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  • Large eddy simulations (LES) on the flow and heat transfer in a wall-bounded pin matrix

     Paniagua Sánchez, Leslye; Lehmkuhl Barba, Oriol; Oliet Casasayas, Carles; Perez Segarra, Carlos David
    Numerical heat transfer. Part B, fundamentals
    Vol. 65, num. 2, p. 103-128
    DOI: 10.1080/10407790.2013.846712
    Date of publication: 2014-02-01
    Journal article

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    In this article, the three-dimensional turbulent forced convection in a matrix of wall-bounded 8 × 8 cylindrical pins is studied. Large eddy simulations (LES) are performed for Reynolds numbers 3,000, 10,000 and 30,000. Three different subgrid-scale (SGS) models (WALE, QR, and VMS) are compared on a row-by-row study. Local values of velocity and pressure coefficient are depicted. Turbulence characteristics of the flow are well illustrated. The thermal field is analyzed and validated with the time-averaged Nusselt number at the end walls of the pin matrix. The capabilities of the methodology for predicting the turbulent flow features is also shown.

  • Thermocline thermal storage systems for concentrated solar power plants: one-dimensional numerical model and comparative analysis

     Modi, Anish; Perez Segarra, Carlos David
    Solar energy
    Vol. 100, p. 84-93
    DOI: 10.1016/j.solener.2013.11.033
    Date of publication: 2014-02-01
    Journal article

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    Concentrated solar power plants have attracted increasing interest from researchers and governments all over the world in recent years. An important part of these plants is the storage system which improves dispatchability and makes the plant more reliable. In this paper, a one-dimensional transient mathematical model for a single-tank thermocline thermal energy storage system is presented. The model used temperature dependent correlations to obtain the thermophysical properties for the heat transfer fluid and considered heat loss through the tank wall. The effect of variation in important system parameters like the type of heat transfer fluid, the storage temperature difference and the cycle cut-off criterion on system performance was investigated. The results suggest that two important aspects for assessing the performance of the system are the cyclic behaviour of the system and the time required to attain equilibrium conditions. These aspects directly influence the discharge capacity and discharge power of the storage system, and therefore play an essential role in understanding the start-up characteristics of the system and provide an insight regarding the availability of storage when designing the power cycle for concentrated solar power applications. It was also observed that the cycle durations and the time required to attain cyclic conditions are highly sensitive to not only the storage temperature difference, but also the cut-off temperature difference.

  • Symmetry-preserving discretization of Navier-Stokes equations on collocated unstructured meshes

     Trias Miquel, Francesc Xavier; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio; Perez Segarra, Carlos David; Verstappen, R.W.C.P.
    Journal of computational physics
    Vol. 258, p. 246-267
    DOI: 10.1016/j.jcp.2013.10.031
    Date of publication: 2014-02-01
    Journal article

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    A fully-conservative discretization is presented in this paper. The same principles followed by Verstappen and Veldman (2003) are generalized for unstructured meshes. Here, a collocated-mesh scheme is preferred over a staggered one due to its simpler form for such meshes. The basic idea behind this approach remains the same: mimicking the crucial symmetry properties of the underlying differential operators, i.e., the convective operator is approximated by a skew-symmetric matrix and the diffusive operator by a symmetric, positive-definite matrix. A novel approach to eliminate the checkerboard spurious modes without introducing any non-physical dissipation is proposed. To do so, a fully-conservative regularization of the convective term is used. The supraconvergence of the method is numerically showed and the treatment of boundary conditions is discussed. Finally, the new discretization method is successfully tested for a buoyancy-driven turbulent flow in a differentially heated cavity.

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    Influence of rotation on the flow over cylinder at RE=5000  Open access

     Aljure Osorio, David E.; Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Perez Segarra, Carlos David; Oliva Llena, Asensio
    International ERCOFTAC Symposium on Engineering Turbulence Modelling and Measurements
    Presentation's date: 2014-09-19
    Presentation of work at congresses

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  • Numerical modeling and experimental validation of encapsulated PCM thermal energy storage tanks for concentrated solar power plants

     Galione Klot, Pedro Andres; Perez Segarra, Carlos David; Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; Oliva Llena, Asensio
    Eurotherm Seminar
    Presentation's date: 2014-05-29
    Presentation of work at congresses

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    A numerical simulation model of thermal energy storage systems with encapsulated PCM is presented. In previous papers (Galione et al., 2011), the performance of cylindrical containers filled with PCM spheres and liquid fluids occupying the rest of the space was studied. Different charging and discharging processes were not only numerically analyzed, but also experimentally tested. Based on these numerical simulation tools for predicting the thermal and fluid dynamic behavior of these systems, new PCM tanks built in different solid filled materials and encapsulated PCMs combined into multi-layer storage with molted salt as heat transfer fluid are here presented. A virtual prototype proposed is numerically analyzed, while performance behavior is presented under different devices (charging and discharging conditions, PCMs temperatures, and multilayer configurations). The efficiency of these new configurations is also compared against conventional thermocline, showing the better option depending on cases and/or plants proposed.

  • Improved semi-analytical method for air curtains prediction

     Giraldez Garcia, Hector; Perez Segarra, Carlos David; Rodriguez Pérez, Ivette Maria; Oliva Llena, Asensio
    Energy and buildings
    Vol. 66, p. 258-266
    DOI: 10.1016/j.enbuild.2013.07.011
    Date of publication: 2013-11
    Journal article

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    The present study is devoted to the analysis and prediction of the efficiency of air curtains. The attention is focused on improving existing semi-analytical methods with the information from CFD simulations and experimental measurements. The goal is to obtain an accurate simplified model which describes the three-dimensional behaviour of the air jet without requiring large time consuming calculations. The interaction of the air curtain with other agents, e.g. pedestrians and flying insects, is also revised. The model is validated against both experimental data and advanced LES calculations carried out by the authors. Furthermore, a parametric study shows the air curtain behaviour for different configurations.

