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    Wind speed effect on the flow field and heat transfer around a parabolic trough solar collector  Open access

     Amine Hachicha, Ahmed; Rodriguez Pérez, Ivette Maria; Oliva Llena, Asensio
    Applied energy
    Date of publication: 2014-10-01
    Journal article

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    Parabolic trough solar collectors are currently one of the most mature and prominent solar technology for the production of electricity. These systems are usually located in an open terrain where strong winds may be found, and could affect their stability and optical performance, as well as the heat exchange between the solar receiver and the ambient air. In this context, a wind flow analysis around a parabolic trough solar collector under real working conditions is performed. A numerical aerodynamic and heat transfer study based on Large Eddy Simulations is carried out to characterise the wind loads and heat transfer coefficients. After the study carried out by the authors in an earlier work (Hachicha et al. 2013) at ReW1=3.9e5, computations are performed at a higher Reynolds number of ReW2=1e6, and for various pitch angles. The effects of wind speed and pitch angle on the averaged and instantaneous flow are assessed. The aerodynamic coefficients are calculated around the solar collector and validated with measurements performed in wind tunnel tests. The variation of the heat transfer coefficient around the heat collector element with the Reynolds number is presented and compared to the circular cylinder in cross-flow. The unsteady flow is studied for three pitch angles: 0; 45 and 90 and different structures and recirculation regions are identified. A spectral analysis around the parabola and its receiver is also carried out in order to detect the most relevant frequencies related to the vortex shedding mechanism which affects the stability of the collector.

    Parabolic trough solar collectors are currently one of the most mature and prominent solar technology for the production of electricity. These systems are usually located in an open terrain where strong winds may be found, and could affect their stability and optical performance, as well as the heat exchange between the solar receiver and the ambient air. In this context, a wind flow analysis around a parabolic trough solar collector under real working conditions is performed. A numerical aerodynamic and heat transfer study based on Large Eddy Simulations is carried out to characterise the wind loads and heat transfer coefficients. After the study carried out by the authors in an earlier work (Hachicha et al. 2013) at ReW1=3.9e5, computations are performed at a higher Reynolds number of ReW2=1e6, and for various pitch angles. The effects of wind speed and pitch angle on the averaged and instantaneous flow are assessed. The aerodynamic coefficients are calculated around the solar collector and validated with measurements performed in wind tunnel tests. The variation of the heat transfer coefficient around the heat collector element with the Reynolds number is presented and compared to the circular cylinder in cross-flow. The unsteady flow is studied for three pitch angles: 0 ; 45 and 90 and different structures and recirculation regions are identified. A spectral analysis around the parabola and its receiver is also carried out in order to detect the most relevant frequencies related to the vortex shedding mechanism which affects the stability of the collector.

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    Limits of the Oberbeck¿Boussinesq approximation in a tall differentially heated cavity filled with water  Open access

     Kizildag, Deniz; Rodriguez Pérez, Ivette Maria; Oliva Llena, Asensio; Lehmkuhl Barba, Oriol
    International journal of heat and mass transfer
    Date of publication: 2014-01-01
    Journal article

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    The present work assesses the limits of the Oberbeck¿Boussinesq (OB) approximation for the resolution of turbulent fluid flow and heat transfer inside a tall differentially heated cavity of aspect ratio G = 6.67 filled with water (Pr = 3.27, Ra = 2.12e11). The cavity models the integrated solar collector-storage element installed on an advanced façade. The implications of the Oberbeck¿Boussinesq approximation is submitted to investigation by means of direct numerical simulations (DNS) carried out for a wide range of temperature differences. Non-Oberbeck¿Boussinesq (NOB) effects are found to be relevant, especially beyond the temperature difference of 30 °C, in the estimation of heat transfer, stratification, and flow configuration.

    The present work assesses the limits of the Oberbeck–Boussinesq (OB) approximation for the resolution of turbulent fluid flow and heat transfer inside a tall differentially heated cavity of aspect ratio G = 6.67 filled with water (Pr = 3.27, Ra = 2.12e11). The cavity models the integrated solar collector-storage element installed on an advanced façade. The implications of the Oberbeck–Boussinesq approximation is submitted to investigation by means of direct numerical simulations (DNS) carried out for a wide range of temperature differences. Non-Oberbeck–Boussinesq (NOB) effects are found to be relevant, especially beyond the temperature difference of 30 °C, in the estimation of heat transfer, stratification, and flow configuration.

  • Numerical simulation of wind flow around a parabolic trough solar collector

     Amine Hachicha, Ahmed; Rodriguez Pérez, Ivette Maria; Castro Gonzalez, Jesus; Oliva Llena, Asensio
    Applied energy
    Date of publication: 2013-07-01
    Journal article

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    The use of parabolic trough solar technology in solar power plants has been increased in recent years. Such devices are located in open terrain and can be the subject of strong winds. As a result, the stability of these devices to track accurately the sun and the convection heat transfer from the receiver tube could be affected. In this paper, a detailed numerical aerodynamic and heat transfer model based on Large Eddy Simulations (LES) modelling for these equipments is presented. First, the model is verified on a circular cylinder in a cross-flow. The drag forces and the heat transfer coefficients are then validated with available experimental measurements. After that, simulations are performed on an Eurotrough solar collector to study the fluid flow and heat transfer around the solar collector and its receiver. Computations are carried out for a Reynolds number of ReW = 3.6 × 105 (based on the aperture) and for various pitch angles (¿ = 0°, 45°, 90°, 135°, 180°, 270°). The aerodynamic coefficients are calculated around the solar collector and validated with measurements performed in wind tunnel tests. Instantaneous velocity field is also studied and compared to aerodynamic coefficients for different pitch angles. The time-averaged flow is characterised by the formation of several recirculation regions around the solar collector and the receiver tube depending on the pitch angle. The study also presents a comparative study of the heat transfer coefficients around the heat collector element with the circular cylinder in a cross-flow and the effect of the pitch angle on the Nusselt number.

