 Research group
 Heat and Mass Transfer Technological Center (CTTC)
 Department
 Department of Heat Engines
 School
 Terrassa School of Industrial and Aeronautical Engineering (ETSEIAT)
 xavicttc.upc.edu
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 UPC directory
 Orcid
 0000000259660703
 Scopus Author ID
 7801421397
Scientific and technological production


Large eddy and direct numerical simulations of a turbulent waterfilled differentially heated cavity of aspect ratio 5
Kizildag, Deniz; Trias Miquel, Francesc Xavier; Rodriguez Pérez, Ivette Maria; Oliva Llena, Asensio
International journal of heat and mass transfer
Vol. 77, p. 10841094
DOI: 10.1016/j.ijheatmasstransfer.2014.06.030
Date of publication: 20141001
Journal article
Read the abstract Access to the full text Share Reference managersNatural 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 subgridscale (SGS) models is submitted to investigation in a waterfilled cavity of aspect ratio 5 at Rayleigh number Ra = 3 x 10(11). To do so, the models are compared with the solution obtained by means of direct numerical simulation. The models tested are: (i) the walladapting localeddy viscosity (WALE) model, (ii) the QR model, (iii) the WALE model within a variational multiscale framework (VMSWALE). It has been shown that the VMSWALE and WALE models perform better in estimating the location of transition to turbulence, and thus their overall behavior is more accurate than the OR 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. (C) 2014 Elsevier Ltd. All rights reserved.
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 subgridscale (SGS) models is submitted to investigation in a waterfilled 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 walladapting localeddy viscosity (WALE) model, (ii) the QR model, (iii) the WALE model within a variational multiscale framework (VMSWALE). It has been shown that the VMSWALE 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. 
Numerical investigation on the role of discrete element method in combined LBMIBMDEM modeling
Zhang, Hao; Tan, Yuanqiang; Shu, Shi; Niu, Xiaodong; Trias Miquel, Francesc Xavier; Yang, Dongmin; Li, Hao; Sheng, Yong
Computers and fluids
Vol. 94, p. 3748
DOI: 10.1016/j.compfluid.2014.01.032
Date of publication: 20140501
Journal article
Read the abstract View Share Reference managersParticle collisions play a very important role in determining the fluidparticle multiphase flow, and thus it is crucial to treat the particleparticle 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 BhatnagarGrossKrook LBM, and a momentum exchangebased IBM is adopted to calculate the fluidsolid interaction force. The kinematics and trajectory of the discrete particles are evaluated by DEM, in which the particleparticle 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.
Particle collisions play a very important role in determining the fluidparticle multiphase flow, and thus it is crucial to treat the particleparticle 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 BhatnagarGrossKrook LBM, and a momentum exchangebased IBM is adopted to calculate the fluidsolid interaction force. The kinematics and trajectory of the discrete particles are evaluated by DEM, in which the particleparticle 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. 
Symmetrypreserving discretization of NavierStokes equations on collocated unstructured meshes
Trias Miquel, Francesc Xavier; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio; Perez Segarra, Carlos David; Verstappen, R.W.C.P.
Journal of computational physics
Vol. 258, p. 246267
DOI: 10.1016/j.jcp.2013.10.031
Date of publication: 20140201
Journal article
Read the abstract View Share Reference managersA fullyconservative discretization is presented in this paper. The same principles followed by Verstappen and Veldman (2003) are generalized for unstructured meshes. Here, a collocatedmesh scheme is preferred over a staggered one due to its simpler form for such meshes. The basic idea behind this approach remains the same: mimicking the crucial symmetry properties of the underlying differential operators, i.e., the convective operator is approximated by a skewsymmetric matrix and the diffusive operator by a symmetric, positivedefinite matrix. A novel approach to eliminate the checkerboard spurious modes without introducing any nonphysical dissipation is proposed. To do so, a fullyconservative regularization of the convective term is used. The supraconvergence of the method is numerically showed and the treatment of boundary conditions is discussed. Finally, the new discretization method is successfully tested for a buoyancydriven turbulent flow in a differentially heated cavity. 
Conservation properties of unstructured finitevolume mesh schemes for the NavierStokes equations
Jofre Cruanyes, Lluís; Lehmkuhl Barba, Oriol; Ventosa Molina, Jordi; Trias Miquel, Francesc Xavier; Oliva Llena, Asensio
Numerical heat transfer. Part B, fundamentals
Vol. 65, num. 1, p. 5379
DOI: 10.1080/10407790.2013.836335
Date of publication: 20131109
Journal article
Read the abstract View Share Reference managersThe NavierStokes equations describe fluid flow by conserving mass and momentum. There are two main mesh discretizations for the computation of these equations, the collocated and staggered schemes. Collocated schemes locate the velocity field at the same grid points as the pressure one, while staggered discretizations locate variables at different points within the mesh. One of the most important characteristic of the discretization schemes, aside from accuracy, is their capacity to discretely conserve kinetic energy, specially when solving turbulent flow. Hence, this work analyzes the accuracy and conservation properties of two particular collocated and staggered schemes by solving various problems. 
