Numerical investigation of internal flow in hydraulic valves and dynamic interactions in hydraulic systems with CFD and simplified simulation methods

Transkript

1 Numerical investigation of internal flow in hydraulic valves and dynamic interactions in hydraulic systems with CFD and simplified simulation methods Vom Fachbereich Maschinenbau an der Technischen Universität Darmstadt zur Erlangung des Grades eines Doktor-Ingenieurs (Dr.-Ing.) genehmigte D i s s e r t a t i o n vorgelegt von Dipl.-Ing. Qing Chen aus Pingyao, China Berichterstatter: Mitberichterstatter: Prof. Dr.-Ing. B. Stoffel Prof. Dr. rer. nat. M. Schäfer Tag der Einreichung: Tag der mündlichen Prüfung: Darmstadt 2004 D17

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3 Berichte aus der Strömungstechnik Qing Chen Numerical investigation of internal flow in hydraulic valves and dynamic interactions in hydraulic systems with CFD and simplified simulation methods. D 17 (Diss. TU Darmstadt) Gedruckt mit Unterstützung des Deutschen Akademischen Austauschdienstes Shaker Verlag Aachen 2005

4 Bibliographic information published by Die Deutsche Bibliothek Die Deutsche Bibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data is available in the internet at Zugl.: Darmstadt, Techn. Univ., Diss., Copyright Shaker Verlag 2005 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the publishers. Printed in Germany. ISBN ISSN Shaker Verlag GmbH P.O. BOX D Aachen Phone: 0049/2407/ Telefax: 0049/2407/ Internet: info@shaker.de

5 To my parents Xiaoping Li, Lihu Chen, and my son Kaiyuan Hou For all their love and understanding V

6 Preface The on hand dissertation came into being during my work as scientific researcher at Institute of Turbomachinery and Fluid Power at Darmstadt University of Technology. Prof. Dr.-Ing. Bernd Stoffel, chief of the institute, is the first person whom I thank especially sincerely for the encouragement for this thesis, the valuable suggestions in many professional discussions, the constant promotion and understanding, along with the chance to enrich my development stage as engineer in Germany. I would like to give my best and sincere thanks to Prof. Dr. rer. nat. Michael Schäfer, chief of Department of Numerical Methods in Mechanical Engineering at Darmstadt University of Technology, for the acceptance of co-reviewer and the critical review of the thesis. My gratefulness is also brought to all colleagues of our institute, particularly to Dr.-Ing. Gerhard Ludwig, Dipl.-Ing. Christian Beinert, Dipl.-Ing. Matevz Dular, Dipl.-Ing. Jens Rösner and Dipl.-Ing. Christian Schaad, Dipl.-Ing. Miriam Roth and Dipl.-Ing. Valérie Bischof for a multitude of fruitful discussions and assistance. For the extensively grammatical and linguistic correction of this thesis, special thanks to my Chinese friend Dr.-Ing. Yongxing Wang. I should like to express my thankfulness further on to my parents, my brother and my grandparents, who encourage me to study in Germany and give their endless concern and understanding to me. Special thanks to DAAD (Deutscher Akademischer Austausch Dienst, or in English: German Academic Exchange Service), who has created the pre-condition for the accomplishment of this thesis through financial support. Last but not least, I would like to thank Dr.-Ing. Andreas Bootz and Dipl.-Ing. Bernhard Brunn heartily for their assistance in solving the problem of dynamic simulation in the first two years of my staying in Germany. I affirm that I have independently finished the thesis except for the above mentioned promotions and necessary implement. Darmstadt, in November 2004 Qing Chen VI

7 Abstract On the basis of the introduction of theoretical fundamentals, dynamic interactions in hydraulic pipeline systems are studied using different simplified simulation methods. Simulation results of the concentrated parameter method, the distributed parameter method and the transfer matrix method are represented and compared with each other as well with the help of Bode analyses of magnitude and phase in the frequency domain. By flow simulation, the internal flow processes in a hydraulic pressure relief valve and a servo valve are investigated under different calculation conditions with the aid of CFD. The analyses of turbulent flow, the cavitation phenomenon under steady and unsteady condition and dynamic opening and closing process of the pressure relief valve are carried out using the corresponding turbulent-, multiphase- and dynamic meshing model provided in the CFD commercial code FLUENT. Studies of the distributions of various parameters, e.g., static pressure, velocity magnitude, velocity vector and volume fraction of vapor especially for the evaluation of the cavitation are carried out under the corresponding computing conditions. Furthermore, the offline and online coupled simulations of simple hydraulic systems are implemented with the interfaces of 2-Level-S-Function in Matlab/Simulink and UDF (User- Defined-Function) in FLUENT. The principle of the coupled simulation using the model of the distributed parameter-characteristic method and CFD is briefly introduced. In the case of online coupling, the dynamic velocity profile at the inlet of the pressure relief valve, which is obtained by the simulation with the characteristic method, is used as boundary condition for the internal flow analysis with CFD. The online coupled simulation is realized by the assignment of two parallel-working personal computers, which respectively implement CFD calculation and the computation with the characteristic method. The necessary transfer of the signal files is accomplished per TCP/IP to bring the coupled simulation to success. Hereafter, some simulation results are represented to validate the validity of the coupling principle. VII