    The use of parabolic trough solar technology in solar power plants has been increased in recent years. Such devices are located in open terrain and can be the subject of strong winds. As a result, the stability of these devices to track accurately the sun and the convection heat transfer from the receiver tube could be affected. In this paper, a detailed numerical aerodynamic and heat transfer model based on Large Eddy Simulations (LES) modelling for these equipments is presented. First, the model is verified on a circular cylinder in a cross-flow. The drag forces and the heat transfer coefficients are then validated with available experimental measurements. After that, simulations are performed on an Eurotrough solar collector to study the fluid flow and heat transfer around the solar collector and its receiver. Computations are carried out for a Reynolds number of Re W = 3.6 x 10(5) (based on the aperture) and for various pitch angles (h=0,45,90, 135, 80, 270). The aerodynamic coefficients are calculated around the solar collector and validated with measurements performed in wind tunnel tests. Instantaneous velocity field is also studied and compared to aerodynamic coefficients for different pitch angles. The time-averaged flow is characterised by the formation of several recirculation regions around the solar collector and the receiver tube depending on the pitch angle. The study also presents a comparative study of the heat transfer coefficients around the heat collector element with the circular cylinder in a cross-flow and the effect of the pitch angle on the Nusselt number.

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    Low-frequency unsteadiness in the vortex formation region of a circular cylinder  Open access

     Lehmkuhl Barba, Oriol; Rodriguez Pérez, Ivette Maria; Borrell Pol, Ricard; Oliva Llena, Asensio
    Physics of fluids
    Date of publication: 2013-08-23
    Journal article

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    The presence of low-frequency fluctuations in the wake of bluff bodies have been observed in several investigations. Even though the flow past a circular cylinder at Re = 3900 (Re = UrefD/¿) has been the object of several experimental and numerical investigations, there is a large scattering in the average statistics in the near wake. In the present work, the flow dynamics of the near wake region behind a circular cylinder has been investigated by means of direct numerical simulations and statistics have been computed for more than 858 shedding cycles. The analysis of instantaneous velocity signals of several probes located in the vortex formation region, point out the existence of a low-frequency fluctuation at the non-dimensional frequency of fm = 0.0064. This large-scale almost periodic motion seems to be related with the modulation of the recirculation bubble which causes its shrinking and enlargement over the time. Two different configurations have been identified: (i) a high-energy mode with larger fluctuations in the shear-layer and in the vortex formation region (Mode H) and (ii) a low-energy mode with weaker fluctuations in the shear layer (Mode L). The influence of such a low-frequency in the wake topology has been studied not only by means of the phase-average flow field for each mode, but also by the analysis of the time-average first- and second-order statistics of each wake mode. The results are compared with the long-term averaged solution and with results in the existing literature.

    The presence of low-frequency fluctuations in the wake of bluff bodies have been observed in several investigations. Even though the flow past a circular cylinder at Re = 3900 (Re = U ref D/ν) has been the object of several experimental and numerical investigations, there is a large scattering in the average statistics in the near wake. In the present work, the flow dynamics of the near wake region behind a circular cylinder has been investigated by means of direct numerical simulations and statistics have been computed for more than 858 shedding cycles. The analysis of instantaneous velocity signals of several probes located in the vortex formation region, point out the existence of a low-frequency fluctuation at the non-dimensional frequency of f m = 0.0064. This large-scale almost periodic motion seems to be related with the modulation of the recirculation bubble which causes its shrinking and enlargement over the time. Two different configurations have been identified: (i) a high-energy mode with larger fluctuations in the shear-layer and in the vortex formation region (Mode H) and (ii) a low-energy mode with weaker fluctuations in the shear layer (Mode L). The influence of such a low-frequency in the wake topology has been studied not only by means of the phase-average flow field for each mode, but also by the analysis of the time-average first- and second-order statistics of each wake mode. The results are compared with the long-term averaged solution and with results in the existing literature.

    Electronic version of an article published as "Physics of fluids", vol. 25, no 8, 2013. DOI: http://dx.doi.org/10.1063/1.4818641.

  • 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
    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.

    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.