A parallel MPI+OpenMP+OpenCL algorithm for hybrid supercomputations of incompressible flows
Gorobets, Andrei; Trias Miquel, Francesc Xavier; Oliva Llena, Asensio
Computers and fluids
Vol. 88, p. 764772
DOI: 10.1016/j.compfluid.2013.05.021
Date of publication: 201312
Journal article
Read the abstract View Share Reference managersThe work is devoted to the development of efficient parallel algorithms for largescale simulations of incompressible flows on hybrid supercomputers based on massivelyparallel accelerators. The governing equations are discretized using a highorder finitevolume scheme for Cartesian staggered meshes with the only restriction that, at least, one direction is periodic. Its ¿classical¿ MPI + OpenMP parallel implementation for CPUs was designed to scale till 100,000 CPU cores. The new hybrid algorithm is developed on a base of a multilevel parallel model that exploits several layers of parallelism of a modern hybrid supercomputer. In this model, MPI and OpenMP are used on the first two levels to couple nodes of a supercomputer and to engage its CPU cores. Then, computing accelerators are further used by means of the hardware independent OpenCL computing standard. In this way, the implementation is adapted to a general computing model with central processors and math coprocessors. In this paper the work is focused on adapting the basic operations of the algorithm to architectures of Graphics Processing Units (GPU) without considering the multiGPU communication scheme. Technology of porting the code to OpenCL is described, certain optimization approaches are presented and relevant performance results obtaining up to 80¿90 GFLOPS on a GPU accelerator are demonstrated. Moreover, the experience with different GPU architectures is summarized and a comparison based on the particular application is given for AMD and NVIDIA GPUs as well as for CUDA and OpenCL frameworks. 
An openCLbased parallel CFD code for simulations on hybrid systems with massivelyparallel accelerators
Gorobets, Andrei; Trias Miquel, Francesc Xavier; Oliva Llena, Asensio
Procedia engineering
Vol. 61, p. 8186
DOI: 10.1016/j.proeng.2013.07.097
Date of publication: 2013
Journal article
Read the abstract View Share Reference managersA parallel finitevolume CFD algorithm for modeling of incompressible flows on hybrid supercomputers is presented. It is based on a symmetrypreserving highorder numerical scheme for structured meshes. A multilevel approach that combines different parallel models is used for largescale simulations on computing systems with massivelyparallel accelerators. MPI is used on the first level within the distributed memory model to couple computing nodes of a supercomputer. On the second level OpenMP is used to engage multiple CPU cores of a computing node. The third level exploits the computing potential of massivelyparallel accelerators such as GPU (Graphics Processing Units) of AMD and NVIDIA, or Intel Xeon Phi accelerators of the MIC (Many Integrated Core) architecture. The hardware independent OpenCL standard is used to compute on accelerators of different archi tectures within a general model for a combination of a central processor and a math coprocessor. 
DNS and regularization modeling of a turbulent differentially heated cavity of aspect ratio 5
Trias Miquel, Francesc Xavier; Gorobets, Andrei; Perez Segarra, Carlos David; Oliva Llena, Asensio
International journal of heat and mass transfer
Vol. 57, num. 1, p. 171182
DOI: 10.1016/j.ijheatmasstransfer.2012.09.064
Date of publication: 20130115
Journal article
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FI201310021: Turbulent flow around a square cylinder at high Reynolds numbers: direct numerical simulation and regularization modeling
Trias Miquel, Francesc Xavier
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FI201320018: Turbulent flow around a square cylinder at high Reynolds numbers: direct numerical simulation and regularization modeling
Trias Miquel, Francesc Xavier
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FI201330020: Turbulent flow through a square duct: direct numerical simulation and advanced turbulence modeling
Trias Miquel, Francesc Xavier
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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
Vol. 232, num. 1, p. 118135
DOI: 10.1016/j.jcp.2012.07.009
Date of publication: 20130101
Journal article
Read the abstract View Share Reference managersThe 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. 