  • On the large-eddy simulations for the flow around aerodynamic profiles using unstructured grids

     Lehmkuhl Barba, Oriol; Rodriguez Pérez, Ivette Maria; Baez Vidal, Aleix; Oliva Llena, Asensio; Perez Segarra, Carlos David
    Computers and fluids
    Vol. 84, p. 176-189
    DOI: 10.1016/j.compfluid.2013.06.002
    Date of publication: 2013-09-15
    Journal article

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    This paper investigates the capabilities of two subgrid-scale (SGS) models suitable for unstructured grids for predicting the complex flow in transitional separated bubbles. The flow over a NACA 0012 airfoil at Reynolds number Re = 5e4 and angles of attack (AOA) AOA = 5° and 8° is here considered. The SGS models investigated are: the wall-adapting eddy viscosity model within a variational multiscale method (VMS-WALE) and the QR eddy-viscosity model. Both are well suited for large-eddy simulations (LES) in complex geometries with unstructured grids. The models are assessed and compared to the results of direct numerical simulations (DNS) on the basis of first and second order statistics. Based on the good results obtained, specially with the VMS-WALE model, challenging simulations at high Reynolds numbers and various AOA are also performed. It has been found that predictions of the lift and drag coefficients agree reasonably well with experimental data.

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    Modular object-oriented methodology for the resolution of molten salt storage tanks for CSP plants  Open access

     Rodriguez Pérez, Ivette Maria; Perez Segarra, Carlos David; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
    Applied energy
    Vol. 109, p. 402-414
    DOI: 10.1016/j.apenergy.2012.11.008
    Date of publication: 2013-09
    Journal article

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    Two-tank molten salt storages are the most widespread thermal energy storage technology within concentrated solar power plants. In spite of this, there are design aspects such as thermal losses control, optimisation of the storage or how these devices scale up with the increase in power capacity of the plant which still should be considered. In this sense, numerical modelling of these systems can be a powerful tool for reducing their cost. The present work aims at modelling molten salt tanks by proposing a parallel modular object-oriented methodology which considers the different elements of the storage (e.g. tank walls, insulation material, tank foundation, molten salt storage media, etc.) as independent systems. Each of these elements can be solved independently and using different levels of modelling (from global to fully three-dimensional models), while at the same time they are linked to each other through their boundary conditions. The mathematical models used, together with some illustrative examples of the application of the proposed methodology, are presented and discussed in detail.

  • DNS and regularization modeling of a turbulent differentially heated cavity of aspect ratio 5

     Trias Miquel, Francesc Xavier; Gorobets, Andrei; Perez Segarra, Carlos David; Oliva Llena, Asensio
    International journal of heat and mass transfer
    Vol. 57, num. 1, p. 171-182
    DOI: 10.1016/j.ijheatmasstransfer.2012.09.064
    Date of publication: 2013-01-15
    Journal article

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  • Acumulador de energía térmica en base a materiales de cambio de fase sólido-líquido y método de fabricación de la unidad

     Oliva Llena, Asensio; Perez Segarra, Carlos David; Rigola Serrano, Joaquim; Castro Gonzalez, Jesus; Oliet Casasayas, Carles; Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Trias Miquel, Francesc Xavier; Capdevila Paramio, Roser; Alba Queipo, Ramiro; Ordoño Martinez, Manuel Miguel; Morales Ruiz, Sergio
    Date of request: 2013-03-01
    Invention patent

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  • Máquina de absorción refrigerada por aire

     Oliva Llena, Asensio; Perez Segarra, Carlos David; Rigola Serrano, Joaquim; Castro Gonzalez, Jesus; Oliet Casasayas, Carles; Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Trias Miquel, Francesc Xavier; Capdevila Paramio, Roser; Alba Queipo, Ramiro; Ordoño Martinez, Manuel Miguel; Farnos Baulenas, Joan
    Date of request: 2013-06-14
    Invention patent

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  • Large eddy simulation model assessment of the turbulent flow through dynamic compressor valves

     Estruch Perez, Olga; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; Oliva Llena, Asensio; Perez Segarra, Carlos David
    International Conference on Compressors and Coolants
    Presentation's date: 2013-09-03
    Presentation of work at congresses

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    The present paper attempts the dynamic simulation of the fluid flow through the valve reed taking into account valve movement due to piston displacement. This work widens previous studies based on numerical experiments with static geometry and constant boundary conditions. Hence, in this work attends the newly in-house implemented CFD and moving mesh coupled code TermoFluids. The CFD solver consists of a three-dimensional explicit finite volume fractional-step algorithm formulated in a second-order, conservative and collocated unstructured grid arrangement. Large eddy simulation is performed to solve the turbulent flow, using the subgrid scale WALE model. A radial basis function interpolation procedure is used to dynamically move the mesh according with the displacement of the valve. A simplified geometry of an axial hole plus a radial diffuser with a piston based inlet condition is considered. The valve dynamics is assumed to be given by a law according modal analysis of valve reed.