  • Parallel algorithms for Sn transport sweeps on unstructured meshes

     Colomer Rey, Guillem; Borrell Pol, Ricard; Trias Miquel, Francesc Xavier; Rodriguez Pérez, Ivette Maria
    Journal of computational physics
    Date of publication: 2013-01-01
    Journal article

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    The Boltzmann Transport Equation is solved on unstructured meshes using the Discrete Ordinates Method. The flux for each ordinate is swept across the computational grid, within a source iteration loop that accounts for the coupling between the different ordinates. In this paper, a spatial domain decomposition strategy is used to divide the work among the available CPUs. The sequential nature of the sweep process makes the parallelization of the overall algorithm the most challenging aspect. Several parallel sweep algorithms, which represent different options of interleaving communications and calculations in the solution process, are analysed. The option of grouping messages by means of buffering is also considered. One of the heuristics proposed consistently stands out as the best option in all the situations analyzed, which include different geometries and different sizes of the ordinate set. With this algorithm, good scalability results have been achieved regarding both weak and strong speedup tests with up to 2560 CPUs.

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    Direct numerical simulation of a NACA0012 in full stall  Open access

     Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio; Borrell Pol, Ricard
    International journal of heat and fluid flow
    Date of publication: 2013-10-15
    Journal article

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    This work aims at investigating the mechanisms of separation and the transition to turbulence in the separated shear-layer of aerodynamic profiles, while at the same time to gain insight into coherent structures formed in the separated zone at low-to-moderate Reynolds numbers. To do this, direct numerical simulations of the flow past a NACA0012 airfoil at Reynolds numbers Re = 50,000 (based on the free-stream velocity and the airfoil chord) and angles of attack AOA = 9.25 and AOA = 12 have been carried out. At low-to-moderate Reynolds numbers, NACA0012 exhibits a combination of leading-edge/trailing-edge stall which causes the massive separation of the flow on the suction side of the airfoil. The initially laminar shear layer undergoes transition to turbulence and vortices formed are shed forming a von Kármán like vortex street in the airfoil wake. The main characteristics of this flow together with its main features, including power spectra of a set of selected monitoring probes at different positions on the suction side and in the wake of the airfoil are provided and discussed in detail.

    This work aims at investigating the mechanisms of separation and the transition to turbulence in the separated shear-layer of aerodynamic profiles, while at the same time to gain insight into coherent structures formed in the separated zone at low-to-moderate Reynolds numbers. To do this, direct numerical simulations of the flow past a NACA0012 airfoil at Reynolds numbers Re = 50,000 (based on the free-stream velocity and the airfoil chord) and angles of attack AOA = 9.25 and AOA = 12 have been carried out. At low-to-moderate Reynolds numbers, NACA0012 exhibits a combination of leading-edge/trailing-edge stall which causes the massive separation of the flow on the suction side of the airfoil. The initially laminar shear layer undergoes transition to turbulence and vortices formed are shed forming a von Kármán like vortex street in the airfoil wake. The main characteristics of this flow together with its main features, including power spectra of a set of selected monitoring probes at different positions on the suction side and in the wake of the airfoil are provided and discussed in detail.

  • Parallel sweep-based preconditioner for the solution of the linear Boltzmann transport equation

     Borrell Pol, Ricard; Colomer Rey, Guillem; Lehmkuhl Barba, Oriol; Rodriguez Pérez, Ivette Maria; Oliva Llena, Asensio
    Computers and fluids
    Date of publication: 2013-12-15
    Journal article

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    The Boltzmann transport equation is solved in the context of radiative heat transfer, for an isotropically scattering medium with reflecting boundaries. Under these circumstances, the different ordinates of the angular flux are mutually coupled. We explore here the use of a parallel sweep-based block diagonal preconditioner as a complement of the GMRES solver on the solution of the discretization matrix (which includes all the inter-ordinate couplings). The validity of this approach, when compared to the standard source iteration scheme, is successfully assessed for a significant range of the coupling parameters.

  • 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
    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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    Heat transfer analysis and numerical simulation of a parabolic trough solar collector  Open access

     Amine Hachicha, Ahmed; Rodriguez Pérez, Ivette Maria; Capdevila Paramio, Roser; Oliva Llena, Asensio
    Applied energy
    Date of publication: 2013-11-01
    Journal article

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    Parabolic trough solar collector is the most proven industry-scale solar generation technology today available. The thermal performance of such devices is of major interest for optimising the solar field output and increase the efficiency of power plants. In this paper, a detailed numerical heat transfer model based on the finite volume method for these equipment is presented. In the model, the different elements of the receiver are discretised into several segments in both axial and azimuthal directions and energy balances are applied for each control volume. An optical model is also developed for calculating the non-uniform solar flux distribution around the receiver. This model is based on finite volume method and ray trace techniques and takes into account the finite size of the Sun. The solar heat flux is determined as a pre-processing task and coupled to the energy balance model as a boundary condition for the outer surface of the receiver. The set of algebraic equations are solved simultaneously using direct solvers. The model is thoroughly validated with results from the literature. First, the optical model is compared with known analytical solutions. After that, the performance of the overall model is tested against experimental measurements from Sandia National Laboratories and other un-irradiated receivers experiments. In all cases, results obtained shown a good agreement with experimental and analytical results.

