Articles de revista
http://hdl.handle.net/2117/3191
2015-12-01T05:44:31ZMulti-layered solid-PCM thermocline thermal storage for CSP. Numerical evaluation of its application in a 50 MWe plant
http://hdl.handle.net/2117/76396
Multi-layered solid-PCM thermocline thermal storage for CSP. Numerical evaluation of its application in a 50 MWe plant
Galione Klot, Pedro Andrés; Pérez Segarra, Carlos David; Rodríguez Pérez, Ivette María; Torras Ortiz, Santiago; Rigola Serrano, Joaquim
Thermocline storage concept is considered as a possible solution to reduce the cost of thermal storage in concentrated solar power (CSP) plants. Recently, a multi-layered solid-PCM (MLSPCM) concept—consisting of a thermocline-like tank combining layers of solid and phase change filler materials—has been proposed. This approach was observed to result in lower thermocline degradation throughout charge/discharge cycles, due to the thermal buffering effect of the PCM layers located at both ends of the tank. MLSPCM prototypes designed for a pilot scale plant were numerically tested and compared against other designs of single-tank thermocline systems, such as: solid-filled thermocline, tanks filled with a single encapsulated PCM and cascaded-PCM configurations. Results showed promising results of the MLSPCM configurations for their potential use in CSP plants.
In this work, the MLSPCM concept is used for designing a thermal energy storage (TES) system for a CSP plant with the dimensions and operating conditions of a parabolic trough plant of 50 MWe, similar to Andasol 1 (Granada, Spain). The performance evaluation of each of the proposed prototypes is virtually tested by means of a numerical methodology which considers the heat transfer and fluid dynamics phenomena present in these devices. Two sets of cases are considered, one with the objective of testing the TES systems individually, by defining specific operating conditions and taking the systems to a periodic steady state; and another, aiming to evaluate their performance after several days of operation in a CSP plant, in which the weather variability and the thermal behavior of the tank walls and foundation are simulated. Thermal performance parameters, such as total energy and exergy stored/released and the efficiency in the use of the storage capacity, are calculated and compared with those obtained by other thermocline-like configurations (single-solid and single-PCM), and with a reference 2-tank molten-salt system. Obtained results allow to continue considering the MLSPCM concept as an interesting alternative for thermal storage in CSP facilities.
2015-07-30T10:14:45ZGalione Klot, Pedro AndrésPérez Segarra, Carlos DavidRodríguez Pérez, Ivette MaríaTorras Ortiz, SantiagoRigola Serrano, JoaquimThermocline storage concept is considered as a possible solution to reduce the cost of thermal storage in concentrated solar power (CSP) plants. Recently, a multi-layered solid-PCM (MLSPCM) concept—consisting of a thermocline-like tank combining layers of solid and phase change filler materials—has been proposed. This approach was observed to result in lower thermocline degradation throughout charge/discharge cycles, due to the thermal buffering effect of the PCM layers located at both ends of the tank. MLSPCM prototypes designed for a pilot scale plant were numerically tested and compared against other designs of single-tank thermocline systems, such as: solid-filled thermocline, tanks filled with a single encapsulated PCM and cascaded-PCM configurations. Results showed promising results of the MLSPCM configurations for their potential use in CSP plants.
