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  • Numerical simulation of multiphase immiscible flow on unstructured meshes

     Jofre Cruanyes, Lluís
    Defense's date: 2014-07-25
    Department of Heat Engines, Universitat Politècnica de Catalunya
    Theses

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    Aquesta tesi té com a objectiu desenvolupar una base per a la simulació numèrica de fluids multi-fase immiscibles. Aquesta estratègia, encara que limitada per la potència computacional dels computadors actuals, és potencialment molt important, ja que la majoria de la fenomenologia d'aquests fluids sovint passa en escales temporals i especials on les tècniques experimentals no poden ser utilitzades. En particular, aquest treball es centra en desenvolupar discretitzacions numèriques aptes per a malles no-estructurades en tres dimensions (3-D). En detall, el primer capítol delimita els casos multifásics considerats al cas en que els components són fluids immiscibles. En particular, la tesi es centra en aquells casos en que dos o més fluids diferents són separats per interfases, i per tant, corresponentment anomenats fluxos separats. A més a més, un cop el tipus de flux es determinat, el capítol introdueix les característiques físiques i els models disponibles per predir el seu comportament, així com també la formulació matemàtica i les tècniques numèriques desenvolupades en aquesta tesi.El segon capítol introdueix i analitza un nou mètode ¿Volume-of-Fluid¿ (VOF) apte per a capturar interfases en malles Cartesianes i no-estructurades 3-D. El mètode reconstrueix les interfases com aproximacions ¿piecewise planar approximations¿ (PLIC) de primer i segon ordre, i advecciona els volums amb un algoritme geomètric ¿unsplit Lagrangian-Eulerian¿ (LE) basat en construïr els poliedres a partir de les velocitats dels vèrtexs de les celdes. D'aquesta manera, les situacions de sobre-solapament entre poliedres són minimitzades.Complementant el capítol anterior, el tercer proposa una estratègia de paral·lelització pel mètode VOF. L'obstacle principal és que els costos computacionals estan concentrats en les celdes de l'interfase entre fluids. En conseqüència, si la interfase no està ben distribuïda, les estratègies de ¿domain decomposition¿ (DD) resulten en distribucions de càrrega desequilibrades. Per tant, la nova estratègia està basada en un procés de balanceig de càrrega complementària a la DD. La seva eficiència en paral·lel ha sigut analitzada utilitzant fins a 1024 CPU-cores, i els resultats obtinguts mostren uns guanys respecte l'estratègia DD de fins a 12x, depenent del tamany de la interfase i de la distribució inicial.El quart capítol descriu la discretització de les equacions de Navier-Stokes per a una sola fase, per després estendre-ho al cas multi-fase. Una de les característiques més importants dels esquemes de discretització, a part de la precisió, és la seva capacitat per conservar discretament l'energia cinètica, específicament en el cas de fluxos turbulents. Per tant, aquest capítol analitza la precisió i propietats de conservació de dos esquemes de malla diferents: ¿collocated¿ i ¿staggered¿.L'extensió dels esquemes de malla aptes per els casos de una sola fase als casos multi-fase es desenvolupa en el cinquè capítol. En particular, així com en el cas de la simulació de la turbulència les tècniques numèriques han evolucionat per a preservar discretament massa, moment i energia cinètica, els esquemes de malla per a la discretització de fluxos multi-fase han evolucionat per millorar la seva estabilitat i robustesa. Per lo tant, aquest capítol presenta i analitza dos discretitzacions de malla ¿collocated¿ i ¿staggered¿ particulars, aptes per simular fluxos multi-fase, que afavoreixen la conservació discreta de massa, moment i energia cinètica.Finalment, el capítol sis simula numèricament la inestabilitat de Richtmyer-Meshkov (RM) de dos fluids immiscibles i incompressibles. Aquest capítol es una prova general dels mètodes numèrics desenvolupats al llarg de la tesi. En particular, la inestabilitat ha sigut simulada mitjançant un mètode VOF i un esquema de malla ¿staggered¿. Els resultats numèrics corresponents han demostrat la capacitat del sistema discret en obtenir bons resultats per la inestabilitat RM.

  • Conservation properties of unstructured finite-volume mesh schemes for the Navier-Stokes equations

     Jofre Cruanyes, Lluís; Lehmkuhl Barba, Oriol; Ventosa Molina, Jordi; Trias Miquel, Francesc Xavier; Oliva Llena, Asensio
    Numerical heat transfer. Part B, fundamentals
    Date of publication: 2013-11-09
    Journal article

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    The Navier-Stokes equations describe fluid flow by conserving mass and momentum. There are two main mesh discretizations for the computation of these equations, the collocated and staggered schemes. Collocated schemes locate the velocity field at the same grid points as the pressure one, while staggered discretizations locate variables at different points within the mesh. One of the most important characteristic of the discretization schemes, aside from accuracy, is their capacity to discretely conserve kinetic energy, specially when solving turbulent flow. Hence, this work analyzes the accuracy and conservation properties of two particular collocated and staggered schemes by solving various problems.