    Parabolic trough solar collector is the most proven industry-scale solar generation technology today available. The thermal performance of such devices is of major interest for optimising the solar field output and increase the efficiency of power plants. In this paper, a detailed numerical heat transfer model based on the finite volume method for these equipment is presented. In the model, the different elements of the receiver are discretised into several segments in both axial and azimuthal directions and energy balances are applied for each control volume. An optical model is also developed for calculating the non-uniform solar flux distribution around the receiver. This model is based on finite volume method and ray trace techniques and takes into account the finite size of the Sun. The solar heat flux is determined as a pre-processing task and coupled to the energy balance model as a boundary condition for the outer surface of the receiver. The set of algebraic equations are solved simultaneously using direct solvers. The model is thoroughly validated with results from the literature. First, the optical model is compared with known analytical solutions. After that, the performance of the overall model is tested against experimental measurements from Sandia National Laboratories and other un-irradiated receivers experiments. In all cases, results obtained shown a good agreement with experimental and analytical results.

  • Flow dynamics in the turbulent wake of a sphere at sub-critical Reynolds numbers

     Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Oliva Llena, Asensio
    Computers and fluids
    Date of publication: 2013-07-10
    Journal article

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    Direct numerical simulations of the flow over a sphere have been performed. The computations have been carried out in the sub-critical regime at Re = 3700 and Re = 10,000 (based on the free-stream velocity and the sphere diameter). A parallel unstructured symmetry-preserving formulation has been used for simulating the flow. Computations have been carried out on unstructured grids obtained by the constant-step rotation about the axis of a two-dimensional grid. With this discretisation, the Poisson equation has been solved by means of a Fourier diagonalization method. Particular attention has been devoted to investigate the shear-layer instabilities and its influence in the vortical structures, as well as the wake configuration. The main features of the flow including power spectra of a set of selected monitoring probes at different positions have been described and discussed in detail. Detailed information about turbulent statistics have also been provided.

  • Numerical modelling of a parabolic trough solar collector  Open access

     Amine Hachicha, Ahmed
    Defense's date: 2013-09-30
    Universitat Politècnica de Catalunya
    Theses

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    Las tecnologías de energía solar concentrada (CSP) están ganando cada vez más interés en la generación de electricidad debido al buen potencial para el escalemento las energías renovables a nivel de utilidad. El colector solar cillindro-parabólico (PTC) es el más económico, probado y avanzado de las diferentes tecnologías CSP. El modelado de estos dispositivos es una parte fundamental en la mejora de su diseño y rendemiento que puede representar un considerable aumento de la eficiencia global de las plantas de energía solar. En el tema demodelado y mejora del rendimiento de los PTC y sus absorbente (HCE), el estudio térmico, óptico y aerodinámico del flujo de fluidos y transferencia de calor es una herramienta importante para la optimización de la producción del parque solar y el incremento del rendimiento de la planta solar . Esta tesis se centra en la implementación de una metodología general para simular el comportamiento térmico, óptico y aerodinámico de PTCs . Se plantea una metodología para el modelado térmico de un PTC, teniendo en cuenta el flujo de calor real no uniforme en la direccion azimutal. Aunque ab initio, se consideró el método de volúmenes finitos ( FVM ) para la solución de la ecuación de transferencia radiativa , este ha sido posteriormente descartado entre otras razones debido al alto coste computacional y la incapacidad del método para tratar el tamaño angular del Sol. Para superar estos asuntos , se ha desarollado un nuevo modelo óptico. El nuevo modelo que esta basdo tanto las técnicas de FVM y de ray tracing, utiliza un enfoque numérico - geométrico para considerar el cono óptico. Se aborda el effecto de differentes factores, tales como ángulo de incidencia , la concentración geométrica y el ángulo de borde en la distribución del flujo de calor solar. La precisión del nuevo modelo se ha verificado y se ha obentido mejores resultados que el Monte Carlo Ray Tracing MCRT. Por otra parte, se ha analizado el comportamiento térmico del PTC teniendo en cuenta la distribución no uniforme de flujo solar en la direccion azimutal. Se ha desarrollado un modelo de rendimiento general basado en un balance energético sobre el HCE. Las pérdidas de calor y el rendimiento térmico se han determinado y validado con respecto a los experimentos de laboratorios de Sandia. Se muestro tambien la similitud entre el perfil de temperatura del absorbedor y del vidrio con la distribución de flujo solar. Además , se ha considerado las pérdidas de calor por convección hacia la atmósfera y el efecto del flujo de viento en la fuerza aerodinámica que actúa sobre la structura del PTC. Para ello se llevan a cabo, simulaciones numéricas detalladas basadas en Large Eddy Simulations (LES) para dos números de Reynolds de Re_W1= 3,6 10^5 y RE_ W2=1 .10^6. Estos numéros corresponden a condiciones similares de trabajo que aquellos encuentrado en las plantas solares de Eurotrough PTC. El estudio ha considerado diferentes ángulos de paso imitantdo las condiciones reales del mecanismo de seguimiento de PTC a lo largo del día . Las cargas aerodinámicas, es decir, los coeficientes de arrastre y elevación, han sido calculados y validados respecto a los mediciones realizadas en túneles de viento . Se muestra la independencia de los coeficientes aerodinámicos respecto a los números de Reynolds en los rangos estudiado. En cuanto a la transferencia de calor por convección alrededor del absorbedor, se han calculado los promediados del número de Nusselt local para los diferentes ángulos de paso y números de Reynolds y se ha analizado el efecto de la parábola en las pérdidas de calor. Por último, pero no menos importante, el análisis detallado de las furezas transitorias que actúan sobre la estructura de PTC han sido conducidas mediante espectro de potencia en varias sondas . El análisis ha detectado un aumento de la inestabilidad al mover el PTC para angulos de paso intermedios.

