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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
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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
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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.

  • 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
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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 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
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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.

  • 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
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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.

  • 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
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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.

  • 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
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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.

  • Experimental studies of fin-and-tube evaporators for household no-frost refrigerators

     Oliet Casasayas, Carles; Rigola Serrano, Joaquim; Perez Segarra, Carlos David; Sadurní, Alexandre
    World Conference on Experimental Heat Transfer, Fluid Mechanics, and Thermodynamics
    Presentation's date: 2013-06-17
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  • 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.

  • 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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  • 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
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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
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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.

  • 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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  • 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.

  • 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
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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
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  • 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
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    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
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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.

  • 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
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  • 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
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  • 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
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  • 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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  • 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 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
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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.

  • 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
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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.

  • 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.

  • 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.

  • 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 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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  • 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
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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
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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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  • 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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  • 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.

  • Turbulent natural convection in a differentially heated cavity of aspect ratio 5 filled with non-participating and participating grey media

     Capdevila Paramio, Roser; Lehmkuhl Barba, Oriol; Trias Miquel, Francesc Xavier; Perez Segarra, Carlos David; Colomer, G.
    European Turbulence Conference
    p. 1-10
    DOI: 10.1088/1742-6596/318/4/042048
    Presentation's date: 2011-12-22
    Presentation of work at congresses

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    In the present work, turbulent natural convection in a tall differentially heated cavity of aspect ratio 5:1, filled with air (Pr = 0.7) under a Rayleigh number based on the height of 4.5 centerdot 1010, is studied numerically. Two different situations have been analysed. In the first one, the cavity is filled with a transparent medium. In the second one, 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 also been analysed.

  • Numerical simulations of massive separated flows: flow over a stalled NACA airfoil (Cont.)

     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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  • Access to the full text
    Low-frequency variations in the wake of a circular cylinder at Re = 3900  Open access

     Lehmkuhl Barba, Oriol; Rodriguez Pérez, Ivette Maria; Borrell Pol, Ricard; Perez Segarra, Carlos David; Oliva Llena, Asensio
    European Turbulence Conference
    p. 1-6
    Presentation's date: 2011-09-13
    Presentation of work at congresses

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    Flow around cylindrical structures is of relevance for many practical applications. Knowledge of flow-related unsteady loading of such structures is crucial for hydro- and aerodynamic control and design. In order to obtain a deeper knowledge of this kind of flow, a DNS have been performed at ReD = 3900 (ReD = UrefD/v). The instantaneous velocity signals of probes located in the separated shear-layer and in the vortex formation region exhibit the presence of low-frequency variations. The statistical analysis of these signals suggest that low-frequency variations in the vortex formation length, suction base pressure and intermittencies in the shear layer are closely related. It is shown that these variations are the responsible of the large scattering of data obtained in different experimental and numerical results, as well as the U-shape and V-shape stream-wise velocity profiles observed in the very near wake of the cylinder.

  • Transient response in small capacity vapour compression systems. Experimental data and numerical approach

     Ablanque Mejia, Nicolas; Rigola Serrano, Joaquim; Oliet Casasayas, Carles; Perez Segarra, Carlos David
    IIR International Congress of Refrigeration
    p. 1-8
    Presentation's date: 2011-08-21
    Presentation of work at congresses

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    The aim of this work is to introduce a numerical approach to study the transient response of vapour compression refrigerating systems. The emphasis is put on small capacity systems working with R600a (power consumption lower than 1 kW). The proposed method consists in linking all the specific sub-models of the cycle main components (compressor, heat exchangers and expansion device) and transferring adequate information from one to each other until convergence is reached. The model allows to simulate both steadystate and transient conditions. In order to validate the numerical scheme, an experimental facility (specially designed to analyze domestic refrigerators) has been built and used to collect relevant measurements. The work is focused on a specific case considering domestic refrigerating conditions at both steady-state and transient conditions. The numerical steady-state conditions are compared against experimental data, while a detailed transient process is numerically studied.

  • Numerical analysis of no-frost domestic refrigerator evaporators

     Oliet Casasayas, Carles; Perez Segarra, Carlos David; Oliva Llena, Asensio; Rigola Serrano, Joaquim
    IIR International Congress of Refrigeration
    p. 1-8
    Presentation's date: 2011-08-21
    Presentation of work at congresses

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    The air-to-refrigerant evaporator placed in no-frost refrigerators is a critical component because of its simultaneous treatment of both cooler and freezer air streams, which implies a strong drying process on the cooler air flow, and the corresponding intense and non-uniform frost formation process. This paper presents a numerical model developed to analyse fin-and-tube heat exchangers in general and this kind of evaporators in particular. This is a distributed model which gives a very detailed picture of the nonuniform heat exchanger behaviour in terms of heat and mass transfer, considering local effects (frost formation, fin density, in-flow state, etc.). The mathematical formulation and the numerical methodology are presented, showing the model capabilities and level of analysis. Afterwards, illustrative computational results show the potential of the model as a design tool for this application. Validation studies are included in an accompanying paper.