In this work, the MLSPCM concept is used for designing a thermal energy storage (TES) system for a CSP plant with the dimensions and operating conditions of a parabolic trough plant of 50 MWe, similar to Andasol 1 (Granada, Spain). The performance evaluation of each of the proposed prototypes is virtually tested by means of a numerical methodology which considers the heat transfer and fluid dynamics phenomena present in these devices. Two sets of cases are considered, one with the objective of testing the TES systems individually, by defining specific operating conditions and taking the systems to a periodic steady state; and another, aiming to evaluate their performance after several days of operation in a CSP plant, in which the weather variability and the thermal behavior of the tank walls and foundation are simulated. Thermal performance parameters, such as total energy and exergy stored/released and the efficiency in the use of the storage capacity, are calculated and compared with those obtained by other thermocline-like configurations (single-solid and single-PCM), and with a reference 2-tank molten-salt system. Obtained results allow to continue considering the MLSPCM concept as an interesting alternative for thermal storage in CSP facilities.Multi-layered solid-PCM thermocline thermal storage concept for CSP plants. Numerical analysis and perspectives
http://hdl.handle.net/2117/76330
Multi-layered solid-PCM thermocline thermal storage concept for CSP plants. Numerical analysis and perspectives
Galione Klot, Pedro Andrés; Pérez Segarra, Carlos David; Rodríguez Pérez, Ivette María; Oliva Llena, Asensio; Rigola Serrano, Joaquim
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 concentrated solar power (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-like storage concept, which aims at circumventing this issue. The proposed concept consists of a storage tank filled with a combination of solid material and encapsulated PCMs, forming a multi-layered packed bed, with molten salt as the 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 periodic state is achieved, i.e. when the same amount of energy is stored/released in consecutive charging/discharging cycles. As a result, the dependence of the storage capacity on the PCMs temperatures, the total energy and exergy stored/released, as well as the efficiencies of the storing process are compared for the different thermocline, single PCM, cascaded PCM and the proposed multi-layered solid-PCM (MLSPCM) configurations. The analysis shows that the multi-layered solid-PCM concept is a promising alternative for thermal storage in CSP plants.
2015-07-27T09:58:03ZGalione Klot, Pedro AndrésPérez Segarra, Carlos DavidRodríguez Pérez, Ivette MaríaOliva Llena, AsensioRigola Serrano, JoaquimThermocline storage concept has been considered for more than a decade as a possible solution to reduce the huge cost of the storage system in concentrated solar power (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-like storage concept, which aims at circumventing this issue. The proposed concept consists of a storage tank filled with a combination of solid material and encapsulated PCMs, forming a multi-layered packed bed, with molten salt as the 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 periodic state is achieved, i.e. when the same amount of energy is stored/released in consecutive charging/discharging cycles. As a result, the dependence of the storage capacity on the PCMs temperatures, the total energy and exergy stored/released, as well as the efficiencies of the storing process are compared for the different thermocline, single PCM, cascaded PCM and the proposed multi-layered solid-PCM (MLSPCM) configurations. The analysis shows that the multi-layered solid-PCM concept is a promising alternative for thermal storage in CSP plants.A finite-volume/level-set method for simulating two-phase flows on unstructured grids
http://hdl.handle.net/2117/26121
A finite-volume/level-set method for simulating two-phase flows on unstructured grids
Balcázar Arciniega, Néstor; Jofre Cruanyes, Lluís; Lehmkuhl Barba, Oriol; Castro González, Jesús; Rigola Serrano, Joaquim
The conservative level-set method for capturing the interface between two fluids is combined with a variable density projection scheme to simulate incompressible two-phase flows on unstructured meshes. All equations are discretized by using a conservative finite-volume approximation on a collocated grid arrangement. A high order scheme based on a flux limiter formulation, is adopted for approximating the convective terms, while the diffusive fluxes are centrally differenced. Gradients are computed by the least-squares approach. Physical properties are assumed to vary smoothly in a narrow band around the interface to avoid numerical instabilities. The numerical method is validated against classical advection test and two-phase flow examples including topology changes.