A simple approach to discretize the viscous term with spatially varying (eddy)viscosity
Trias Miquel, Francesc Xavier; Gorobets, Andrei; Oliva Llena, Asensio
Journal of computational physics
Vol. 253, p. 405417
DOI: 10.1016/j.jcp.2013.07.021
Date of publication: 20131115
Journal article
Read the abstract View Share Reference managersA simple approach to discretize the viscous dissipation term in the incompressible Navier¿Stokes equations with spatially varying viscosity is presented. Unlike the case where the viscosity remains constant, its discretization may be quite cumbersome especially for highorder staggered formulations. To circumvent this problem, we propose an alternative form of the viscous term whose discretization is straightforward. Notice that this approach is also suitable for eddyviscosity models for LargeEddy Simulation. Moreover, since it is based on already available operators, it can be easily implemented on any structured or unstructured code. The (supra)convergence of the method is numerically shown on both a fourthorder Cartesian staggered and an unstructured collocated formulation.
A simple approach to discretize the viscous dissipation term in the incompressible Navier–Stokes equations with spatially varying viscosity is presented. Unlike the case where the viscosity remains constant, its discretization may be quite cumbersome especially for highorder staggered formulations. To circumvent this problem, we propose an alternative form of the viscous term whose discretization is straightforward. Notice that this approach is also suitable for eddyviscosity models for LargeEddy Simulation. Moreover, since it is based on already available operators, it can be easily implemented on any structured or unstructured code. The (supra)convergence of the method is numerically shown on both a fourthorder Cartesian staggered and an unstructured collocated formulation. 
Blending regularization and largeeddy simulation. From homogeneous isotropic turbulence to wind farm boundary layers
Folch Flórez, David; Trias Miquel, Francesc Xavier; Gorobets, Andrei; Oliva Llena, Asensio
European Turbulence Conference
Presentation's date: 201308
Presentation of work at congresses
Read the abstract View Share Reference managersThe incompressible NavierStokes equations form an excellent mathematical model for turbulent flows. However, direct simulations at high Reynolds numbers are not feasible because the convective term produces far too many relevant scales of motion. Therefore, in the foreseeable future numerical simulations of turbulent flows will have to resort to models of the small scales. Largeeddy simulation (LES) and regularization models are examples thereof. In the present work, we propose to combine both approaches. Restoring the Galilean invariance of the regularization method results into an additional hyperviscosity term. This approach provides a natural blending between regularization and LES. The performance of these recent improvements will be assessed through application to homogeneous isotropic turbulence, a turbulent channel flow and a windfarm turbulent boundary layer.
The incompressible NavierStokes equations form an excellent mathematical model for turbulent flows. However, direct simulations at high Reynolds numbers are not feasible because the convective term produces far too many relevant scales of motion. Therefore, in the foreseeable future numerical simulations of turbulent flows will have to resort to models of the small scales. Largeeddy simulation (LES) and regularization models are examples thereof. In the present work, we propose to combine both approaches. Restoring the Galilean invariance of the regularization method results into an additional hyperviscosity term. This approach provides a natural blending between regularization and LES. The performance of these recent improvements will be assessed through application to homogeneous isotropic turbulence, a turbulent channel flow and a windfarm turbulent boundary layer. 
New differential operators and discretization methods for eddyviscosity models for LES
Trias Miquel, Francesc Xavier; Gorobets, Andrei; Zhang, Hao; Oliva Llena, Asensio
International Conference on Parallel Computational Fluid Dynamics
p. 179184
Presentation's date: 20130522
Presentation of work at congresses
Read the abstract View Share Reference managersThe incompressible NavierStokes equations constitute an excellent mathematical modelization of turbulence. Unfortunately, at tempts at performing direct numerical simulations (DNS) are limited to relatively lowReynolds numbers. Therefore, dynamically less complex mathematical formulations are necessary for coarsegrain simulations. Eddyviscosity models for LargeEddy Sim ulation (LES) is an example thereof: they rely on differential operators that should be able to capture well different flow config urations (laminar and 2D flows, nearwall behavior, transitional regime...). In the present work, several differential operators are derived from the criterion that vortexstretching mechanism must stop at the smallest grid scale. Moreover, since the discretization errors may play an important role a novel approach to discretize the viscous term with spatially varying eddyviscosity is used. It is based on basic operators; therefore, the implementation is straightforward even for staggered formulations. The performance of the proposed models will be assessed by means of direct comparison to DNS reference results. 