    Concentrated Solar Power (CSP) technologies are gaining increasing interest in electricity generation due to the good potential for scaling up renewable energy at the utility level. Parabolic trough solar collector (PTC) is economically the most proven and advanced of the various CSP technologies. The modelling of these devices is a key aspect in the improvement of their design and performances which can represent a considerable increase of the overall efficiency of solar power plants. In the subject of modelling and improving the performances of PTCs and their heat collector elements (HCEs), the thermal, optical and aerodynamic study of the fluid flow and heat transfer is a powerful tool for optimising the solar field output and increase the solar plant performance. This thesis is focused on the implementation of a general methodology able to simulate the thermal, optical and aerodynamic behaviour of PTCs. The methodology followed for the thermal modelling of a PTC, taking into account the realistic non-uniform solar heat flux in the azimuthal direction is presented. Although ab initio, the finite volume method (FVM) for solving the radiative transfer equation was considered, it has been later discarded among other reasons due to its high computational cost and the unsuitability of the method for treating the finite angular size of the Sun. To overcome these issues, a new optical model has been proposed. The new model, which is based on both the FVMand ray tracing techniques, uses a numerical-geometrical approach for considering the optic cone. The effect of different factors, such as: incident angle, geometric concentration and rim angle, on the solar heat flux distribution is addressed. The accuracy of the new model is verified and better results than the Monte Carlo Ray Tracing (MCRT) model for the conditions under study are shown. Furthermore, the thermal behaviour of the PTC taking into account the nonuniform distribution of solar flux in the azimuthal direction is analysed. A general performance model based on an energy balance about the HCE is developed. Heat losses and thermal performances are determined and validated with Sandia Laboratories tests. The similarity between the temperature profile of both absorber and glass envelope and the solar flux distribution is also shown. In addition, the convection heat losses to the ambient and the effect of wind flow on the aerodynamic forces acting on the PTC structure are considered. To do this, detailed numerical simulations based on Large Eddy simulations (LES) are carried out. Simulations are performed at two Reynolds numbers of ReW1 = 3.6 × 105 and ReW2 = 1 × 106. These values corresponds to working conditions similar to those encountered in solar power plants for an Eurotrough PTC. The study has also considered different pitch angles mimicking the actual conditions of the PTC tracking mechanism along the day. Aerodynamic loads, i.e. drag and lift coefficients, are calculated and validatedwith measurements performed in wind tunnels. The indepen-dence of the aerodynamic coefficients with Reynolds numbers in the studied range is shown. Regarding the convection heat transfer taking place around the receiver, averaged local Nusselt number for the different pitch angles and Reynolds numbers have been computed and the influence of the parabola in the heat losses has been analysed. Last but not the least, the detailed analysis of the unsteady forces acting on the PTC structure has been conducted by means of the power spectra of several probes. The analysis has led to detect an increase of instabilities when moving the PTC to intermediate pitch angles. At these positions, the shear-layers formed at the sharp corners of the parabola interact shedding vortices with a high level of coherence. The coherent turbulence produces vibrations and stresses on the PTC structure which increase with the Reynolds number and eventually, might lead to structural failure under certain conditions.

  • DRAGON - Understanding the DRAG crisis: ON the flow past a circular cylinder from critical to trans-critical Reynolds numbers

     Oliva Llena, Asensio; Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Chiva Segura, Jorge
    Participation in a competitive project

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  • Vortex dynamics and coherent structures in swirling flows (Cont.)

     Oliva Llena, Asensio; Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Baez Vidal, Aleix
    Participation in a competitive project

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  • On the large-eddy simulations of the flow past a cylinder at critical Reynolds numbers

     Lehmkuhl Barba, Oriol; Rodriguez Pérez, Ivette Maria; Borrell Pol, Ricard; Chiva Segura, Jorge
    ERCOFTAC Workshop on Direct and Large-Eddy Simulation
    Presentation's date: 2013-04-03
    Presentation of work at congresses

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  • Flow past a NACA0012 airfoil: from laminar separation bubbles to fully stalled regime

     Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Oliva Llena, Asensio
    ERCOFTAC Workshop on Direct and Large-Eddy Simulation
    Presentation's date: 2013-04-04
    Presentation of work at congresses

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  • Direct and large-eddy simulation of non-oberbeck-boussinesq effects in a turbulent differentially heated cavity

     Kizildag, Deniz; Trias Miquel, Francesc Xavier; Rodriguez Pérez, Ivette Maria; Oliva Llena, Asensio
    ERCOFTAC Workshop on Direct and Large-Eddy Simulation
    Presentation's date: 2013-04-04
    Presentation of work at congresses

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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
    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.

    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.