8 Kurzfassung Basierend auf die Einführung der theoretischen Grundlagen werden dynamische Wechselwirkungen in hydraulischen Systemen untersucht mittels verschiedener vereinfachter Simulationsverfahren. Simulationsergebnisse, die mit der Methode der konzentrierten Parameter, mit dem Charakteristikenverfahren und mit dem Übertragungsmatrizenverfahren erzielt wurden, werden dargestellt und miteinander verglichen an Hand von Bode-Analysen der Größe und der Phase im Frequenz Bereich. Bei Strömungssimulation werden die inneren Strömungsvorgänge in einem Druckbegrenzungsventil und in einem Servoventil unter verschiedenen Berechnungsbedingungen mit Hilfe von CFD untersucht. Es erfolgen Analysen der turbulenten Strömung, des Kavitationsphänomens unter stationärer und instationärer Bedingung und des dynamischen Öffnungs- und Schließvorgangs des Druckbegrenzungsventils unter Verwendung von entsprechenden turbulent, multiphase und dynamic meshing" Modellen, die im kommerziellen CFD- Code FLUENT bereitgestellt sind. Es werden Studien der Verteilungen der unterschiedlichen Parameter, z.b. des statischer Drucks, der Geschwindigkeitsgröße, des Geschwindigkeitsvektors und des Dampfanteils speziell für die Beurteilung der Kavitation durchgeführt unter den entsprechenden Berechnungs-Bedingungen. Darüber hinaus werden online" und "offline" gekoppelte Simulationen für einfache hydraulische Systeme ausgeführt mit dem Interface der 2-Level-S-Function in Matlab/Simulink und UDF (User-Defined-Function) in FLUENT. Das Prinzip der gekoppelten Simulation mit der Methode des Charakteristikenverfahrens und CFD wird kurz eingeführt. Im Falle von online- Koppelung liefert das dynamische Geschwindigkeitsprofil bei der Einströmung zum Druckbegrenzungsventil, das von der Simulation mit dem Charakteristikenverfahren erhalten wird, die Randbedingungen für die Analyse der inneren Strömungen mit CFD. Diese online gekoppelte Simulation wird realisiert durch den Einsatz von zwei parallel betriebenen Personal-Computern, die jeweils die CFD-Berechnungen bzw. die Rechnungen mit dem Charakteristikenverfahren ausführen. Der erforderliche Transfer der Signal-Dateien, um die gekoppelte Simulation zum Erfolg zu bringen, erfolgt mit TCP/IP. Einige Simulationsergebnisse werden präsentiert, um die Gültigkeit des Koppelungsprinzips zu bestätigen. VIII

9 Contents 1 Introduction Objectives and methods Structure State-of-the-art Academic overview of the problem Dynamic pressure change Oscillating and pulsating flow Transient flow Dynamic performance of the pipe flow CFD analysis of flow behavior of hydraulic valves Simulation tools used in fluid technology Simplified modelling techniques Structure analysis with FEM Flow simulation with the aid of CFD Theoretical fundamentals Simplified simulation methods for oil hydraulic systems Model of concentrated parameters Derivation Solution to the system equations Distributed parameters Derivation Solution to the system equations in time domain Approach of wall shear stress Optimization of the friction approach Transfer matrix method CFD numerical calculation Description of turbulent flow Standard k- turbulence model RNG k- turbulence model Mixture multiphase model Continuity equation for the mixture Momentum equation for the mixture Energy equation for the mixture Relative (Slip) velocity and the drift velocity Volume fraction equation for the secondary phases Dynamic mesh model Dynamic mesh conservation equations Dynamic mesh update methods Simulation results of hydraulic systems with simplified modelling methods n-element concentrated parameter element concentrated parameter Comparison of different elements concentrated parameter Characteristic method Comparison of concentrated and distributed parameter Simulation with transfer matrix method Comparison of simulations with different simplified methods IX

10 4.6 Conclusions Turbulent flow and cavitation of a pressure relief valve Turbulent flow Valve with complex seat Valve with simple seat Comparison of simulation results of two simplified configurations Influences of the inlet flow rate Influences of the outlet pressure Cavitation Unsteady cavitation in the valve with complex seat Influences of the inlet flow rate Influences of the outlet pressure Influences of turbulence models Cavitation in the valve with simple seat Steady cavitatin Unsteady cavitation Influence of gap on cavitation Dynamic mesh simulation Opening process of the valve with simple seat Distribution of pressure Distribution of velocity Closing process of the valve with simple seat Static pressure Velocity magnitude Cavitation and closing process of the valve Constant cone motion velocity Vapor volume fraction Static pressure Velocity Sinusoidal cone motion velocity Numerical simulation of a 3D servo valve Geometry and mesh Laminar flow Turbulent flow Cavitation Coupled simulation of whole hydraulic systems Off-line-coupling On-line-coupling Motivation Determination of the coupling modus Formulation of boundary conditions Predefinition and tests Coupling principle Coupling results Summary and outlook Literature X

11 11 Symbols and abbreviations Appendices XI