  • Large eddy simulation of a turbulent jet diffusion flame using the Flamelet-Progress Variable model

     Lehmkuhl Barba, Oriol; Ventosa Molina, Jordi; Perez Segarra, Carlos David; Oliva Llena, Asensio
    European Combustion Meeting
    Presentation's date: 2013-06
    Presentation of work at congresses

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    In this work an hydrogen enriched methane flame in a non-premixed configuration is studied, which corresponds to the DLR flame A. Large Eddy Simulation (LES) will be used to numerically analyse the case. Unstructured meshes are used and coupled with conservative discretisations of the differential operators. Chemical kinetics are modelled using the Flamelet/Progress-Variable model, taking into account differential diffusion effects. Computed first and second moments of the transported variables are shown to be in agreement with the experimental data.

  • Large eddy simulation of a turbulent jet diffusion flame using unstructured meshes

     Muela Castro, Jordi; Ventosa Molina, Jordi; Lehmkuhl Barba, Oriol; Perez Segarra, Carlos David; Oliva Llena, Asensio
    Mediterranean Combustion Symposium
    Presentation's date: 2013-09
    Presentation of work at congresses

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    In this work an hydrogen enriched methane flame in a non-premixed configuration is studied, which corresponds to the DLR flame A. Large Eddy Simulation (LES) will be used to numerically analyse the case. Unstructured meshes are used and coupled with conservative discretisations of the differential operators. Chemical kinetics are modelled using the Flamelet/Progress-Variable model, taking into account differential diffusion effects. Computed first and second moments of the transported variables are shown to be in agreement with the experimental data.

  • Parallel large eddy simulations of wind farms with the actuator line method

     Baez Vidal, Aleix; Lehmkuhl Barba, Oriol; Martinez Valdivieso, Daniel; Perez Segarra, Carlos David
    International Conference on Parallel Computational Fluid Dynamics
    p. 227-232
    Presentation's date: 2013-05-21
    Presentation of work at congresses

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    Parallel Computation of wind farm Large Eddy Simulations (LES) requires the use of with Wind Turbine Models (WTM). CFD and WTM demand different domain decompositions as optimal CFD and WTM decompositions do not necessarily coincide. Nevertheless, data exchange between CFD and WTM must not penalize overall simulation performance. A coupling strategy for data exchange is described and has been tested. It enables the parallel simulation of wind farms with WTM. Simulations of wind turbine wakes have been achieved. Preliminary results show the parallelization works properly but that the simulations do not resolve flows with enough accuracy.

  • High performance computing of the flow past a circular cylinder at critical and supercritical Reynolds numbers

     Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Borrell, Ricard; Paniagua Sánchez, Leslye; Perez Segarra, Carlos David
    International Conference on Parallel Computational Fluid Dynamics
    p. 166-172
    DOI: 10.1016/j.proeng.2013.07.110
    Presentation's date: 2013-05-22
    Presentation of work at congresses

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    It is well known that the flow past a circular cylinder at critical Reynolds number combines flow separation, turbulence transition, reattachment of the flow and further turbulent separation of the boundary layer. In the critical regime, the transition to turbulence in the boundary layer causes the delaying of the separation point and, an important reduction of the drag force on the cylinder surface known as the Drag Crisis. In this paper advanced turbulence simulations at Reynolds numbers in the range of 1.4 × 105-8.5 × 105 will be carried out by means of large-eddy simulations. Numerical simulations using unstructured grids up to 70 million of control volumes have been performed on Marenostrum Supercomputer. One of the major outcomes is shedding some light on the shear layer instabilities mechanisms and their role on the drag crisis phenomena.

  • Direct numerical simulation of viscoplastic-type non-Newtonian fluid flows in stenosed arteries

     Carmona Muñoz, Angel; Lehmkuhl Barba, Oriol; Perez Segarra, Carlos David; Oliva Llena, Asensio
    European Turbulence Conference
    Presentation's date: 2013-09-01
    Presentation of work at congresses

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    The aim of this work is to provide DNS solutions for turbulence flows of viscoplastic-type non-Newtonian fluids and thus contribute to gain insight into the underlying physics of the non-Newtonian turbulent flows. This knowledge may be useful, among many other things, for developing more accurate turbulence models which describe better the implicit physics of this subject. Nevertheless, from our point of view, few DNS solutions of viscoplastic-type non-Newtonian fluid flows have been provided with this objective, despite the growing presence of these kind of fluids in the field of CFD simulations.

  • Transient and dynamic numerical simulation of the fluid flow through valves based on large eddy simulation models

     Estruch Perez, Olga; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; Oliva Llena, Asensio; Perez Segarra, Carlos David
    International Conference on Compressors and Their Systems
    p. 577-587
    Presentation's date: 2013-09-09
    Presentation of work at congresses

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    The present paper attempts the dynamic simulation of the fluid flow through valve reed using the in-house implemented CFD and moving mesh coupled code TermoFluids. The CFD solver is based on a parallel, second-order, conservative and unstructured finite volume discretization. Large eddy simulation is performed to solve the turbulent flow, using the subgrid scale WALE model. The moving mesh technique uses RBF interpolation. As a preliminary approach, a simplified geometry of an axial hole plus a radial diffuser with a piston based inlet condition is considered. The valve dynamics is modelled by a specific law according modal analysis of valve reed. © The author(s) and/or their employer(s), 2013.

