280 results on '"Assensi Oliva"'
Search Results
2. Unstructured Conservative Level-Set (UCLS) Simulations of Film Boiling Heat Transfer.
- Author
-
Néstor Balcázar-Arciniega, Joaquim Rigola, and Assensi Oliva
- Published
- 2023
- Full Text
- View/download PDF
Catalog
3. DNS of Thermocapillary Migration of a Bi-dispersed Suspension of Droplets.
- Author
-
Néstor Balcázar-Arciniega, Joaquim Rigola, and Assensi Oliva
- Published
- 2023
- Full Text
- View/download PDF
4. DNS of Mass Transfer in Bi-dispersed Bubble Swarms.
- Author
-
Néstor Balcázar-Arciniega, Joaquim Rigola, and Assensi Oliva
- Published
- 2022
- Full Text
- View/download PDF
5. An efficient eigenvalue bounding method: CFL condition revisited.
- Author
-
Francesc Xavier Trias, Xavier álvarez-Farré, àdel Alsalti-Baldellou, Andrey V. Gorobets, and Assensi Oliva
- Published
- 2024
- Full Text
- View/download PDF
6. Exploiting spatial symmetries for solving Poisson's equation.
- Author
-
àdel Alsalti-Baldellou, Xavier álvarez-Farré, Francesc Xavier Trias, and Assensi Oliva
- Published
- 2023
- Full Text
- View/download PDF
7. DNS of Mass Transfer from Bubbles Rising in a Vertical Channel.
- Author
-
Néstor Balcázar-Arciniega, Joaquim Rigola, and Assensi Oliva
- Published
- 2019
- Full Text
- View/download PDF
8. Spectrally-Consistent Regularization of Navier-Stokes Equations.
- Author
-
Francesc Xavier Trias, David Folch, Andrey V. Gorobets, and Assensi Oliva
- Published
- 2019
- Full Text
- View/download PDF
9. On the implementation of flux limiters in algebraic frameworks.
- Author
-
Nicolas Valle, Xavier álvarez-Farré, Andrey V. Gorobets, Jesús Castro, Assensi Oliva, and Francesc Xavier Trias
- Published
- 2022
- Full Text
- View/download PDF
10. Memory Aware Poisson Solver for Peta-Scale Simulations with one FFT Diagonalizable Direction.
- Author
-
Guillermo Oyarzun, Ricard Borrell, Francesc Xavier Trias, and Assensi Oliva
- Published
- 2017
- Full Text
- View/download PDF
11. DNS of the wall effect on the motion of bubble swarms.
- Author
-
Néstor Balcázar, Jesús Castro, Joaquim Rigola, and Assensi Oliva
- Published
- 2017
- Full Text
- View/download PDF
12. Efficient CFD code implementation for the ARM-based Mont-Blanc architecture.
- Author
-
Guillermo Oyarzun, Ricard Borrell, Andrey V. Gorobets, Filippo Mantovani, and Assensi Oliva
- Published
- 2018
- Full Text
- View/download PDF
13. Particulate Immersed Boundary Method for complex fluid-particle interaction problems with heat transfer.
- Author
-
Hao Zhang, Hai-Zhuan Yuan, Francesc Xavier Trias, Aibing Yu, Yuanqiang Tan, and Assensi Oliva
- Published
- 2016
- Full Text
- View/download PDF
14. An Efficient Eigenvalue Bounding Method: Cfl Condition Revisited
- Author
-
F. Xavier Trias, Xavier Álvarez-Farré, Àdel Alsalti-Baldellou, Andrey Gorobets, and Assensi Oliva
- Published
- 2023
- Full Text
- View/download PDF
15. Parallel load balancing strategy for Volume-of-Fluid methods on 3-D unstructured meshes.
- Author
-
Lluís Jofre, Ricard Borrell, Oriol Lehmkuhl, and Assensi Oliva
- Published
- 2015
- Full Text
- View/download PDF
16. Symmetry-preserving discretization of Navier-Stokes equations on collocated unstructured grids.
- Author
-
Francesc Xavier Trias, Oriol Lehmkuhl, Assensi Oliva, C. D. Pérez-Segarra, and R. W. C. P. Verstappen
- Published
- 2014
- Full Text
- View/download PDF
17. A simple approach to discretize the viscous term with spatially varying (eddy-)viscosity.
- Author
-
Francesc Xavier Trias, Andrey V. Gorobets, and Assensi Oliva
- Published
- 2013
- Full Text
- View/download PDF
18. Parallel direct Poisson solver for discretisations with one Fourier diagonalisable direction.
- Author
-
Rick Borrell, Oriol Lehmkuhl, Francesc Xavier Trias, and Assensi Oliva
- Published
- 2011
- Full Text
- View/download PDF
19. A direct Schur-Fourier decomposition for the efficient solution of high-order Poisson equations on loosely coupled parallel computers.
- Author
-
Francesc Xavier Trias, Manel Soria, C. D. