodology to optimize a very complex geometry by using a simplified bi-dimensional model with low computational costs
A simulation methodology applied on hydraulic valves for high fluxes
No full textA mathematical modeling approach for the study of a directional valve is proposed in this paper. The analyzed valve is a High flow 6-way directional valve, with nominal flow-rate of 2500 l/min and maximum inlet pressure of 26 bar that is used for safety shut down for Power Plants. The final goal is to obtain the best energy efficiency of the valve, request by this specific application. The study is addressed to the design optimization of hydraulic components using a simulation methodology.
The analysis has been performed through a three-dimensional CFD modeling technique by using the commercial code PumpLinx®, developed by Simerics®. This approach allows the study also of particular applications, like the valve analyzed, where the experimentation is complex and expensive with a high reduction of the component’s development phase. This paper is the first part of a research focused on the core design optimization by using a 3D CFD simulation methodology.
With the modeling technique, the flow behavior has been deeply studied by visualizing the pressure, the velocity and the kinetic energy on several valve’s sections. A model for the turbulence has been implemented in the simulation. Several new designs of the valve core have been modeled and the final geometry has achieved the goal of this first part of the study
A modeling approach to study the fluid dynamic forces acting on the spool of a flow control valve
No full textThis paper introduces an approach to study a valve’s internal fluid dynamics. During operation, the flow causes forces on the spool. These forces must be correctly balanced. Since these forces cannot be measured, a three-dimensional (3D) computational fluid dynamic (CFD) modeling approach is needed. A case study has been undertaken to verify the approach on a two-way pressure compensated flow control valve. Since forces vary during operation, the analysis must be transient. From the initial zero spool position, the flow goes through the valve causing a spool shift inside the valve’s housing until the spool stops at its final position. Forces depend on the spring reaction, the inlet pressure force, the pressure force of the fluid inside the spool, and the spring holder volumes, and the balance of forces influences the outlet flow rate at the final spool position. First, the initial case geometry was modeled, prototyped, and tested, and this geometry was studied to verify the model accuracy compared to experimental data. The comparison shows good agreement with a maximum error of 3%. With the same approach, several other geometries were designed, but only the best geometry was prototyped and tested. The model was adopted to make several analyses of velocity contouring, streamlines trends, and pressure distribution in the fluid volume. The modeled and tested results achieved the expected performance confirming the effectiveness of the methodology
Study of a Pump as Turbine for a Hydraulic Urban Network Using a Tridimensional CFD Modeling Methodology
No full textNowadays, the application of a PAT (Pump as Turbine) has been developed in several applications as pressure dropping valve. Generally, pump manufacturers do not provide the characteristic curves of their pump working as turbine and researchers have the objective of build a model to predict the turbine operation of pumps for energy recovery schemes. This paper shows a methodology based on a mathematical model of a centrifugal pump used as a PAT in an urban hydraulic network, to solve this kind of problem. The model was built up, starting from the real geometry, with a commercial tridimensional code, which is particularly suitable to simulate pumps and valves. The aim of this paper isthe investigation on the possibility to use a simulation methodologyto obtain the inverse characteristic of a commercial centrifugal pump. First, the model results were compared with the data declared by the pump manufacturer and after it was used to obtain the inverse characteristic (PAT mode). Furthermore, an experimental test bench was used to obtain the reverse mode pump characteristic, in terms of flowrate/ head. In both cases, the simulation model showed good accuracy, there is a low difference between simulated results and manufacturer/experimental data. The model results, which represents the first step of this activity, revealed that it is possibleto obtain the pump characteristic in reverse mode, which is not declared in the commercial pump datasheet
Numerical analysis and experimental validation of Gerotor pumps: A comparison between a lumped parameter and a computational fluid dynamics-based approach
No full textIn this paper, two alternative numerical approaches for the simulation of Gerotor units are compared: a fast lumped parameter approach for the fluid dynamics through the unit that permits the co-simulation of the radial micro-motion of the rotors, and a computational fluid dynamics approach that puts emphasis on the description of the detailed features of the flow through the unit. Each approach provides unique insights on the unit operation, although with different assumptions and level of result details. For an objective comparison of these two state-of-art models, the authors compared
their results with experiments. A commercial pump taken as reference, and tests focused on steady-state volumetric performance as well as the transient features of the outlet port pressure oscillations. The results presented in the paper permit to gain a high level of understanding of the operation of the unit and of the critical aspects that a designer should consider while analyzing such design of positive displacement machines. While comparing the two simulation approaches, the paper highlights the limits and the strengths of each one of the two approaches. In particular, it is shown how both models can match the experimental results considering proper assumptions, in terms of technological clearances and
rotors’ micro-motions.