  • A new thermocline-PCM thermal storage concept for CSP plants. Numerical analysis and perspectives

     Galione Klot, Pedro Andres; Perez Segarra, Carlos David; Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim
    Solar Power and Chemical Energy Systems Conference
    Presentation's date: 2013-09
    Presentation of work at congresses

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    Thermocline storage concept has been considered for more than a decade as a possible solution to reduce the huge cost of the storage system in CSP plants. However, one of the drawbacks of this concept is the decrease in its performance throughout the time. The objective of this paper is to present a new thermocline-PCM storage concept which aims at circumventing this issue. The concept proposed is built of different solid filler materials and encapsulated PCMs combined into a multi-layer storage tank with molten salt as heat transfer fluid. The performance evaluation of each of the prototypes proposed is virtually tested by means of a detailed numerical methodology which considers the heat transfer and fluid dynamics phenomena present in these devices. The virtual tests carried out are designed so as to take into account several charging and discharging cycles until equilibrium is achieved, i.e. the same amount of energy stored in the charging phase is delivered in the discharge. As a result, the dependence of the storage capacity on the PCMs temperatures, the total energy stored/released, as well as the efficiencies of the storing process have been compared for the different thermocline, PCM-only and multi-layered thermocline-PCM configurations. Based on this analysis the selection of the best option for a given case/plant is proposed.

  • ISP-1 Deliverable 5.2.3 Modelling optimization

     Castro Gonzalez, Jesus; Perez Segarra, Carlos David; Rigola Serrano, Joaquim; Morales Ruiz, Sergio; Torras Ortiz, Santiago; Rodriguez Pérez, Ivette Maria; Oliva Llena, Asensio
    Date: 2012
    Report

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  • Assessment of the symmetry-preserving regularization model on complex flows using unstructured grids

     Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Rodriguez Pérez, Ivette Maria; Perez Segarra, Carlos David; Oliva Llena, Asensio
    Computers and fluids
    Vol. 60, p. 108-116
    DOI: 10.1016/j.compfluid.2012.02.030
    Date of publication: 2012-05-15
    Journal article

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    The main objective of the present paper is the assessment of symmetry-preserving regularization models on unstructured meshes. Three different test cases have been studied: the impinging jet flow, the flow past a circular cylinder and a simplified Ahmed car. The properties of the filters and their performance on general unstructured meshes have also been considered. A detailed analysis considering the Gaussian and the Helmholtz differential filters is presented.

  • A parallel radial basis function interpolation method for unstructured dynamic meshes

     Estruch Perez, Olga; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Perez Segarra, Carlos David; Oliva Llena, Asensio
    Computers and fluids
    p. 1-11
    DOI: 10.1016/j.compfluid.2012.06.015
    Date of publication: 2012-06-22
    Journal article

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  • Numerical simulation of turbulence at lower cost: regularization modeling

     Trias Miquel, Francesc Xavier; Gorobets, Andrey; Perez Segarra, Carlos David; Oliva Llena, Asensio
    Computers and fluids
    DOI: 10.1016/j.compfluid.2012.03.002
    Date of publication: 2012-03-13
    Journal article

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  • Numerical resolution of turbulent flows on complex geometries.  Open access

     Lehmkuhl Barba, Oriol
    Department of Heat Engines, Universitat Politècnica de Catalunya
    Theses

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    This thesis aims at developing a numerical methodology suitable for the direct numerical simulation (DNS) and large-eddy simulation (LES) of turbulent flows in order to be used in complex flows, currently encountered in industrial application. At the same time, the study of such turbulent flows can be an opportunity for gaining insight into the complex physics associated with them. To accomplish these goals, the mathematical formulation, conservative spatial discretization on unstructured grids and time- integration scheme for solving the Navier-Stokes equations are presented. The spatial discretization proposed preserves the symmetry properties of the continuous differential operator and ensure both, stability and conservation of the global kinetic energy balance on any grid. Furthermore, the time-integration technique proposed is an efficient self-adaptive strategy, based on a one-parameter second-order-explicit scheme, which has been successfully tested on both Cartesian staggered and unstructured collocated codes, leading to CPU cost reductions of up to 2.9 and 4.3, respectively. After presenting the general methodology for computing flows in complex geometries with unstructured grids, different LES models and regularization models suitable for these kind of meshes are presented and assessed by means of the analysis of different flows. First, regularization models are tested by means of the simulation of different cases with different level of complexity of the mesh. From a structured grid to a very complex mesh, with zones composed of prism and tetrahedral control volumes. It has been shown, that regularization models are very dependent on the quality of the filtering process. Although good results can be obtained with structured or smooth unstructuredmeshes, their performance is affected under fully irregular unstructured grids. A possible remedy to circumvent this issue is also presented. The main idea is to formulate the C4 model within a LES template. Although preliminary results are promising, further testing is still required. After regularization model assessment, LES models are also tested in a natural convection flow. It is shown that, although first order statistics are well solved for most of the models tested (with the exception of the Smagorinsky model), QR- and dynamic-Smagorinsky models present a better prediction of the second-order statistics. However, if CPU time is considered, then QR model is the best alternative. The second part of the thesis is devoted to the study of turbulent flows past bluff bodies. The cases studied are: the flow past a sphere, the flow past a circular cylinder and the flow past a NACA 0012 airfoil. All these cases shares some characteristics encountered in turbulent flows with massive separations, i.e., flow separation, transition to turbulence in the separated shear-layers and turbulent wakes with periodic shedding of vortices. However there are intrinsic characteristics of the turbulence in each of them, which make them interesting for the studying of the turbulence. Furthermore, the results presented for the flow past a sphere at Re = 3700 and 10000, together with the flow past a NACA 0012 at Re=50000 and AoA = 8 are the first DNS results presented in the literature for both flows. Conclusions drawn from the good results obtained point out that the use of the conservative formulation presented in this thesis, is one of the keys for the success of the SGS models used. This formulation, together with the use of unstructured grids might be a step towards the use of LES models for solving industrial flows on complex geometries at high Reynolds numbers.

