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Validation of Multiphase Flow Simulations in View of Abrasive Water Jet Cutting

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Validation of Multiphase Flow Simulations in View of Abrasive Water Jet Cutting Research Collection Doctoral Thesis Validation of multiphase flow simulations in view of abrasive water jet cutting Author(s): Reinhardt, Yvonne Publication Date: 2014 Permanent Link: https://doi.org/10.3929/ethz-a-010258434 Rights / License: In Copyright - Non-Commercial Use Permitted This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use. ETH Library Diss. ETH No. 22104 VALIDATION OF MULTIPHASE FLOW SIMULATIONS IN VIEW OF ABRASIVE WATER JET CUTTING A thesis submitted to attain the degree of DOCTOR OF SCIENCES of ETH ZURICH (Dr. sc. ETH Zurich) presented by Yvonne Reinhardt Dipl.-Ing., Universität Stuttgart born on December 12, 1983 citizen of Germany accepted on the recommendation of Prof. Dr. L. Kleiser, examiner Prof. Dr. P. Jenny, co-examiner Dr. A. Haselbacher, co-examiner 2014 Abstract Flows found in nature and industrial applications often consist of multi- ple phases. The behavior of such flows is largely determined by complex interactions between the phases which makes predictions challenging. Especially with respect to industrial applications, gaining a deeper un- derstanding about the behavior of multiphase flows is of high interest. The present work is motivated by the three-phase flow of water, air and particles in the mixing head of abrasive water jet cutting (AWJC) de- vices. We examine separately different flow regimes prevailing within the mixing head by means of numerical simulations. We mainly focus on particle-laden air flow and the flow of high-speed water jets emerging into air and develop two codes within the framework of OpenFOAMr, dpaFoam and wjaFoam. They are based on the incompressible Reynolds- Averaged Navier-Stokes (RANS) equations applying the Eulerian two- fluid approach. The turbulence of the fluid phases is modeled using standard k − " turbulence models. The turbulence of the particle phase is calculated via the granular temperature model. Turbulence modula- tion by particles is accounted for. We investigate turbulence modeling for single-phase round jets to over- come deficiencies of RANS models in simulating round jets. We suggest values for a model coefficient in the "-equation adapted to the three most important nozzle designs used in industry, which are the long pipe nozzle, the smoothly converging nozzle and the sharp-edged nozzle. For wall-bounded particle-laden flows, we suggest a new empirical model to account for turbulence modulation in the four-way coupling regime for predicting turbulence augmentation and attenuation behavior. More- over, the dependency of the fluid velocity profile on mass loading is investigated. Empirical relations for the dependency of the centerline Reynolds number and the wall shear Reynolds number on characteristic parameters of the flow are derived. We validate dpaFoam for particle-laden air flows of wall-bounded and free configurations throughout the one-, two- and four-way coupling regime covering a broad range of values of representative non-dimensional parameters such as the mass loading, the particle Reynolds number, the Stokes number and the ratio of particle to turbulence length scale. wjaFoam is validated for single-phase jets and two-phase jet flows of immiscible fluids. The two validated codes provide an essential basis for future three-dimensional, three-phase simulations of flow processes in the mixing head of AWJC devices. Kurzfassung Die in der Natur und in industriellen Anwendungen vorkommenden Strö- mungen bestehen häufig aus mehreren Phasen. Das Verhalten solcher Strömungen wird zum Grossteil durch komplexe Interaktionen zwischen den Phasen bestimmt, was Vorhersagen schwierig macht. Besonders in Hinblick auf industrielle Anwendungen ist es von grossem Interesse, ein tiefergehendes Verständnis für das Verhalten von Mehrphasenströmun- gen zu erlangen. Die Motivation zu der vorliegenden Arbeit basiert auf der dreiphasi- gen Strömung aus Wasser, Luft und Partikeln in der Mischkammer von Abrasiv-Wasserstrahlschneidanlagen. Mit Hilfe numerischer Simulatio- nen untersuchen wir verschiedene Strömungszustände, die in Teilberei- chen der Mischkammer vorkommen. Wir konzentrieren uns dabei vor allem auf partikelbeladene Luftströmungen und das Verhalten von Hoch- geschwindigkeits-Wasserstrahlen in Luft. Dafür entwickeln wir zwei Co- des im Rahmen von OpenFOAMr, dpaFoam und wjaFoam. Diese ba- sieren auf den inkompressiblen Reynolds-gemittelten Navier-Stokes Glei- chungen (RANS) unter Anwendung des Eulerschen Zweifluid-Ansatzes. Die Turbulenz der Fluidphasen wird mit Hilfe etablierter k - " - Modelle unter Berücksichtigung von Turbulenzmodulation durch Partikel model- liert. Die Turbulenz der Partikelphase wird