2015-01-27T15:18:32ZBalcázar Arciniega, NéstorJofre Cruanyes, LluísLehmkuhl Barba, OriolCastro González, JesúsRigola Serrano, JoaquimThe conservative level-set method for capturing the interface between two fluids is combined with a variable density projection scheme to simulate incompressible two-phase flows on unstructured meshes. All equations are discretized by using a conservative finite-volume approximation on a collocated grid arrangement. A high order scheme based on a flux limiter formulation, is adopted for approximating the convective terms, while the diffusive fluxes are centrally differenced. Gradients are computed by the least-squares approach. Physical properties are assumed to vary smoothly in a narrow band around the interface to avoid numerical instabilities. The numerical method is validated against classical advection test and two-phase flow examples including topology changes.Unsteady forces on a circular cylinder at critical Reynolds numbers
http://hdl.handle.net/2117/25143
Unsteady forces on a circular cylinder at critical Reynolds numbers
Lehmkuhl Barba, Oriol; Rodríguez Pérez, Ivette María; Borrell, Ricard; Chiva Segura, Jorge; Oliva Llena, Asensio
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. 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 the present work, large-eddy simulations of the flow past a cylinder at Reynolds numbers in the range 2.5 × 105-6.5 × 105 are performed. It is shown how the pressure distribution changes as the Reynolds number increases in an asymmetric manner, occurring first on one side of the cylinder and then on the other side to complete the drop in the drag up to 0.23 at Re = 6.5 × 105. These variations in the pressure profile are accompanied by the presence of a small recirculation bubble, observed as a small plateau in the pressure, and located around ¿ = 105° (measured from the stagnation point). This small recirculation bubble anticipated by the experimental measurements is here well captured by the present computations and its position and size measured at every Reynolds number. The changes in the wake configuration as the Reynolds number increases are also shown and their relation to the increase in the vortex shedding frequency is discussed. The power spectra for the velocity fluctuations are computed. The analysis of the resulting spectrum showed the footprint of Kelvin-Helmholtz instabilities in the whole range. It is found that the ratio of these instabilities frequency to the primary vortex shedding frequency matches quite well the scaling proposed by Prasad and Williamson [“The instability of the separated shear layer from a bluff body,” Phys. Fluids 8, 1347 (1996); “The instability of the shear layer separating from a bluff body,” J. Fluid Mech. 333, 375–492 (1997)] (f KH /fvs ¿ Re 0.67).
2014-12-29T09:40:53ZLehmkuhl Barba, OriolRodríguez Pérez, Ivette MaríaBorrell, RicardChiva Segura, JorgeOliva Llena, AsensioIt 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. 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 the present work, large-eddy simulations of the flow past a cylinder at Reynolds numbers in the range 2.5 × 105-6.5 × 105 are performed. It is shown how the pressure distribution changes as the Reynolds number increases in an asymmetric manner, occurring first on one side of the cylinder and then on the other side to complete the drop in the drag up to 0.23 at Re = 6.5 × 105. These variations in the pressure profile are accompanied by the presence of a small recirculation bubble, observed as a small plateau in the pressure, and located around ¿ = 105° (measured from the stagnation point). This small recirculation bubble anticipated by the experimental measurements is here well captured by the present computations and its position and size measured at every Reynolds number. The changes in the wake configuration as the Reynolds number increases are also shown and their relation to the increase in the vortex shedding frequency is discussed. The power spectra for the velocity fluctuations are computed. The analysis of the resulting spectrum showed the footprint of Kelvin-Helmholtz instabilities in the whole range. It is found that the ratio of these instabilities frequency to the primary vortex shedding frequency matches quite well the scaling proposed by Prasad and Williamson [“The instability of the separated shear layer from a bluff body,” Phys. Fluids 8, 1347 (1996); “The instability of the shear layer separating from a bluff body,” J. Fluid Mech. 333, 375–492 (1997)] (f KH /fvs ¿ Re 0.67).Direct numerical simulation of the flow over a sphere at Re = 3700
http://hdl.handle.net/2117/23986
Direct numerical simulation of the flow over a sphere at Re = 3700
Rodríguez Pérez, Ivette María; Borrell Pol, Ricard; Lehmkuhl Barba, Oriol; Pérez Segarra, Carlos David; Oliva Llena, Asensio
The direct numerical simulation of the flow over a sphere is performed. The computations are carried out in the sub-critical regime at Re = 3700 (based on the free-stream velocity and the sphere diameter). A parallel unstructured symmetry-preserving formulation is used for simulating the flow. At this Reynolds number, flow separates laminarly near the equator of the sphere and transition to turbulence occurs in the separated shear layer. The vortices formed are shed at a large-scale frequency, St = 0.215, and at random azimuthal locations in the shear layer, giving a helical-like appearance to the wake. The main features of the flow including the power spectra of a set of selected monitoring probes at different positions in the wake of the sphere are described and discussed in detail. In addition, a large number of turbulence statistics are computed and compared with previous experimental and numerical data at comparable Reynolds numbers. Particular attention is devoted to assessing the prediction of the mean flow parameters, such as wall-pressure distribution, skin friction, drag coefficient, among others, in order to provide reliable data for testing and developing statistical turbulence models. In addition to the presented results, the capability of the methodology used on unstructured grids for accurately solving flows in complex geometries is also pointed out.