    La present tesi proposa una metodologia apte per a realitzar simulacions directes de la turbulència (DNS) i simulacions de les grans escales (LES) de fluxos turbulents en geometries complexes. Tanmateix també s'estudia detalladament els mecanismes bàsics de funcionament dels fluxos turbulents en diferents situacions d'interès industrial i acadèmic. Per acomplir aquest objectiu s'ha desenvolupat una innovadora formulació matemàtica que permet conservar discretament les propietats continues de les equacions governants en malles no estructurades. La formulació proposada preserva la simetries originals dels operadors diferencials, assegurant així l'estabilitat i la conservació de l'energia cinètica turbulent en qualsevol mallat. Posteriorment s'ha proposat una metodologia d'integració temporal basada en una formulació explicita de segon ordre. Aquesta nova tècnica ha demostrat ser entre 2.9 i 4.3 més rapida que les tècniques anteriorment utilitzades per la comunitat. Un cop presentada la formulació per a simular fluxos turbulents en geometries complexes, s'han validat diferents models LES adaptats a malles no estructurades. Els models s'han testejat usant diferents solucions de referencia de la literatura i simulacions d'alt nivell generades en el context de la present tesi. Finalment s'ha conclòs que la conjunció de la formulació bàsica proposada amb alguns del models LES sorgits en els darrers anys es molt efectiva per a simular fluxos turbulents en situacions complexes, essent el Variational Multiscale WALE i el model QR els més adequats per a simular situacions de interes industrial. La segona part de la tesi es dedicada a l'estudi aerodinàmic del flux turbulent al voltant de diferents perfils. El perfils seleccionats son: el flux al voltant d'una esfera, flux al voltant d'un cilindre i flux al voltant d'un perfil NACA 0012. Els tres casos comparteixen fenomenologies com ara separació massiva de capes límits, esteles turbulentes i desprendiment periòdic de remolins. Tot i així cadascun d'ells es comporta diferent a nivell turbulent així que es d'interès estudiar-los i entendre quins son les causes de les diferencies físiques que es troben. Cal recordar que la física estudiada es la que es pot trobar posteriorment en ales d'avió, perfils de turbines de vent, aerodinàmica de cotxes, etc. Finalment recalcar que els resultats DNS del flux al voltant de l'esfera a Re=3700 i Re=10000 conjuntament amb els DNS del flux al voltant del perfil NACA a Re=50000 i AoA =8 son els primers presentats en la literatura internacional en el seu àmbit. Finalment es pot concloure que la formulació conservativa presentada en la tesis juntament amb els diferents models LES d'última generació testejats en la tesis, han demostrat ser una eina eficaç tan per a resoldre fluxos turbulents d'interès acadèmic com per simular situacions d'interès industrial.

  • Numerical Analysis and Experimental Studies of Vapour Compression Refrigerating Systems. Special Emphasis on Different Cycle Configurations  Open access

     Sadurni Caballol, Alexandre
    Department of Heat Engines, Universitat Politècnica de Catalunya
    Theses

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    The aim of this work is to study the thermal behavior and fluid-dynamic systems, vapor compression refrigeration and its components (heat exchangers, expansion devices, compressors, connecting pipes, pumps and pressure vessels). Topics discussed throughout this thesis arise from the growing interest in refrigerants friendly environment as well as different types of cooling systems for vapor compression has motivated the research group of the CTTC (Centre for Heat Transfer Technology ) to carry out major research efforts as well as participate in several projects with national and European institutions. The information contained in this thesis represents a summary of work performed by the author in recent years but also includes many of the contributions made by other members of CTTC. This thesis has led to the publication of several articles in international conferences. The main achievement of this thesis was the development of a numerical tool based on several subroutines flexibility to study different cooling Systemas vapor compression. The entire digital infrastructure has been the result of attaching specific numerical resolutions of each element of the cycle with the overall resolution algorithm. The simulations have been oriented to the study of thermodynamic cycle as well as to study some relevant aspects of the elements. In addition to the numerical results has been carried out important experimental work in the CTTC facilities in order to validate numerical models. The author has been fully involved in the process of data acquisition and has collaborated in the development of the units. The thesis is structured into five chapters plus a final conclusions and future actions. The first chapter, the introduction puts the reader in regard to the problematic situation, the history of cooling and objectives. The second presents the mathematical formulation and numerical methodology used in the simulation of the different elements and all cooling systems. The third study presents the numerical code verification. The fourth focuses on the validation of models with experimental results. And finally the fifth presents a suite of parametric studies and analysis. The numerical simulation code implemented has proven to be a flexible tool as various aspects of the steam compression systems have been successfully simulated and studied. It has also proven a reliable and good level of accuracy as the numerical results have been simulated properly the various experimental data compared.

  • Numerical simulation of radiative heat transfer in turbulent flows

     Capdevila Paramio, Roser
    Department of Heat Engines, Universitat Politècnica de Catalunya
    Theses

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  • Sistema de almacenamiento de energía térmica combinando material sólido de calor sensible y material de cambio de fase

     Oliva Llena, Asensio; Perez Segarra, Carlos David; Rigola Serrano, Joaquim; Castro Gonzalez, Jesus; Oliet Casasayas, Carles; Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Trias Miquel, Francesc Xavier; Capdevila Paramio, Roser; Galione Klot, Pedro Andres
    Date of request: 2012-12-27
    Invention patent

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    Un sistema para el almacenamiento y recuperación de energía térmica empleando como medio al menos un material de cambio de fase (sólido-líquido) y un material sólido de calor sensible que se encargan de almacenar/recuperar el calor obtenido desde una fuente externa en forma de calor sensible y calor latente de cambio de fase. Dichos materiales están debidamente contenidos en un único tanque, en cuyo interior existen al menos dos zonas, cada una conteniendo un material diferente, y diferenciadas por el rango de temperaturas a las que son sometidas. La configuración más usada consiste en tres diferentes zonas configuradas al interior del tanque: zona caliente, en la parte superior del tanque, donde un material de cambio de fase encapsulado caracterizado por una temperatura de fusión alta está encerrado; zona fría, ubicada en la parte inferior, donde un material de cambio de fase con baja temperatura de fusión está colocado; y una zona media, que contiene un material sólido de calor sensible.