An OpenCLbased parallel CFD code for simulations on hybrid systems with massivelyparallel accelerators
Gorobets, Andrei; Trias Miquel, Francesc Xavier; Oliva Llena, Asensio
International Conference on Parallel Computational Fluid Dynamics
p. 8186
Presentation's date: 20130523
Presentation of work at congresses
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Direct and largeeddy simulation of nonoberbeckboussinesq 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 LargeEddy Simulation
Presentation's date: 20130404
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Progress on eddyviscosity models for LES: new differential operators and discretization methods
Trias Miquel, Francesc Xavier; Verstappen, Roel; Gorobets, Andrei; Oliva Llena, Asensio
European Turbulence Conference
Presentation's date: 20130904
Presentation of work at congresses
Read the abstract View Share Reference managersThe incompressible NavierStokes equations constitute an excellent mathematical modelization of turbulence. Unfortunately, attempts at performing direct simulations are limited to relatively lowReynolds numbers. Therefore, dynamically less complex mathematical formulations are necessary for coarsegrain simulations. Eddyviscosity models for LargeEddy Simulation (LES) is an example thereof: they rely on differential operators that should be able to capture well different flow configurations (laminar and 2D flows, nearwall behavior, transitional regime...). In the present work, several differential operators are derived from the criterion that vortexstretching mechanism must stop at the smallest grid scale. Moreover, since the discretization errors may play a n important role a novel approach to discretize the viscous term with spatially varying eddyviscosity is used. It is based on basic operators; therefore, the implementation is straightforward even for staggered formulations. 
Acumulador de energía térmica en base a materiales de cambio de fase sólidolíquido 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: 20130301
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: 20130614
Invention patent
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FI201220020: Turbulent natural convection in enclosed cavities. On the role of transitional thermal boundary layers in the flow structure
Trias Miquel, Francesc Xavier
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FI201210014: Turbulent natural convection in enclosed cavities. On the role of transitional thermal boundary layers in the flow structure
Trias Miquel, Francesc Xavier
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FI201230020: Turbulent flow around a square cylinder at high Reynolds numbers: direct numerical simulation and regularization modeling
Trias Miquel, Francesc Xavier
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Numerical simulation of turbulence at lower cost: regularization modeling
Trias Miquel, Francesc Xavier; Gorobets, Andrey; Perez Segarra, Carlos David; Oliva Llena, Asensio
Computers and fluids
DOI: 10.1016/j.compfluid.2012.03.002
Date of publication: 20120313
Journal article
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An eulerianlagrangian modeling of fluidized bed
Zhang, Hao; YuanQiang, Tan; DongMin, Yang; Trias Miquel, Francesc Xavier; Sheng, Yong; Oliva Llena, Asensio
National Conference on Computational Mechanics of Granular Materials
p. 659663
Presentation's date: 20120917
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Spectrallyconsistent regularization modeling of turbulence and its connections with LES
Trias Miquel, Francesc Xavier
Connections Between Regularized and LargeEddy Simulation Methods for Turbulence
Presentation's date: 20120513
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EulerianLagrangian modeling of fluidized bed
Tan, Y; Zhang, Hao; Yang, D; Trias Miquel, Francesc Xavier; Sheng, Y.; Oliva Llena, Asensio
National Conference on Computational Mechanics of Granular Materials
Presentation's date: 20120614
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Spectrallyconsistent regularization modeling at very high Rayleigh numbers
Trias Miquel, Francesc Xavier; Verstappen, R.W.C.P.; Gorobets, Andrei; Oliva Llena, Asensio
International Symposium on Turbulence, Heat and Mass Transfer
Presentation's date: 20120919
Presentation of work at congresses
Read the abstract View Share Reference managersThe incompressible NavierStokes equations constitute an excellent mathematical modelization of turbulence. Unfortunately, attempts at performing direct simulations are limited to relatively lowRayleigh numbers because of the almost numberless small scales produced by the nonlinear convective term. Alternatively, a dynamically less complex formulation is proposed here. Namely, regularizations of the NavierStokes equations that preserve the symmetry and conservation properties exactly. To do so, both convective and diffusive term are altered in the same vein. In this way, the convective production of small scales is effectively restrained whereas the modified diffusive term introduces a hyperviscosity effect and consequently enhances the destruction of small scales. In practice, the only additional ingredient is a selfadjoint linear filter whose local filter length is determined from the requirement that vortexstretching must stop at the smallest grid scale. The performance of the novel regularization modeling approach is assessed through application to turbulent natural convection flows at very high Rayleigh numbers 
Towards the regularization modeling of wind farm boundary layers
Trias Miquel, Francesc Xavier; Folch, David; Gorobets, Andrey; Oliva Llena, Asensio
EUROMECH Colloquium
Presentation's date: 20120215
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Spectrallyconsistent regularization modeling of wind farm boundary layers
Trias Miquel, Francesc Xavier; Gorobets, Andrey; Folch, David; Oliva Llena, Asensio
Conference on Modelling Fluid Flow
p. 96103
Presentation's date: 20120906
Presentation of work at congresses
Read the abstract Access to the full text Share Reference managersThe incompressible NavierStokes equations constitute an excellent mathematical modelization of turbulence. Unfortunately, attempts at performing direct simulations are limited to relatively lowReynolds numbers because of the almost numberless small scales produced by the nonlinear convective term. Alternatively, a dynamically less complex formulation is proposed here. Namely, regularizations of the NavierStokes equations that preserve the symmetry and conservation properties exactly. To do so, both convective and diffusive term are altered in the same vein. In this way, the convective production of small scales is effectively restrained whereas the modified diffusive term introduces a hyperviscosity effect and consequently enhances the destruction of small scales. In practise, the only additional ingredient is a selfadjoint linear filter whose local filter length is determined from the requirement that vortexstretching must stop at the smallest grid scale. In the present work, the performance of the abovementioned recent improvements is assessed through application to homogeneous isotropic turbulence, a turbulent channel flow and a turbulent boundary layer. As a final application, regularization modelling will be applied for largescale numerical simulation of the atmospheric boundary layer through wind farms. 