  • Analysis of vapour-compression refrigerating systems

     Sadurni Caballol, Alexandre; Oliet Casasayas, Carles; Rigola Serrano, Joaquim; Perez Segarra, Carlos David
    IIR International Congress of Refrigeration
    p. 1-8
    Presentation's date: 2011-08-21
    Presentation of work at congresses

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    The aim of this paper is to show the authors proposal for steady state numerical simulation of Vapour-Compression Refrigerating Systems (dry expansion, liquid overfeed systems, ...). The developed tool allows using different levels of simulation for some elements (compressors, pipes, etc.) as well as the possibility of use different kind of expansion devices. A verification study for a steady state regime is presented analysing also influence of mesh density and of the numerical accuracy. A validation study for steady state regime is shown. Some computational results for steady state regime are also presented to provide an overview of the level of detail given by the model. A set of parametric studies is finally given to evaluate the influence of some boundary conditions (environmental temperature, secondary inlet temperatures, etc.).

  • Experimental analysis of no-frost domestic refrigerator evaporators

     Oliet Casasayas, Carles; Perez Segarra, Carlos David; Oliva Llena, Asensio; Rigola Serrano, Joaquim
    IIR International Congress of Refrigeration
    p. 1-8
    Presentation's date: 2011-08-21
    Presentation of work at congresses

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    The air-to-refrigerant evaporator placed in no-frost refrigerators is a critical component because of its simultaneous treatment of both cooler and freezer air streams, which implies a strong drying process on the cooler air flow, and the corresponding intense and non-uniform frost formation process. This paper presents a numerical model developed to analyse fin-and-tube heat exchangers in general and this kind of evaporators in particular. This is a distributed model which gives a very detailed picture of the nonuniform heat exchanger behaviour in terms of heat and mass transfer, considering local effects (frost formation, fin density, in-flow state, etc.). The mathematical formulation and the numerical methodology are presented, showing the model capabilities and level of analysis. Afterwards, illustrative computational results show the potential of the model as a design tool for this application. Validation studies are included in an accompanying paper.

  • 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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  • Modelization of the Low-Mach Navier Stokes equations in unstructured meshes

     Ventosa Molina, Jordi; Chiva Segura, Jorge; Lehmkuhl Barba, Oriol; Perez Segarra, Carlos David
    International Conference on Computational Heat and Mass Transfer
    p. 1-8
    Presentation's date: 2011-07-18
    Presentation of work at congresses

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    In this paper a Low-Mach number approximation of the Navier Stokes Equations in unstructured meshes is presented. Both staggered and collocated formulations for unstructured grids will be used.The aim is to develop a numerical algorithm suitable for describing flows which present large variations of the density field, but that the speed of the flow is low, so that the Mach number is small and if a compressible formulation was to be used would cause strong limitations to the time step. The test case for verification will be a differentially heated cavity with a large temperature gradient. The results will be compared against benchmark data.

  • Numerical resolution of the heat accumulator in a Low Cost Cryogenic Propulsion (LCCP) system

     Morales Ruiz, Sergio; Castro Gonzalez, Jesus; Rigola Serrano, Joaquim; Perez Segarra, Carlos David; Oliva Llena, Asensio
    European Conference for Aerospace Sciences
    p. 1-8
    Presentation's date: 2011-07-08
    Presentation of work at congresses

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  • Numerical simulations of turbulent natural convection coupled and uncoupled with radiation

     Capdevila Paramio, Roser; Lehmkuhl Barba, Oriol; Colomer Rey, Guillem; Trias Miquel, Francesc Xavier; Perez Segarra, Carlos David
    International Conference on Computational Heat and Mass Transfer
    p. 1-8
    Presentation's date: 2011-07-18
    Presentation of work at congresses

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    In the present work, turbulent natural convection in a tall differentially heated cavity of aspect ratio 5:1, filled with air (Pr = 0.7) under a Rayleigh number based on the height of 4.5 · 1010, is studied numerically. Two different situations have been analysed. In the first one, the cavity is filled with a transparent medium. In the second one, 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 also been analysed.