The paper constitutes a unique contribution in the field of numerical simulation of Gerotor units and represents a useful reference to the designers looking for suitable methods for simulating existing or novel design solutions
GEROTOR PUMP CAVITATION MONITORING AND FAULT DIAGNOSIS USING VIBRATION ANALYSIS THROUGH THE EMPLOYMENT OF AUTO-REGRESSIVE-MOVING-AVERAGE TECHNIQUE
No full textGerotor pumps, as well known, are widely used in lubrication circuits of internal combus- tion engines for their simplicity, high efficiency and low costs. In this paper an experimental characterization of a Gerotor pump is shown. The re- search is a collaboration between the Hydraulic Power Research Group (HPRG) of the Uni- versity of Naples “Federico II”and the Istituto Motori of CNR. The aim of this research is to investigate the possibility of using simple data to acquire, as vibrational data, on the pump under investigation to detect possible cavitation problem by implementing a proper mathematical procedure to this aim. As been demonstrated that these pumps are particularly subject to cavitation. The gerotor pumps are much subject to cavitate than expected, especially under par- ticular operating conditions of the engine. Cavitation is also correlate to vehicle dynamics particularly with the recent tendency to reduce the mass of oil in the sump. Therefore, the research to avoid cavitation is crucial nowadays. Consequently this study has been firstly performed with an experimentation on the pump by monitoring the delivered oil flow-rate and the adsorbed torque on the pump shaft. An accurate analysis of the pressure oscilla- tions in cavitation conditions, has been, also, conducted. Then, an accelerometer sensor has been properly located to study the cavitation with a fault diagnosis system based on vibration detection. The experimental tests have been performed on a test bench of the Hydraulic Labora- tory of the University of Naples “Federico II”in Italy. The bench allows testing the pump working by varying the shaft speed, the oil temperature, the suction and the delivery pres- sure. The main measured parameters are shaft torque, oil flow rate, mean suction and de- livery pressure and the instantaneous suction and delivery pressure. As expected, tests revealed the high influence of the suction pressure on the deliv- ered oil flow rate, while no significant influence has been noted on the adsorbed torque. Furthermore, the pressure oscillations in the pump delivery are highly influenced by the suction pressure. A non intrusive accelerometer has been installed during the experimentation on the oil pump. Since the vibration due to cavitation is the main concern of this study, the ac- celerometer has been mounted at the suction port in the radial direction.
More precisely, the paper presents a fault diagnosis system based on vibration detec- tion. Firstly, a Fast Fourier Transform of the vibration signal has been computed. The in- vestigation has been made with and without the presence of cavitation varying the pump rotation speeds. Limitations due to the detecting of the on line cavitation problems by monitoring the FFT vibration spectra have been overcame by implementing an alternative method based on stochastic approach. This diagnosis method of accelerometer time series analysis based on an Auto Regres- sive and Moving Average (ARMA) method has been used to determine the pump failure. The diagnosis results have demonstrated the ability of the proposed mathematical tech- nique in the identification of cavitation phenomena proving that the proposed approach is a useful methodology to detect the presence of fault. The approach can predict, with good accuracy, pump failure in real time operation. In addition, a threshold vibration level in decibel scale is also fixed
Study of a proportional spool valve noise by means of Functional Data Analysis: Cavitation and intensity detection
No full textCavitation inside hydraulic components is a well-known issue, that arises under specific operating conditions. When this phenomenon occurs in valves, it leads to several issues, such as materials damage, performance reduction, and noise. The latter of them is becoming increasingly important in the transport sector, which is moving towards new technologies (i.e., electrification) that are notoriously quiet. Therefore, cavitation detection is becoming a matter of interest for several applications. The purpose of the work presented is to develop a diagnostic technique to detect the onset of cavitation in proportional valves. A 2-way 2-position proportional spool valve has been placed inside an acoustic enclosure; noise signals have been recorded by means of a high frequency microphone, for different flow rates and valve openings. Sound pressure levels have been analysed by means of statistical techniques; a Functional Data Analysis (FDA) has been performed in the open-source R environment, in which the experimental data, collected under different non-cavitation conditions, have been firstly used to perform a Functional Principal Component Analysis (FPCA) and then to define a threshold. Then, a further experimental dataset has been evaluated through a Hotelling control chart, from which it is possible to distinguish cavitating conditions as they fall outside the limits
A Mathematical Model to Analyze the Torque Caused by Fluid-Solid Interaction on a Hydraulic Valve
No full textIn this paper, a three-dimensional (3D) computational fluid dynamics (CFD) methodology to improve the performance of hydraulic components will be shown, highlighting the importance that a study in the fluid mechanics field has for their optimization. As known, the valve internal geometry influences proportional spool valve hydraulic performance, axial flow forces, and spin effects on the spool. Axial flow forces and spin effects interact directly with the position control performance of a direct actuating closed-loop control valve, reducing its capability. The goal of this activity is the study of the torque on the spool induced by the flow and using a CFD 3D methodology to identify causes of this phenomenon and to find a general mathematical solution to minimize the spool spin effect. The baseline configuration and the new ones of the proportional four-way threeposition closed-loop control spool valve have been studied with a mathematical model. The models were also validated by the experimental data performed in the Hydraulic Lab of the University of Naples. In particular, the tests allowed to measure the torque on the spool varying the oil flow rate, using a dedicated test bench layout where the spool was directly connected to a torque meter. Several geometries have been analyzed to find the best one to minimize spool spin behavior while maintaining an acceptable pressure drop. The study results confirmed the significant improvement of overall component performance
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