Spectrallyconsistent regularization modeling of turbulent natural convection flows
Trias Miquel, Francesc Xavier; Verstappen, R.W.C.P.; Oliva Llena, Asensio; Gorobets, Andrei
European Thermal Sciences Conference
p. vol.395
DOI: 10.1088/17426596/395/1/012123
Presentation's date: 20120905
Presentation of work at congresses
Read the abstract Access to the full text Share Reference managersThe incompressible NavierStokes equations constitute an excellent mathematical modelization of turbulence. Unfortunately, attempts at performing direct simulations are limited to relatively lowReynolds numbers because of the almost numberless small scales produced by the nonlinear convective term. Alternatively, a dynamically less complex formulation is proposed here. Namely, regularizations of the NavierStokes equations that preserve the symmetry and conservation properties exactly. To do so, both convective and diffusive terms are altered in the same vein. In this way, the convective production of small scales is effectively restrained whereas the modified diffusive term introduces a hyperviscosity effect and consequently enhances the destruction of small scales. In practice, the only additional ingredient is a selfadjoint linear filter whose local filter length is determined from the requirement that vortexstretching must stop at the smallest grid scale. In the present work, the performance of the abovementioned recent improvements is assessed through application to turbulent natural convection flows by means of comparison with DNS reference data.
The incompressible NavierStokes equations constitute an excellent mathematical modelization of turbulence. Unfortunately, attempts at performing direct simulations are limited to relatively lowReynolds numbers because of the almost numberless small scales produced by the nonlinear convective term. Alternatively, a dynamically less complex formulation is proposed here. Namely, regularizations of the NavierStokes equations that preserve the symmetry and conservation properties exactly. To do so, both convective and diffusive terms are altered in the same vein. In this way, the convective production of small scales is effectively restrained whereas the modified diffusive term introduces a hyperviscosity effect and consequently enhances the destruction of small scales. In practice, the only additional ingredient is a selfadjoint linear filter whose local filter length is determined from the requirement that vortexstretching must stop at the smallest grid scale. In the present work, the performance of the abovementioned recent improvements is assessed through application to turbulent natural convection flows by means of comparison with DNS reference data. 
DNS and regularization modeling of a turbulent flow through a square duct up to Re _tau = 1200
Trias Miquel, Francesc Xavier; Gorobets, Andrei; Zhang, Hao; Oliva Llena, Asensio
International Conference on Parallel Computational Fluid Dynamics
p. 4849
Presentation's date: 20120520
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A parallel OpenCLbased solver for largescale DNS of incompressible flows on heterogenous systems
Trias Miquel, Francesc Xavier; Gorobets, Andrei; Oliva Llena, Asensio
International Conference on Parallel Computational Fluid Dynamics
p. 2223
Presentation's date: 20120520
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Sistema de almacenamiento de energía térmica combinando material sólido de calor sensible y material de cambio de fase
Oliva Llena, Asensio; Perez Segarra, Carlos David; Rigola Serrano, Joaquim; Castro Gonzalez, Jesus; Oliet Casasayas, Carles; Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Trias Miquel, Francesc Xavier; Capdevila Paramio, Roser; Galione Klot, Pedro Andres
Date of request: 20121227
Invention patent
Read the abstract Access to the full text Share Reference managersUn sistema para el almacenamiento y recuperación de energía térmica empleando como medio al menos un material de cambio de fase (sólidolíquido) y un material sólido de calor sensible que se encargan de almacenar/recuperar el calor obtenido desde una fuente externa en forma de calor sensible y calor latente de cambio de fase. Dichos materiales están debidamente contenidos en un único tanque, en cuyo interior existen al menos dos zonas, cada una conteniendo un material diferente, y diferenciadas por el rango de temperaturas a las que son sometidas. La configuración más usada consiste en tres diferentes zonas configuradas al interior del tanque: zona caliente, en la parte superior del tanque, donde un material de cambio de fase encapsulado caracterizado por una temperatura de fusión alta está encerrado; zona fría, ubicada en la parte inferior, donde un material de cambio de fase con baja temperatura de fusión está colocado; y una zona media, que contiene un material sólido de calor sensible. 