durch das Granulartempe- ratur-Modell beschrieben. Wir untersuchen die Turbulenzmodellierung von einphasigen runden Frei- strahlen, um deren Simulation mittels des RANS-Ansatzes zu optimie- ren. Wir schlagen jeweils einen modifizierten Wert für einen Modell- koeffizienten der "-Gleichung vor, der für die drei in der Industrie am häufigsten vorkommenden Düsengeometrien am besten geeignet ist. Bei den Düsen handelt es sich um eine Düse bestehend aus einem langen Rohr, eine konische Düse und eine scharfkantige Düse (Staurand). Für partikelbeladene Strömungen, die durch Wände begrenzt sind, entwi- ckeln wir ein neues empirisches Modell, das die Turbulenzmodulation im Bereich der Vierwegekopplung beschreibt, um Turbulenzerhöhung und -reduktion vorherzusagen. Daneben untersuchen wir die Abhängigkeit des Fluidgeschwindigkeitsprofils von der Massenbeladung. Empirische Beziehungen für die Abhängigkeit der mit der Mittengeschwindigkeit ge- bildeten Reynoldszahl und der Wandschubspannungs-Reynoldszahl von charakteristischen Strömungsparametern werden hergeleitet. Wir validieren dpaFoam für partikelbeladene Luftströmungen in offe- nen und wandbegrenzten Konfigurationen im Bereich der Ein-, Zwei- und Vierwegekopplung. Dabei decken wir einen grossen Wertebereich charakteristischer Strömungsparameter wie Massenbeladung, Partikel- Reynoldszahl, Stokeszahl und Verhältnis der Partikel-Längenskala zur turbulenten Längenskala ab. Ebenso validieren wir wjaFoam für die Si- mulation von einphasigen Freistrahlen und zweiphasigen unmischbaren Fluiden im Freistrahl. Die zwei getesteten Codes stellen eine wesentli- che Grundlage zur künftigen dreidimensionalen, dreiphasigen Simulation von Strömungsprozessen in der Mischkammer von Abrasiv-Wasserstrahl- schneidanlagen dar. Acknowledgment I would like to thank Prof. Kleiser for the opportunity to work in his group at the Institute of Fluid Dynamics (IFD), for the possibility to study multiphase flows and for getting insight into teaching matters. I am thankful for his support, his guidance and his interest in multiphase flows over the last years. Likewise I thank Prof. Jenny and Dr. Hasel- bacher for their input, for fruitful discussions and for taking over the task of being my co-examiners. I am grateful for the collaborations with Anna Kubik, Tarun Chadha and Daniel W. Meyer. Stimulating discussions with you and your input have helped me expanding my knowledge and understanding of particle-laden flows. Likewise I thank Stefan Bühler and Tobias Luginsland for giving me insight into jet flows. I greatly acknowledge discussions and support from our OpenFOAM group, especially from Michael Wild, Heng Xiao, Wolfgang Wiedemair, Bernhard Grieser and Adrien Lücker. Special thanks go to my former and current colleagues at IFD who were not only colleagues but also became friends. Whether excited technical discussions, relaxing coffee breaks or private events, sharing my time with you made my life much more colorful! I would like to thank all technical and administrative staff at IFD, espe- cially Bianca Maspero for her help with various administrative matters and Hans Peter Caprez for his IT-support. I thank Werner Müller for his support during my time as assistant of the Fluiddynamik II lecture and for his enthusiasm in creating figures! I also thank all my Bachelor and Master students who contributed to my work with their own projects and who made me learn a lot about supervision and guidance. Finally I would like to express my sincere thanks to my family and friends for their support, their encouragement, their patience and their love! Zürich, September 2014 Yvonne Reinhardt Contents Nomenclature III 1 Introduction 1 1.1 Background . .1 1.1.1 Multiphase flow . .1 1.1.2 Abrasive water jet cutting . .2 1.2 Review of existing studies . 11 1.2.1 Analytical investigations . 11 1.2.2 Experimental investigations . 12 1.2.3 Numerical investigations . 16 1.3 Motivation, focus and outline of thesis . 18 2 Computational modeling and methods 21 2.1 Multiphase flow properties . 21 2.1.1 Particle-laden gas flows . 22 2.1.2 Fluid-fluid jet . 27 2.2 Simulation approach . 31 2.3 Governing equations . 34 2.4 Closure models . 37 2.4.1 Momentum exchange . 37 2.4.2 Effective stresses . 39 2.4.3 Turbulence modeling . 42 2.4.4 Turbulence modulation . 46 2.5 Solver properties . 50 2.5.1 Basic solver algorithm . 50 2.5.2 Discretization and implementation . 52 3 Channel and pipe flow 57 3.1 Simulation setup . 57 3.2 Single-phase flow . 61 3.3 Multiphase flow . 64 3.3.1 Model investigations . 64 3.3.2 Validation results . 77 3.3.3 Summary . 92 3.4 Influence of mass loading . 94 3.4.1 Background and motivation . 94 II Contents ∗ 3.4.2 Effect of dimensionless parameters St, Rep, ρ ... 97 3.4.3 Dependency of ReCL and Reτ on characteristic pa- rameters . 100 3.4.4 Summary . 104 4 Jet flow 105 4.1 General simulation
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