  • Dynamic wall modelling for large-eddy simulation of wind turbine dedicated airfoils

     Calafell Sandiumenge, Joan; Lehmkuhl Barba, Oriol; Rodriguez Pérez, Ivette Maria; Oliva Llena, Asensio
    European Turbulence Conference
    Presentation's date: 2013-09
    Presentation of work at congresses

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    This work aims at modelling the flow behaviour past airfoils used for wind turbine blades at high Reynolds number and large angles of attack (AoA). A previous work has been carried out on the airfoil profiles of DU-93-W-210, DU-91-W2-250 and FX-77-W-500 with a parallel unstructured symmetry preserving formulation together with wall-adapting Local-eddy viscosity model within a variational multi-scale framework (VMS-WALE) as a subgrid-scale model. However for the FX-77-W-500 profile, a mismatch between experimental results and numerical ones has been observed for the drag coefficient. To overcome this disagreement, a dynamic wall model has been implemented in order to compute accurately the wall shear stress without increasing prohibitively the computational costs.

  • 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.

  • 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
    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.

  • On the CFD&HT of the flow around a parabolic trough solar collector under real working conditions

     Amine Hachicha, Ahmed; Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
    Solar Power and Chemical Energy Systems Conference
    Presentation's date: 2013-09
    Presentation of work at congresses

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    Parabolic trough solar collector is currently one of the most mature and prominent solar applications for production of electricity. These systems are usually located in open terrain where strong winds may occur and affect their stability and optical performance, as well as, the heat exchange between the solar receiver and the ambient air. In this context, a wind flow analysis around a parabolic trough solar collector under real working conditions is performed. A numerical aerodynamic and heat transfer study based on Large Eddy Simulations is carried out to characterize the wind loads and the heat transfer coefficients. Computations are performed for two Reynolds number ReW1=3.9×10^5 and ReW2=1×10^6 and various pitch angles. The effects of wind speed and pitch angle on the averaged and instantaneous flow have been assessed. The aerodynamic coefficients are calculated around the solar collectorand validated with measurements performed in wind tunnel tests. The variation of the heat transfer coefficient around the heat collector element with the Reynolds number is presented and compared to the circular cylinder in cross flow.

  • 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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  • On the validity of the Oberbeck-Boussinesq approximation in a tall differentially heated cavity with water

     Kizildag, Deniz; Rodriguez Pérez, Ivette Maria; Castro Gonzalez, Jesus
    Progress in computational fluid dynamics
    Date of publication: 2012-07-26
    Journal article

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  • Numerical resolution of the liquid¿vapour two-phase flow by means of the two-fluid model and a pressure based method

     Morales Ruiz, Sergio; Rigola Serrano, Joaquim; Rodriguez Pérez, Ivette Maria; Oliva Llena, Asensio
    International journal of multiphase flow
    Date of publication: 2012-07-01
    Journal article

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  • Modelling refrigerating compartment of frost-free domestic refrigerators

     Jaramillo Ibarra, Julian Ernesto; Rigola Serrano, Joaquim; Rodriguez Pérez, Ivette Maria; Oliet Casasayas, Carles
    Global NEST Journal
    Date of publication: 2012-06
    Journal article

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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
    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.

  • Parallel algorithms for Computational Fluid Dynamics on unstructured meshes  Open access

     Borrell Pol, Ricard
    Defense's date: 2012-10-31
    Department of Heat Engines, Universitat Politècnica de Catalunya
    Theses

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    La simulació numèrica directa (DNS) de fluxos complexes és actualment una utopia per la majoria d'aplicacions industrials ja que els requeriments computacionals son massa elevats. Donat un flux, la diferència entre els recursos computacionals necessaris i els disponibles és cobreix mitjançant la modelització/simplificació d'alguns termes de les equacions originals que regeixen el seu comportament. El creixement continuat dels recursos computacionals disponibles, principalment en forma de super-ordinadors, contribueix a reduir la part del flux que és necessari aproximar. De totes maneres, obtenir la eficiència esperada dels nous super-ordinadors no és una tasca senzilla i, per aquest motiu, part de la recerca en el camp de la Mecànica de Fluids Computacional es centra en aquest objectiu. En aquest sentit, algunes contribucions s'han presentat en el marc d'aquesta tesis. El primer objectiu va ser el desenvolupament d'un codi de CFD de propòsit general i paral·lel, basat en la metodologia de volums finits en malles no estructurades, per resoldre problemes de multi-física. Aquest codi, anomenat TermoFluids (TF), té un disseny orientat a objectes i pensat per ser usat de forma altament eficient en els super-ordinadors actuals. Amb el temps, ha esdevingut pel grup una eina fonamental en projectes tant de recerca bàsica com d'interès industrial. En el context d'aquesta tesis, el treball s'ha focalitzat en el desenvolupament de dos de les llibreries més bàsiques de TermoFluids: i) La Basics Objects Library (BOL), que es una plataforma de software sobre la qual estan programades la resta de llibreries del codi, i que conté els mètodes algebraics i geomètrics fonamentals per la implementació paral·lela dels algoritmes de discretització, ii) la Linear Solvers Library (LSL), que conté un gran nombre de mètodes per resoldre els sistemes d'equacions lineals derivats de les discretitzacions. El primer capítol d'aquesta tesi conté les principals idees subjacents al disseny i la implementació de la BOL i la LSL, juntament amb alguns exemples i algunes aplicacions industrials. En els capítols posteriors hi ha una explicació detallada de solvers específics per algunes aplicacions concretes. En el segon capítol, es presenta un solver paral·lel i directe per la resolució de l'equació de Poisson per casos en els quals una de les direccions del domini té condicions d'homogeneïtat. En la simulació de fluxos incompressibles, l'equació de Poisson es resol almenys una vegada en cada pas de temps, convertint-se en una de les parts més costoses i difícils de paral·lelitzar del codi. El mètode que proposem és una combinació d'una descomposició directa de Schur (DDS) i una diagonalització de Fourier. La darrera descompon el sistema original en un conjunt de sub-sistemes 2D independents que es resolen mitjançant l'algorisme DDS. Atès que no s'imposen restriccions a les direccions no periòdiques del domini, aquest mètode és aplicable a la resolució de problemes discretitzats mitjançat l'extrusió de malles 2D no estructurades. L'escalabilitat d'aquest mètode ha estat provada amb èxit amb un màxim de 8192 CPU per malles de fins a ~10⁹ volums de control. En el darrer capitol capítol, es presenta un mètode de resolució per l'equació de Transport de Boltzmann (BTE). La estratègia emprada es basa en el mètode d'Ordenades Discretes i pot ser aplicat en discretitzacions no estructurades. El flux per a cada ordenada angular es resol amb un mètode de substitució equivalent a la resolució d'un sistema lineal triangular. La naturalesa seqüencial d'aquest procés fa de la paral·lelització de l'algoritme el principal repte. Diversos algorismes de substitució han estat analitzats, esdevenint una de les heurístiques proposades la millor opció en totes les situacions analitzades, amb excel·lents resultats. Els testos d'eficiència paral·lela s'han realitzat usant fins a 2560 CPU.