2014-09-05T10:25:08ZRodríguez Pérez, Ivette MaríaBorrell Pol, RicardLehmkuhl Barba, OriolPérez Segarra, Carlos DavidOliva Llena, AsensioThe direct numerical simulation of the flow over a sphere is performed. The computations are carried out in the sub-critical regime at Re = 3700 (based on the free-stream velocity and the sphere diameter). A parallel unstructured symmetry-preserving formulation is used for simulating the flow. At this Reynolds number, flow separates laminarly near the equator of the sphere and transition to turbulence occurs in the separated shear layer. The vortices formed are shed at a large-scale frequency, St = 0.215, and at random azimuthal locations in the shear layer, giving a helical-like appearance to the wake. The main features of the flow including the power spectra of a set of selected monitoring probes at different positions in the wake of the sphere are described and discussed in detail. In addition, a large number of turbulence statistics are computed and compared with previous experimental and numerical data at comparable Reynolds numbers. Particular attention is devoted to assessing the prediction of the mean flow parameters, such as wall-pressure distribution, skin friction, drag coefficient, among others, in order to provide reliable data for testing and developing statistical turbulence models. In addition to the presented results, the capability of the methodology used on unstructured grids for accurately solving flows in complex geometries is also pointed out.Large eddy and direct numerical simulations of a turbulent water-filled differentially heated cavity of aspect ratio 5
http://hdl.handle.net/2117/23641
Large eddy and direct numerical simulations of a turbulent water-filled differentially heated cavity of aspect ratio 5
Kizildag, Deniz; Trias Miquel, Francesc Xavier; Rodríguez Pérez, Ivette María; Oliva Llena, Asensio
Natural convection in a differentially heated cavity is characterized by different phenomena such as laminar to turbulent flow transition in the boundary layer, turbulent mixing, and thermal stratification in the
core of the cavity. In order to predict the thermal and fluid dynamic behavior of the flow in these cavities, the location of transition to turbulence should be accurately determined. In this work, the performance of three subgrid-scale (SGS) models is submitted to investigation in a water-filled cavity of aspect ratio 5 at
Rayleigh number Ra=3e11. To do so, the models are compared with the solution obtained by means of direct numerical simulation. The models tested are: (i) the wall-adapting local-eddy viscosity (WALE)
model, (ii) the QR model, (iii) the WALE model within a variational multiscale framework (VMS-WALE).
It has been shown that the VMS-WALE and WALE models perform better in estimating the location of transition to turbulence, and thus their overall behavior is more accurate than the QR model. The results have also revealed that the use of SGS models is justified in this flow as the transition location and consequently the flow structure cannot be captured properly if no model is used for the tested spatial resolution.
2014-07-28T10:57:08ZKizildag, DenizTrias Miquel, Francesc XavierRodríguez Pérez, Ivette MaríaOliva Llena, AsensioNatural convection in a differentially heated cavity is characterized by different phenomena such as laminar to turbulent flow transition in the boundary layer, turbulent mixing, and thermal stratification in the
core of the cavity. In order to predict the thermal and fluid dynamic behavior of the flow in these cavities, the location of transition to turbulence should be accurately determined. In this work, the performance of three subgrid-scale (SGS) models is submitted to investigation in a water-filled cavity of aspect ratio 5 at
Rayleigh number Ra=3e11. To do so, the models are compared with the solution obtained by means of direct numerical simulation. The models tested are: (i) the wall-adapting local-eddy viscosity (WALE)
model, (ii) the QR model, (iii) the WALE model within a variational multiscale framework (VMS-WALE).