  • Low Mach Navier-Stokes equations on unstructured meshes

     Ventosa Molina, Jordi; Chiva Segura, Jorge; Lehmkuhl Barba, Oriol; Perez Segarra, Carlos David; Oliva Llena, Asensio
    Conference on Modelling Fluid Flow
    p. 979-986
    Presentation's date: 2012-09-04
    Presentation of work at congresses

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  • Large-eddy simulation of turbulent dynamic fluid-structure interaction

     Estruch Perez, Olga; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Perez Segarra, Carlos David
    International Symposium on Turbulence, Heat and Mass Transfer
    Presentation's date: 2012-09-24
    Presentation of work at congresses

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  • Flow and heat transfer in a wall-bounded pin matrix

     Paniagua Sánchez, Leslye; Oliet Casasayas, Carles; Lehmkuhl Barba, Oriol; Perez Segarra, Carlos David
    International Symposium on Turbulence, Heat and Mass Transfer
    Presentation's date: 2012-09-26
    Presentation of work at congresses

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  • A parallel radial basis function interpolation method for unstructured dynamic meshes

     Estruch Perez, Olga; Borrell Pol, Ricard; Lehmkuhl Barba, Oriol; Perez Segarra, Carlos David
    International Conference on Parallel Computational Fluid Dynamics
    p. 1-2
    Presentation's date: 2012-05-25
    Presentation of work at congresses

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  • Access to the full text
    Detailed numerical model for the resolution of molten salt storage tanks for CSP plants  Open access

     Perez Segarra, Carlos David; Rodriguez Pérez, Ivette Maria; Torras Ortiz, Santiago; Oliva Llena, Asensio; Lehmkuhl Barba, Oriol
    ISES Europe Solar Conference
    p. 1-8
    Presentation's date: 2012-09-12
    Presentation of work at congresses

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    Considering the state-of-the-art in TES technologies, two-tank indirect system using molten salt is the most widespread within CSP plants. However, current techniques for design and optimization, as well as, for assessing the behaviour of these systems are mainly based on not-to-scale costly experimental set-ups. In this paper, a detailed numerical methodology modelling molten salt thermal storage tanks is presented. This methodology considers the transient behaviour of the molten-salt fluid, the gas ullage, the molten-salt free surface, the tank walls and insulation, different material in the foundation, radiation exchange between the salt and the tank walls in the ullage, the passive cooling in the foundation is proposed. Results for different configuration which allows an optimal design of the tank walls, insulation materials and tank foundations are presented.

  • Numerical modelling of the phase change material heat accumulator under fast transient gasification conditions in a low thrust cryogenic propulsion (LTCP) system

     Castro Gonzalez, Jesus; Galione Klot, Pedro Andres; Morales Ruiz, Juan José; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; Perez Segarra, Carlos David; Oliva Llena, Asensio
    International Conference on Space Propulsion
    Presentation's date: 2012-05-09
    Presentation of work at congresses

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  • Analysis of refrigerating cycles working with isobutane under transient conditions

     Ablanque Mejia, Nicolas; Rigola Serrano, Joaquim; Oliet Casasayas, Carles; Perez Segarra, Carlos David
    IIR-Gustav Lorentzen Conference on Natural Working Fluids
    p. 1 (928)-8 (935)
    Presentation's date: 2012-06-26
    Presentation of work at congresses

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  • Modular simulation of vapour compression systems with an object oriented tool

     Ablanque Mejia, Nicolas; Oliet Casasayas, Carles; Rigola Serrano, Joaquim; Lehmkuhl Barba, Oriol; Perez Segarra, Carlos David
    International Referigeration and Air Conditioning
    p. 2377, 1-2377, 8
    Presentation's date: 2012-07-16
    Presentation of work at congresses

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    The objective of this work is to simulate vapour compression refrigeration systems through a modular approach by means of an object - oriented numerical tool called NEST. For this purpose, the global system is modeled as a collection of different elements which are linked between them. Each element represents a specific part of the system (e.g. heat exchanger, compressor, expansion device, tube, cavity, wall, etc.) and can be independently solved for given boundary conditions. The global resolution procedure is carried out by solving all the elements iteratively, transferring information between them, until a converged solution is reached. The system is easily modified by adding, subtracting or substituting any of its elements. This feature gives great flexibility to the model, not only because the configuration of the system can be clearly altered, but also because the numerical model of any element can be easily replaced allowing different levels of simulation. In this work the object - oriented methodology together with the elements description and their resolution procedures are presented. The model is validated against experimental data obtained from a refrigeration cycle working with isobutane. In addition to this, an illustrative case is presented in order to show the system capabilities.