Symmetrypreserving regularization of wallbounded turbulent flows
Trias Miquel, Francesc Xavier; Gorobets, Andrey; Verstappen, Roel; Oliva Llena, Asensio
Journal of physics: conference series
Vol. 318, num. 4, p. 4260
DOI: 10.1088/17426596/318/4/042060
Date of publication: 2011
Journal article
Read the abstract Access to the full text Share Reference managersThe incompressible NavierStokes equations constitute an excellent mathematical modelization of turbulence. Unfortunately, attempts at performing direct simulations are limited to relatively lowReynolds numbers because of the almost numberless small scales produced by the nonlinear convective term. Alternatively, a dynamically less complex formulation is proposed here. Namely, regularizations of the NavierStokes equations that preserve the symmetry and conservation properties exactly. To do so, both convective and diffusive term are altered in the same vein. In this way, the convective production of small scales is effectively restrained whereas the modified diffusive term introduces an hyperviscosity effect and consequently enhances the destruction of small scales. In practice, the only additional ingredient is a selfadjoint linear filter whose local filter length is determined from the requirement that vortexstretching must stop at the smallest grid scale. To do so, a new criterion based on the invariants of the local strain tensor is proposed here. Altogether, the proposed method constitutes a parameterfree turbulence model.
The incompressible NavierStokes equations constitute an excellent mathematical modelization of turbulence. Unfortunately, attempts at performing direct simulations are limited to relatively lowReynolds numbers because of the almost numberless small scales produced by the nonlinear convective term. Alternatively, a dynamically less complex formulation is proposed here. Namely, regularizations of the NavierStokes equations that preserve the symmetry and conservation properties exactly. To do so, both convective and diffusive term are altered in the same vein. In this way, the convective production of small scales is effectively restrained whereas the modified diffusive term introduces an hyperviscosity effect and consequently enhances the destruction of small scales. In practice, the only additional ingredient is a selfadjoint linear filter whose local filter length is determined from the requirement that vortexstretching must stop at the smallest grid scale. To do so, a new criterion based on the invariants of the local strain tensor is proposed here. Altogether, the proposed method constitutes a parameterfree turbulence model. 
DESARROLLO CODIGOS Y ALGORITMOS PARALELOS ALTA PRESTACIONES FINES DISEÑO OPTIMIZADO SISTEMAS Y EQUIPOS TERMICOS
Perez Segarra, Carlos David; Trias Miquel, Francesc Xavier; Capdevila Paramio, Roser; Chiva Segura, Jorge; Gorobets, Andrey; Giraldez Garcia, Hector; Ventosa Molina, Jordi; Oliva Llena, Asensio
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FI201130019: Exploring new frontiers in turbulent natural convection flows
Trias Miquel, Francesc Xavier
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FI201120011: Exploring new frontiers in turbulent natural convection flows
Trias Miquel, Francesc Xavier
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FI201110013: Regularization Modeling of Turbulent Natural Convection Flows
Trias Miquel, Francesc Xavier
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On the construction of discrete filters for symmetrypreserving regularization models
Trias Miquel, Francesc Xavier; Verstappen, R.W.C.P.