It has been shown that the VMS-WALE and WALE models perform better in estimating the location of transition to turbulence, and thus their overall behavior is more accurate than the QR model. The results have also revealed that the use of SGS models is justified in this flow as the transition location and consequently the flow structure cannot be captured properly if no model is used for the tested spatial resolution.Flow and turbulent structures around simplified car models
http://hdl.handle.net/2117/23638
Flow and turbulent structures around simplified car models
Aljure Osorio, David E.; Lehmkuhl Barba, Oriol; Rodríguez Pérez, Ivette María; Oliva Llena, Asensio
External car aerodynamics study has great importance in overall car efficiency and ride stability, being a key element in successful automotive design. The flow over car geometries shows three dimensional and unsteady turbulent characteristics. Additionally, vortex shedding, flow reattachment and recirculation bubbles are also found around the bluff body. These phenomena greatly influence the lift and drag coefficients, which are fundamental for ride stability and energy efficiency, respectively. The aim of the present study is focused on the assessment of different LES models (e.g. VMS or SIGMA models), as well as to show their capabilities of capturing the large scale turbulent flow structures in car-like bodies using relative coarse grids. In order to achieve these objectives, the flow around two model car geometries, the Ahmed and the Asmo cars, is simulated. These generic bluff bodies reproduce the basic fluid dynamics features of real cars. First, the flow over both geometries is studied and compared against experimental results to validate the numerical results. Then, different LES models are used to study the flow in detail and compare the structures found in both geometries.
2014-07-28T10:15:53ZAljure Osorio, David E.Lehmkuhl Barba, OriolRodríguez Pérez, Ivette MaríaOliva Llena, AsensioExternal car aerodynamics study has great importance in overall car efficiency and ride stability, being a key element in successful automotive design. The flow over car geometries shows three dimensional and unsteady turbulent characteristics. Additionally, vortex shedding, flow reattachment and recirculation bubbles are also found around the bluff body. These phenomena greatly influence the lift and drag coefficients, which are fundamental for ride stability and energy efficiency, respectively. The aim of the present study is focused on the assessment of different LES models (e.g. VMS or SIGMA models), as well as to show their capabilities of capturing the large scale turbulent flow structures in car-like bodies using relative coarse grids. In order to achieve these objectives, the flow around two model car geometries, the Ahmed and the Asmo cars, is simulated. These generic bluff bodies reproduce the basic fluid dynamics features of real cars. First, the flow over both geometries is studied and compared against experimental results to validate the numerical results. Then, different LES models are used to study the flow in detail and compare the structures found in both geometries.Wind speed effect on the flow field and heat transfer around a parabolic trough solar collector
http://hdl.handle.net/2117/23266
Wind speed effect on the flow field and heat transfer around a parabolic trough solar collector
Amine Hachicha, Ahmed; Rodríguez Pérez, Ivette María; Oliva Llena, Asensio
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.
2014-06-18T16:17:39ZAmine Hachicha, AhmedRodríguez Pérez, Ivette MaríaOliva Llena, AsensioParabolic 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.Numerical investigation on the role of discrete element method in combined LBM-IBM-DEM modeling
http://hdl.handle.net/2117/23264
Numerical investigation on the role of discrete element method in combined LBM-IBM-DEM modeling
Zhang, Hao; Tan, Yuanqiang; Shu, Shi; niu, Xiaodong; Trias Miquel, Francesc Xavier; Yang, Dongmin; Li, Hao; Sheng, Yong
Particle collisions play a very important role in determining the fluid-particle multiphase flow, and thus it is crucial to treat the particle-particle interaction using a felicitous method in numerical simulations. A novel combined lattice Boltzmann method (LBM)-immersed boundary method (IBM)-discrete element method (DEM) scheme is presented in this study with its application to model the sedimentation of 2D circular particles in incompressible Newtonian flows. The hydrodynamic model of the incompressible Newtonian flow is based on the Bhatnagar-Gross-Krook LBM, and a momentum exchange-based IBM is adopted to calculate the fluid-solid interaction force. The kinematics and trajectory of the discrete particles are evaluated by DEM, in which the particle-particle interaction rules are governed by theoretical contact mechanics to enable the direct use of real particle properties. This eliminates the need of artificial parameters and also improves the reliability of the numerical results. By using a more accurate and physical description of particle interaction, a 'safe zone' or threshold is also no longer required. Case studies of single particle settling in a cavity, and two particles settling in a channel were carried out, the velocity characteristics of the particle during settling and near the bottom were examined. A numerical example of sedimentation involving 504 particles was finally presented to demonstrate the capability of the combined scheme.