  • Parallelization strategy for the Volume-of-Fluid method on unstructured meshes

     Borrell, Ricard; Jofre Cruanyes, Lluís; Lehmkuhl Barba, Oriol; Castro Gonzalez, Jesus
    International Conference on Parallel Computational Fluid Dynamics
    Presentation of work at congresses

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    The Volume-of-Fluid (VOF) is one of the most widely used methods for interface tracking in the simulation of multi-fluid flows. The interface between different fluids is generated from the volume fraction scalar fields, which account for the ratio of volume of each fluid in each control volume. Then, an advection equation is solved to obtain the new distribution of the fluids after momentum is applied. Since this is a time-consuming process, parallelization techniques play an essential role. In the VOF approaches most of computing cost of the algorithm is concentrated in operations with the cells that form the interface, i.e. the cells in which coexist different fluids. When the interface is not homogeneously distributed throughout the domain, the standard domain decomposition strategy results in an unbalanced partition. A possible strategy to overcome this limitation is to adapt the domain decomposition to the interface distribution, however, this approach presents a number of drawbacks mainly related to the dynamic location of the interface. In this paper a new strategy, based in a load balancing process complementary to the domain decomposition, is presented with the aim to overcome the limitations of standard domain decomposition based approaches.

  • Numerical simulation of incompressible two phase flows by conservative level set method

     Balcazar Arciniega, Nestor Vinicio; Jofre Cruanyes, Lluís; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; Castro Gonzalez, Jesus
    Conference on Modelling Fluid Flow
    Presentation's date: 2012-09-04
    Presentation of work at congresses

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    Numerical study of the incompressible Richtmyer-Meshkov instability. Interface tracking methods on general meshes  Open access

     Balcazar Arciniega, Nestor Vinicio; Jofre Cruanyes, Lluís; Lehmkuhl Barba, Oriol; Castro Gonzalez, Jesus; Oliva Llena, Asensio
    Conference on Modelling Fluid Flow
    Presentation's date: 2012-09-04
    Presentation of work at congresses

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    The numerical simulation of interfacial and free surface flows is a vast and interesting topic in the areas of engineering and fundamental physics, such as the study of liquid-gas interfaces, formation of droplets, bubbles and sprays, combustion problems with liquid and gas reagents, study of wave motion and others. Many different methods for interface tracking exist, but Volume-of-Fluid and Level-Set methods are two of the most important. The Volume-of-Fluid preserves mass in a natural way but requires large computational resources. On the other hand, the Level-Set is not as accurate and mass conservative as the Volume-of-Fluid but is a faster way to track interfaces, representing them by the middle contour of a signed distance function. The objective of this work is to analyze the advantatges and drawbacks of the Volume-of-Fluid and Level-Set methods by solving the incompressible two-liquid Richtmyer-Meshkov instability and to compare the results to experimental data.

  • Conservation properties and accuracy of unstructured mesh schemes for the Navier Stokes equations

     Jofre Cruanyes, Lluís; Lehmkuhl Barba, Oriol; Ventosa Molina, Jordi; Oliva Llena, Asensio
    International Symposium on Turbulence, Heat and Mass Transfer
    Presentation's date: 2012-09-26
    Presentation of work at congresses

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  • Parallelization of the Volume-of-Fluid method for 3D unstructured meshes

     Jofre Cruanyes, Lluís; Borrell Pol, Ricard; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
    International Conference on Parallel Computational Fluid Dynamics
    Presentation's date: 2012-05-23
    Presentation of work at congresses

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  • VOF/Navier-Stokes implementation on 3D unstructured staggered meshes. Application to the Richtmyer-Meshkov instability

     Jofre Cruanyes, Lluís; Lehmkuhl Barba, Oriol; Castro Gonzalez, Jesus; Oliva Llena, Asensio
    International Conference on Computational Heat and Mass Transfer
    Presentation's date: 2011-07-18
    Presentation of work at congresses