Computers and fluids
Vol. 40, num. 1, p. 139148
DOI: 10.1016/j.compfluid.2010.08.015
Date of publication: 201101
Journal article
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Numerical investigation of the location of maximum erosive wear damage in elbow: Effect of slurry velocity, bend orientation and angle of elbow
Zhang, Hao; Tan, Yuanqiang; Yang, Dongmin; Trias Miquel, Francesc Xavier; Jiang, Shengqiang; Sheng, Yong; Oliva Llena, Asensio
Powder technology
Vol. 217, p. 467476
DOI: 10.1016/j.powtec.2011.11.003
Date of publication: 20110201
Journal article
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Hybrid MPI+OpenMP parallelization of an FFTbased 3D Poisson solver with one periodic direction
Gorobets, Andrey; Trias Miquel, Francesc Xavier; Borrell Pol, Ricard; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
Computers and fluids
Vol. 49, num. 1, p. 101109
DOI: 10.1016/j.compfluid.2011.05.003
Date of publication: 201110
Journal article
Read the abstract View Share Reference managersThis work is devoted to the development of efficient parallel algorithms for the direct numerical simulation (DNS) of incompressible flows on modern supercomputers. In doing so, a Poisson equation needs to be solved at each timestep to project the velocity field onto a divergencefree space. Due to the nonlocal nature of its solution, this elliptic system is the part of the algorithm that is most difficult to parallelize. The Poisson solver presented here is restricted to problems with one uniform periodic direction. It is a combination of a block preconditioned Conjugate Gradient (PCG) and an FFT diagonalization. The latter decomposes the original system into a set of mutually independent 2D systems that are solved by means of the PCG algorithm. For the most illconditioned systems, that correspond to the lowest Fourier frequencies, the PCG is replaced by a direct Schurcomplement based solver. The previous version of the Poisson solver was conceived for singlecore (also dualcore) processors and therefore, the distributed memory model with messagepassing interface (MPI) was used. The irruption of multicore architectures motivated the use of a twolevel hybrid MPI + OpenMP parallelization with the shared memory model on the second level. Advantages and implementation details for the additional OpenMP parallelization are presented and discussed in this paper. Numerical experiments show that, within its range of efficient scalability, the previous MPIonly parallelization is slightly outperformed by the MPI + OpenMP approach. But more importantly, the hybrid parallelization has allowed to significantly extend the range of efficient scalability. Here, the solver has been successfully tested up to 12800 CPU cores for meshes with up to 109 grid points. However, estimations based on the presented results show that this range can be potentially stretched up until 200,000 cores approximately. Finally, several examples of DNS simulations are briefly presented to illustrate some potential applications of the solver. 
Parallel direct Poisson solver for discretisations with one Fourier diagonalisable direction
Borrell Pol, Ricard; Lehmkuhl Barba, Oriol; Trias Miquel, Francesc Xavier; Oliva Llena, Asensio
Journal of computational physics
Vol. 230, num. 12, p. 47234741
DOI: 10.1016/j.jcp.2011.02.042
Date of publication: 20110601
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DNS and RANS modelling of a turbulent plane impinging jet
Jaramillo Ibarra, Julian Ernesto; Trias Miquel, Francesc Xavier; Gorobets, Andrey; Perez Segarra, Carlos David; Oliva Llena, Asensio
International journal of heat and mass transfer
Vol. 55, num. 4, p. 789801
DOI: 10.1016/j.ijheatmasstransfer.2011.10.031
Date of publication: 20110131
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A selfadaptive strategy for the time integration of NavierStokes equations
Trias Miquel, Francesc Xavier; Lehmkuhl Barba, Oriol
Numerical heat transfer. Part B, fundamentals
Vol. 60, num. 2, p. 116134
DOI: 10.1080/10407790.2011.594398
Date of publication: 201108
Journal article
Read the abstract View Share Reference managersAn efficient selfadaptive strategy for the explicit time integration of NavierStokes equations is presented. Unlike the conventional explicit integration schemes, it is not based on a standard CFL condition. Instead, the eigenvalues of the dynamical system are analytically bounded and the linear stability domain of the timeintegration scheme is adapted in order to maximize the time step. The method works independently of the underlying spatial mesh; therefore, it can be easily integrated into structured or unstructured codes. The additional computational cost is minimal, and a significant increase of the time step is achieved without losing accuracy. The effectiveness and robustness of the method are demonstrated on both a Cartesian staggered and an unstructured collocated formulation. In practice, CPU cost reductions up to more than 4 with respect to the conventional approach have been measured. 
Numerical simulation of turbulence at lower costs: regularization modeling
Trias Miquel, Francesc Xavier; Gorobets, Andrey; Soria Guerrero, Manel; Oliva Llena, Asensio
International Conference on Parallel Computational Fluid Dynamics
p. 15
Presentation's date: 20110507
Presentation of work at congresses
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Hybrid MPI+OpenMP parallelization of a NavierStokes solver for largescale DNS
Gorobets, Andrey; Trias Miquel, Francesc Xavier; Borrell Pol, Ricard; Soria Guerrero, Manel; Oliva Llena, Asensio
International Conference on Computational Heat and Mass Transfer
p. 15
Presentation's date: 20110707
Presentation of work at congresses
Read the abstract View Share Reference managersThis work presents a parallel NavierStokes solver for the largescale direct numerical simulation (DNS) of incompressible flows with one periodic direction. It is based on a scalable Poisson solver that combines an FFT diagonalization with a preconditioned conjugate gradient (PCG) method and a direct Schurcomplement based method. Modern architectures of supercomputers with multicore nodes motivate the use of a twolevel hybrid MPI+OpenMP parallelization. The use of the more complex twolevel approach has allowed to significantly extend the number of CPUs the solver can efficiently use. Here, the solver has been successfully tested on up to 12800 CPU cores for meshes with up to 109 grid points. However, estimations based on presented results show that more than 50000 CPU cores can potentially be exploited. 