2014-06-18T15:51:27ZZhang, HaoTan, YuanqiangShu, Shiniu, XiaodongTrias Miquel, Francesc XavierYang, DongminLi, HaoSheng, YongParticle collisions play a very important role in determining the fluid-particle multiphase flow, and thus it is crucial to treat the particle-particle interaction using a felicitous method in numerical simulations. A novel combined lattice Boltzmann method (LBM)-immersed boundary method (IBM)-discrete element method (DEM) scheme is presented in this study with its application to model the sedimentation of 2D circular particles in incompressible Newtonian flows. The hydrodynamic model of the incompressible Newtonian flow is based on the Bhatnagar-Gross-Krook LBM, and a momentum exchange-based IBM is adopted to calculate the fluid-solid interaction force. The kinematics and trajectory of the discrete particles are evaluated by DEM, in which the particle-particle interaction rules are governed by theoretical contact mechanics to enable the direct use of real particle properties. This eliminates the need of artificial parameters and also improves the reliability of the numerical results. By using a more accurate and physical description of particle interaction, a 'safe zone' or threshold is also no longer required. Case studies of single particle settling in a cavity, and two particles settling in a channel were carried out, the velocity characteristics of the particle during settling and near the bottom were examined. A numerical example of sedimentation involving 504 particles was finally presented to demonstrate the capability of the combined scheme.From extruded-2D to fully-3D geometries for DNS: a multigrid-based extension of the Poisson solver
http://hdl.handle.net/2117/21618
From extruded-2D to fully-3D geometries for DNS: a multigrid-based extension of the Poisson solver
Gorobets, Andrei; Trias Miquel, Francesc Xavier; Soria Guerrero, Manel; Pérez Segarra, Carlos David; Oliva Llena, Asensio
Direct numerical simulation (DNS) of incompressible flows is an essential tool for improving the understanding of the physics of turbulence and for the development of better turbulence models. The Poisson equation, the main bottleneck from a parallel point of view, usually also limits its applicability for complex geometries. In this context, efficient and scalable Poisson solvers on fully-3D geometries are of high interest.In our previous work, a scalable algorithm for Poisson equation was proposed. It performed well on both small clusters with poor network performance and supercomputers using efficiently up to a thousand of CPUs. This algorithm named Krylov-Schur-Fourier Decomposition (KSFD) can be used for problems in parallelepipedic 3D domains with structured meshes and obstacles can be placed inside the flow. However, since a FFT decomposition is applied in one direction, mesh is restricted to be uniform and obstacles to be 2D shapes extruded along this direction.The present work is devoted to extend the previous KSFD algorithm to eliminate these limitations. The extension is based on a two-level Multigrid (MG) method that uses KSFD as a solver for second level. The algorithm is applied for a DNS of a turbulent flow in a channel with wall-mounted cube. Illustrative results at Re τ = 590 (based on the cube height and the bulk velocity Re h = 7235) are shown.
2014-02-17T15:33:45ZGorobets, AndreiTrias Miquel, Francesc XavierSoria Guerrero, ManelPérez Segarra, Carlos DavidOliva Llena, AsensioDirect numerical simulation (DNS) of incompressible flows is an essential tool for improving the understanding of the physics of turbulence and for the development of better turbulence models. The Poisson equation, the main bottleneck from a parallel point of view, usually also limits its applicability for complex geometries. In this context, efficient and scalable Poisson solvers on fully-3D geometries are of high interest.In our previous work, a scalable algorithm for Poisson equation was proposed. It performed well on both small clusters with poor network performance and supercomputers using efficiently up to a thousand of CPUs. This algorithm named Krylov-Schur-Fourier Decomposition (KSFD) can be used for problems in parallelepipedic 3D domains with structured meshes and obstacles can be placed inside the flow. However, since a FFT decomposition is applied in one direction, mesh is restricted to be uniform and obstacles to be 2D shapes extruded along this direction.The present work is devoted to extend the previous KSFD algorithm to eliminate these limitations. The extension is based on a two-level Multigrid (MG) method that uses KSFD as a solver for second level. The algorithm is applied for a DNS of a turbulent flow in a channel with wall-mounted cube. Illustrative results at Re τ = 590 (based on the cube height and the bulk velocity Re h = 7235) are shown.