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    The numerical simulation of interfacial and free surface flows is a vast and interesting topic in the areas of engineering and fundamental physics, such as the study of liquid-gas interfaces, formation of droplets, bubbles and sprays, combustion problems with liquid and gas reagents, study of wave motion and others. One of the most powerful and robust methods for interface tracking on fixed grids is the Volume-of-Fluid (VOF). This method tracks the interface between different fluids by evolving the volume fraction scalar field, ratio of fluid to total volume, in time. First, the interface geometry is reconstructed from local volume fraction data. Then, the interface reconstruction and the solution of the Navier-Stokes equations are used to solve the volume fraction advection equation. The objective of this work is to implement a fast, accurate and parallelizable VOF/Navier-Stokes model well suited to 3D unstructured staggered meshes. The interface will be reconstructed by a PLIC method and the advection step will be computed by the means of an unsplit-advection volume tracking algorithm. On the other hand, the Navier- Stokes equations will be solved using an unstructured staggered formulation. The VOF/Navier-Stokes implementation will be tested by comparing the solution of the Richtmyer-Meshkov instability (RMI) to experimental results. The Richtmyer-Meshkov instability occurs at a nearly planar interface separating two fluids that are impulsively accelerated in the direction normal to the interface. This impulsive acceleration can be the result of an impulsive body force or a passing shock wave.

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    Parallelization study of a VOF/Navier-Stokes model for 3D unstructured staggered meshes  Open access

     Jofre Cruanyes, Lluís; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Castro Gonzalez, Jesus; Oliva Llena, Asensio
    International Conference on Parallel Computational Fluid Dynamics
    Presentation's date: 2011-05-16
    Presentation of work at congresses

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    The numerical simulation of interfacial and free surface flows is a vast and interesting topic in the areas of engineering and fundamental physics, such as the study of liquid-gas interfaces, formation of droplets, bubbles and sprays, combustion problems with liquid and gas reagents, study of wave motion and others. One of the most powerful and robust methods for interface tracking on fixed grids is the Volume-of-Fluid (VOF). This method tracks the interface between different fluids by evolving the volume fraction scalar field, ratio of fluid to total volume, in time. First, the interface geometry is reconstructed from local volume fraction data. Then, the interface reconstruction and the solution of the Navier-Stokes equations are used to compute the volume fraction advection equation. The objective of this work is to implement a fast, accurate and efficiently parallelizated VOF/Navier-Stokes model well suited to 3D unstructured staggered meshes. The interface will be reconstructed by a PLIC method and the advection step will be computed by the means of an unsplit-advection volume tracking algorithm. On the other hand, the Navier-Stokes equations will be solved using an unstructured staggered formulation. The parallelization of the VOF/Navier-Stokes model will be studied by solving the Richtmyer-Meshkov instability (RMI). The Richtmyer-Meshkov instability occurs at a nearly planar interface separating two fluids that are impulsively accelerated in the direction normal to the interface. This impulsive acceleration can be the result of an impulsive body force or a passing shock wave.

    Postprint (author’s final draft)

  • A PLIC-VOF implementation on parallel 3D unstructured meshes

     Jofre Cruanyes, Lluís; Lehmkuhl Barba, Oriol; Castro Gonzalez, Jesus; Oliva Llena, Asensio
    European Conference on Computational Fluid Dynamics
    Presentation's date: 2010-06-14
    Presentation of work at congresses

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    The numerical simulation of interfacial and free surface ows is a vast and interesting topic in the areas of engineering and fundamental physics, such as the study of liquid-gas interfaces, formation of droplets, bubbles and sprays, combustion problems with liquid and gas reagents, study of wave motion and others. One of the most powerful and robust methods for interface simulation in xed grids is the Volume-of-Fluid (VOF). In this method, the fluids are represented by a scalar fi eld Ck, known as volume fraction, that represents the portion of volume lled with fluid k. Given a velocity fi eld, interfaces are then tracked by evolving fluid volumes in time. At any time in the solution, an exact interface location is not known. Interface geometry is instead inferred (based on assumptions of the particular algorithm) and its location is reconstructed from local volume fraction data (Interface Reconstruction). The reconstructed interface is then used to compute the volume fluxes necessary for the convective terms in the volume evolution equation (Advection). The objective of this work is to implement a fast, accurate and parallelizable VOF method well suited to 3D unstructured meshes. The selected interface reconstruction algorithms will be the Youngs' (fi rst order) and the LVIRA (second order). In the other hand, the advection step will be computed by the means of an unsplit-advection volume tracking algorithm. In the paper, the VOF method will be tested for different test problems. First, a study of reconstruction accuracy, it is most easily assessed by analyzing the reconstruction of known geometries, such as a hollowed sphere. Second, a rotation test, where a velocity field is imposed and the advection algorithm is tested.

  • IN SPACE PROPULSION-1

     Morales Ruiz, Sergio; Jofre Cruanyes, Lluís; Oliva Llena, Asensio; Perez Segarra, Carlos David; Castro Gonzalez, Jesus
    Participation in a competitive project

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