    Direct Numerical Simulation (DNS) of complex flows is currently an utopia for most of industrial applications because computational requirements are too high. For a given flow, the gap between the required and the available computing resources is covered by modeling/simplifying of some terms of the original equations. On the other hand, the continuous growth of the computing power of modern supercomputers contributes to reduce this gap, reducing hence the unresolved physics that need to be attempted with approximated models. This growth, widely relies on parallel computing technologies. However, getting the expected performance from new complex computing systems is becoming more and more difficult, and therefore part of the CFD research is focused on this goal. Regarding to it, some contributions are presented in this thesis. The first objective was to contribute to the development of a general purpose multi-physics CFD code. referred to as TermoFluids (TF). TF is programmed following the object oriented paradigm and designed to run in modern parallel computing systems. It is also intensively involved in many different projects ranging from basic research to industry applications. Besides, one of the strengths of TF is its good parallel performance demonstrated in several supercomputers. In the context of this thesis, the work was focused on the development of two of the most basic libraries that compose TF: I) the Basic Objects Library (BOL), which is a parallel unstructured CFD application programming interface, on the top of which the rest of libraries that compose TF are written, ii) the Linear Solvers Library (LSL) containing many different algorithms to solve the linear systems arising from the discretization of the equations. The first chapter of this thesis contains the main ideas underlying the design and the implementation of the BOL and LSL libraries, together with some examples and some industrial applications. A detailed description of some application-specific linear solvers included in the LSL is carried out in the following chapters. In the second chapter, a parallel direct Poisson solver restricted to problems with one uniform periodic direction is presented. The Poisson equation is solved, at least, once per time-step when modeling incompressible flows, becoming one of the most time consuming and difficult to parallelize parts of the code. The solver here proposed is a combination of a direct Schur-complement based decomposition (DSD) and a Fourier diagonalization. The latter decomposes the original system into a set of mutually independent 2D sub-systems which are solved by means of the DSD algorithm. Since no restrictions are imposed in the non-periodic directions, the overall algorithm is well-suited for solving problems discretized on extruded 2D unstructured meshes. The scalability of the solver has been successfully tested using up to 8192 CPU cores for meshes with up to 10 9 grid points. In the last chapter, a solver for the Boltzmann Transport Equation (BTE) is presented. It can be used to solve radiation phenomena interacting with flows. The solver is based on the Discrete Ordinates Method and can be applied to unstructured discretizations. The flux for each angular ordinate is swept across the computational grid, within a source iteration loop that accounts for the coupling between the different ordinates. The sequential nature of the sweep process makes the parallelization of the overall algorithm the most challenging aspect. Several parallel sweep algorithms, which represent different options of interleaving communications and calculations, are analyzed. One of the heuristics proposed consistently stands out as the best option in all the situations analyzed. With this algorithm, good scalability results have been achieved regarding both weak and strong speedup tests with up to 2560 CPUs.

  • 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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  • Towards the understanding of shear-layer instability mechanisms for drag reduction by means of advanced turbulence modeling

     Oliva Llena, Asensio; Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Calafell Sandiumenge, Joan
    Participation in a competitive project

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  • Towards the understanding of shear-layer instability mechanisms for drag reduction by means of advanced turbulence modeling(Cont.)