FFTbased Poisson Solver for large scale numerical simulations of incompressible flows
Borrell Pol, Ricard; Lehmkuhl Barba, Oriol; Trias Miquel, Francesc Xavier; Oyarzun Altamirano, Guillermo; Oliva Llena, Asensio
International Conference on Parallel Computational Fluid Dynamics
p. 15
Presentation's date: 20110516
Presentation of work at congresses
Read the abstract Access to the full text Share Reference managersIn the context of timeaccurate numerical simulation of incompressible flows, a Poisson equation needs to be solved at least once per timestep to project the velocity field onto a divergencefree space. Due to the nonlocal nature of its solution, this elliptic system is one of the most time consuming and difficult to parallelise parts of the code. In this paper, a parallel direct Poisson solver restricted to problems with one uniform periodic direction is presented. It is a combination of a Direct Schurcomplement based Decomposition (DSD) and a Fourier diagonalisation. The latter decomposes the original system into a set of mutually independent 2D systems which are solved by means of the DSD algorithm. Since no restrictions are imposed in the nonperiodic directions, the overall algorithm is wellsuited for solving problems discretised on extruded 2D unstructured meshes. A new overall parallelisation strategy with respect to our earlier works is presented. This has allowed us to solve discrete Poisson equations with up to 109 grid points in less than half a second, using up to 8192 CPU cores of the MareNostrum Supercomputer.
Postprint (author’s final draft) 
Symmetrypreserving regularization of wallbounded turbulent flows
Trias Miquel, Francesc Xavier; Gorobets, Andrey; Verstappen, R.W.C.P.; Oliva Llena, Asensio
European Turbulence Conference
p. 110
DOI: 10.1088/17426596/318/4/042060
Presentation's date: 20110912
Presentation of work at congresses
Read the abstract View Share Reference managersThe incompressible NavierStokes equations constitute an excellent mathematical modelization of turbulence. Unfortunately, attempts at performing direct simulations are limited to relatively lowReynolds numbers because of the almost numberless small scales produced by the nonlinear convective term. Alternatively, a dynamically less complex formulation is proposed here. Namely, regularizations of the NavierStokes equations that preserve the symmetry and conservation properties exactly. To do so, both convective and diffusive term are altered in the same vein. In this way, the convective production of small scales is effectively restrained whereas the modified diffusive term introduces an hyperviscosity effect and consequently enhances the destruction of small scales. In practice, the only additional ingredient is a selfadjoint linear filter whose local filter length is determined from the requirement that vortexstretching must stop at the smallest grid scale. To do so, a new criterion based on the invariants of the local strain tensor is proposed here. Altogether, the proposed method constitutes a parameterfree turbulence model. 
Numerical simulation of particleladen turbulent flow using discrete element method
Zhang, Hou; Trias Miquel, Francesc Xavier; Oliva Llena, Asensio
International Conference on Particlebased Methods
p. 1
Presentation's date: 20111026
Presentation of work at congresses
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Numerical simulations of turbulent natural convection coupled and uncoupled with radiation
Capdevila Paramio, Roser; Lehmkuhl Barba, Oriol; Colomer Rey, Guillem; Trias Miquel, Francesc Xavier; Perez Segarra, Carlos David
International Conference on Computational Heat and Mass Transfer
p. 18
Presentation's date: 20110718
Presentation of work at congresses
Read the abstract View Share Reference managersIn the present work, turbulent natural convection in a tall differentially heated cavity of aspect ratio 5:1, filled with air (Pr = 0.7) under a Rayleigh number based on the height of 4.5 · 1010, is studied numerically. Two different situations have been analysed. In the first one, the cavity is filled with a transparent medium. In the second one, the cavity contains a grey participating gas. The turbulent flow is described by means of Large Eddy Simulation (LES) using symmetrypreserving discretizations. Simulations are compared with experimental data available in the literature and with Direct Numerical Simulations (DNS). Surface and gas radiation have been simulated using the Discrete Ordinates Method (DOM). The influence of radiation on fluid flow behaviour has also been analysed.
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