  • Use of a Low-Mach model on a CFD&HT solver for the elements of an object oriented program to numerically simulate hermetic refrigeration compressors

     Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; Lopez Mas, Joan; Perez Segarra, Carlos David
    International Compressor Engineering Conference
    p. 1385, 1-1385, 8
    Presentation's date: 2012-07-19
    Presentation of work at congresses

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    A powerful object oriented approach for the simulation of generic thermal systems (Damle et al., 2008) is used as a framework to numerically simulate the thermal and fluid behavior of hermetic reciprocating compressors. A physical abstraction of the compressor system provides a vertex-edge graph, defining the elements and the neighborhood relations of the system to be solved. Each one of these resulting elements is modeled in order to be solved by itself by giving their respective boundary conditions. Since each element provides its own solver tool, the coupled system can be solved in an integrated form. Into previous works, an unstructured and parallel object oriented Computational Fluid Dynamics and Heat Transfer code (from now on CFD&HT) for accurate and reliable solving of turbulent industrial flow, called TermoFluids (Lehmkuhl et al., 2007), was used to provide with CFD&HT capability the system elements (López et al., 2010). In this work, a Low-Mach based CFD&HT module (Chiva et al., 2011) implemented within the TermoFluids software has been used solve the fluid domain existing inside the shell of a reciprocating compressor, which is identified as one of the compressor elements in the abstraction stage. This improvement allows us to numerically simulate the recirculation flow inside the shell of a reciprocating compressor, providing detailed information about suction area of the compressor and allowing study of new geometric configurations of such part. Furthermore, in comparison with previously tested CFD&HT modules, the Low-Mach model allows better treatment of the compressibility effects generated at the inner elements of the compressor such as chambers, tubes and undoubtedly the compression chamber.

  • A filtered kinetic energy preserving finite volumes scheme for compressible flows

     Baez Vidal, Aleix; Lehmkuhl Barba, Oriol; Perez Segarra, Carlos David; Oliva Llena, Asensio
    Conference on Modelling Fluid Flow
    p. 987-994
    Presentation's date: 2012-09-04
    Presentation of work at congresses

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  • On LES assessment in massive separated flows: flow past a NACA airfoil at Re=50000

     Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Baez Vidal, Aleix; Perez Segarra, Carlos David
    European Mechanics Society Colloquium
    p. 31
    Presentation's date: 2012-02-23
    Presentation of work at congresses

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  • Numerical simulation of wrap scroll temperature for refrigeration and air conditioning compressors

     Rovira Casals, Jordi; Rigola Serrano, Joaquim; Perez Segarra, Carlos David; Oliva Llena, Asensio
    International Compressor Engineering Conference
    p. 1380, 1-1380, 8
    Presentation's date: 2012-07-16
    Presentation of work at congresses

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    Being part of a model which simulates the whole consecutive overall compression process in a scroll compressor by solving equations of mass, momentum and energy balance for fluid refrigerant (Rovira et al. ,2006), an updated version is presented. In this new model, an energy balance over the scroll wraps is implemented; where temperatures and heat fluxes are obtain ed dividing the wall into 36 parts (slices) each turn. The scroll wrap is divided into different solid slices; energy balance is carried out, taking into account: i) conduction along the scroll wrap; ii) convection heat transfer between each slice and each fluid chamber, with special attention on solid slice - fluid chamber contact at each time step. The numerical model shows the one dimensional and transient temperature, pressure and mass flow rate, at each fluid chamber along the scroll compressor, among detailed solid wrap temperature distribution. The whole numerical model has been experimentally validated against experimental data from technical literature (Halm,1997)(Chen et al.,2004a)(Chen et al.,2004b), comparing mass flow rate, discharge temperature, compression work and power consumption. Finally, the influence of wall temperatures and wall heat fluxes on the compressor performance and other output variables is analyzed.

  • Study of turbulent natural convection in a tall differentially heated cavity filled with either non-participating, participating grey and participating semigrey media

     Capdevila Paramio, Roser; Lehmkuhl Barba, Oriol; Colomer Rey, Guillem; Perez Segarra, Carlos David
    European Thermal Sciences Conference
    p. 1-9
    DOI: 10.1088/1742-6596/395/1/012155
    Presentation's date: 2012
    Presentation of work at congresses

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    Turbulent natural couvection in a tall differentially heated cavity of aspect ratio 5:1, filled with air under a Rayleigh number based on the height of 4.5.10(10), is studied numerically. Three different situations have been analysed. In the first one, the cavity is filled with a transparent medium. In the second one, the cavity is filled with a semigrey participating mixture, of air mid water vapour. In the List (me the cavity contains a grey participating gas. The turbulent flow is described by means of Large Eddy Simulation (LES) using symmetry-preserving discretizations. Simulations are compared with experimental data available in the literature and with Direct Numerical Simulations (DNS). Surface and gas radiation have been simulated using the Discrete Ordinates Method (DOM). The influence of radiation on fluid flow behaviour has been analysed.

  • Numerical solutions for the fluid flow and the heat transfer of viscoplastic-type non-Newtonian fluids

     Carmona Muñoz, Angel; Perez Segarra, Carlos David; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
    European Thermal Sciences Conference
    p. 1-9
    DOI: 10.1088/1742-6596/395/1/012002
    Presentation's date: 2012
    Presentation of work at congresses

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    The aim of this work is to provide numerical solutions for the fluid flow and the heat transfer generated in closed systems containing viscoplastic-type non-Newtonian fluids. A lid driven cavity (LDC) and a differentially heated cavity (DHC) are used as test cases. These numerical solutions can be an appropriate tool for verifying CFD codes which have been developed or adapted to deal with this kind of non-Newtonian fluids. In order to achieve this objective, an in-house CFD code has been implemented and correctly verified by the method of manufactured solutions and by some numerical solutions too. Furthermore, a high-performance CFD code (Termo Fluids S.L.) has been adapted and properly verified, by the corresponding numerical solutions, to deal with this kind of non-Newtonian fluids. The viscoplastic behaviour of certain non-Newtonian fluids will be generated from a viscous stress which has been defined by a potential-type rheological law. The pseudoplastic and dilatant behaviours will be studied. On this matter, the influence of different physical aspects on the numerical simulations will be analysed, e.g. different exponent values in the potential-type rheological law and different values of the non-dimensional numbers. Moreover, the influence of different numerical aspects on the numerical simulations will also be analysed, e.g. unstructured meshes, conservative numerical schemes and more efficient and parallel algorithms and solvers.

  • Numerical modeling of simultaneous heat and moisture transfer under complex geometry for refrigeration purposes

     Hou, Xiaofei; Rigola Serrano, Joaquim; Lehmkuhl Barba, Oriol; Oliet Casasayas, Carles; Perez Segarra, Carlos David
    European Thermal Sciences Conference
    p. 1-9
    DOI: 10.1088/1742-6596/395/1/012178
    Presentation's date: 2012
    Presentation of work at congresses

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    The aim of the paper is to gain a better insight into heat and moisture transfer in refrigerator and to do fundamental study for water evaporation and condensation in refrigeration application. The governing transport equations (continuity, momentum, energy and concentration equations) in 3D Cartesian coordinates are firstly introduced. As the mixed convection is simulated in the paper, buoyancy forces caused by both temperature and concentration gradient are considered and are also included in momentum equation. Numerical results are carried out by using Termofluids code. The pressure-velocity linkage is solved by means of an explicit finite volume fractional step procedure. In order to validate the code, a humid air flowing in a horizontal 3D rectangular duct case is carried out and compared with the published numerical and experimental results. The contour of temperature and vapor density of air at a cross section is provided and analyzed. Finally, the heat and mass transfer process during the moist air flow through complicated geometry is simulated and temperature and humidity distributions are obtained.

  • Towards the high performance computing of molten salt tanks for CSP plants

     Rodriguez Pérez, Ivette Maria; Perez Segarra, Carlos David; Estruch Perez, Olga; Oliva Llena, Asensio; Lehmkuhl Barba, Oriol
    Solar Power and Chemical Energy Systems Conference
    Presentation's date: 2012-09-12
    Presentation of work at congresses

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  • Numerical simulation of the turbulent fluid flow through valves based on low mach models

     Rigola Serrano, Joaquim; Lehmkuhl Barba, Oriol; Ventosa Molina, Jordi; Perez Segarra, Carlos David; Oliva Llena, Asensio
    International Compressor Engineering Conference
    p. 1375, 1-1375, 8
    Presentation's date: 2012-07-19
    Presentation of work at congresses

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    The aim of the present paper is to carry out a group of numerical experiments over the fluid flow through the valve reed, using the CFD&HT code TermoFluids, an unstructure d and parallel object-oriented CFD code for accurate and reliable solving of industrial flows (Lehmkuhl, O. et al. 2007 ) with special attention on incompressible hypothesis against low Mach compressible flow modeling, as a critic al numerical aspect depending on Reynolds number and gap thickness conditions. In all studied cases a multi-dimensional explicit finite volume fractional-step based algorithm extended to simulate low Mach fluxes using a Runge-Kutta/Crank-Nicholson time integration scheme, with a symmetry preserving discretization has been used. When turbulence modeling is needed, an extension of the WALE (Wall Adapting Local Eddy-viscosity) (Nicoud, F. and Ducros, F., 1999) model to non-structured meshes is applied. The pressure equation is solved by means of parallel Fourier Schur decomposition solver which is an efficient direct solver for loosely coupled PC clusters (Borrell, R. et al. 2011). In a two dimensional periodic way the fluid flow is approach ed by two parallel phenomena (an entrance flow through a channel and a free jet through a surface). In that sense, the present paper is focused on the numeri cal simulation model of the fluid flow through the valve reeds, considering a simplified geometry of an axial hole plus a radial diffuser. The numerical results presented are based on a specific geome try – valve diameter D is 3 times orifice diameter d, while s/d ratio is 0.6 – considering high Reynolds number at the entrance as boundary condition. The studied cases show the influence from laminar to turbulent flow from incompressible assumption to lower subsonic conditions and/or chocked flow.

  • Modular object-oriented methodology for the resolution of molten salt storage tanks for CSP plants

     Oliva Llena, Asensio; Perez Segarra, Carlos David; Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Torras, Santiago
    International Conference on Energy Storage
    Presentation's date: 2012-05-17
    Presentation of work at congresses

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  • Optimization of the thermal and fluid dynamic behaviour of air curtains: analysis of the plenum by means of LES

     Giraldez Garcia, Hector; Perez Segarra, Carlos David; Rodriguez Pérez, Ivette Maria; Oliva Llena, Asensio
    Conference on Modelling Fluid Flow
    p. 176-182
    Presentation's date: 2012-09-05
    Presentation of work at congresses

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  • DESARROLLO CODIGOS Y ALGORITMOS PARALELOS ALTA PRESTACIONES FINES DISEÑO OPTIMIZADO SISTEMAS Y EQUIPOS TERMICOS

     Perez Segarra, Carlos David; Trias Miquel, Francesc Xavier; Capdevila Paramio, Roser; Chiva Segura, Jorge; Gorobets, Andrey; Giraldez Garcia, Hector; Ventosa Molina, Jordi; Oliva Llena, Asensio
    Competitive project

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  • Numerical simulations of massive separated flows: flow over a stalled NACA airfoil

     Rodriguez Pérez, Ivette Maria; Oliva Llena, Asensio; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Baez Vidal, Aleix; Perez Segarra, Carlos David
    Competitive project

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