     Oliva Llena, Asensio; Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Calafell Sandiumenge, Joan
    Participation in a competitive project

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  • Vortex dynamics and coherent structures in swirling flows

     Oliva Llena, Asensio; Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Baez Vidal, Aleix
    Participation in a competitive project

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  • Large-eddy simulations of wind turbine dedicated airfoils at high Reynolds numbers

     Lehmkuhl Barba, Oriol; Rodriguez Pérez, Ivette Maria; Calafell Sandiumenge, Joan; Oliva Llena, Asensio
    European Mechanics Society Colloquium
    Presentation's date: 2012-02-22
    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
    Presentation's date: 2012-02-23
    Presentation of work at congresses

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  • High-Performance computing of flows with massive separation: flow past a NACA 0012

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

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  • 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
    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.

  • Flow and turbulent structures around simplified car models

     Aljure Osorio, David E.; Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Oliva Llena, Asensio
    Conference on Modelling Fluid Flow
    Presentation's date: 2012-09-06
    Presentation of work at congresses

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  • Captador solar con aislamiento transparente plástico y protección al sobrecalentamiento

     Castro Gonzalez, Jesus; Oliva Llena, Asensio; Rodriguez Pérez, Ivette Maria
    Date of request: 2012-03-02
    Invention patent

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    Captador solar con aislamiento transparente plástico y protección al sobrecalentamiento.

    La presente invención tiene como finalidad perfeccionar la mejora de captadores solares térmicos planos o de baja concentración con aislamiento térmico transparente en la cubierta, aumentando su rendimiento, minimizando los costes de producción y el peso de éstos.

    Más concretamente, se refiere al uso de sistemas de protección al sobrecalentamiento de los materiales transparentes aislantes plásticos en estructura alveolar mediante canal de ventilación.

    También se plantea el concepto de captador integrado con cubierta con aislamiento transparente plástico en estructura alveolar, en el que existe un depósito de un fluido que actúa de acumulador de energía térmica, integrado en el captador, que a la vez dota de inercia térmica a todo el sistema, limitando la temperatura máxima alcanzada en el mismo. El depósito acumulador incorpora una válvula limitadora de presión y temperatura, aprovechando el calor latente de cambio de fase líquido/vapor.

  • 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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  • Solid-liquid phase change with turbulent flow

     Galione Klot, Pedro Andres; Rigola Serrano, Joaquim; Castro Gonzalez, Jesus; Rodriguez Pérez, Ivette Maria
    International Symposium on Turbulence, Heat and Mass Transfer
    Presentation's date: 2012-09-26
    Presentation of work at congresses

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    The present paper describes a numerical simulation of the solid-liquid phase change Computational Fluid Dynamics and Heat Transfer (CFD&HT) model developed in order to account for natural convection inside Phase Change Materials (PCMs) taking into account turbulent effects.

  • On the large-eddy simulation modelling of wind turbine dedicated airfoils at high Reynolds numbers

     Calafell Sandiumenge, Joan; Lehmkuhl Barba, Oriol; Rodriguez Pérez, Ivette Maria; Oliva Llena, Asensio
    International Symposium on Turbulence, Heat and Mass Transfer
    Presentation's date: 2012-09-27
    Presentation of work at congresses

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    Large-eddy simulations of fluid flow and heat transfer around a parabolic trough solar collector  Open access

     Amine Hachicha, Ahmed; Rodriguez Pérez, Ivette Maria; Oliva Llena, Asensio
    ISES Europe Solar Conference
    Presentation's date: 2012-09-12
    Presentation of work at congresses

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    This study reports on numerical simulations of a parabolic trough solar collector to predict the aerodynamic behaviour and the convection heat transfer from the heat collector element. In the study, the variation of fluid flow with different angles of attack has been taken into account. Calculations are performed using Large Eddy Simulations with a Variational Multiscale (VMS)approach for modelling the sub-grid scale stress tensor. The governing equations are discretised on a collocated unstructured grid arrangement by means of second-order spectro-consistent schemes. The numerical model is validated first with a cross flow around a horizontal cylinder. After that,aerodynamic coefficients at different angles of attack or pitch angles are calculated and compared to wind-tunnel experiments. It has been shown that, the orientation of the solar collector plays an important role in evaluating the aerodynamic performance and structural design criteria of the collector.

  • 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
    Presentation's date: 2012-09-05
    Presentation of work at congresses

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  • Low-frequency unsteadiness in the vortex formation region of a circular cylinder

     Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Oliva Llena, Asensio
    International Symposium on Turbulence, Heat and Mass Transfer
    Presentation's date: 2012-09-27
    Presentation of work at congresses

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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
    Presentation of work at congresses

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  • Direct numerical simulation of a NACA0012 in full stall

     Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Baez Vidal, Aleix; Borrell Pol, Ricard; Oliva Llena, Asensio
    Conference on Modelling Fluid Flow
    Presentation's date: 2012-09-06
    Presentation of work at congresses

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  • Coupling CFD models of airflow with building simulation with an object-oriented and parallel infrastructure

     Damle, Rashmin; Lehmkuhl Barba, Oriol; Rodriguez Pérez, Ivette Maria; Oliva Llena, Asensio
    ISES Europe Solar Conference
    Presentation's date: 2012-09-12
    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 simulations of energy storage with encapsulated phase change materials. Special emphasis on solid-liquid phase change CFD modelling

     Galione Klot, Pedro Andres; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; Oliva Llena, Asensio; Rodriguez Pérez, Ivette Maria
    International Conference on Energy Storage
    Presentation's date: 2012-05-17
    Presentation of work at congresses

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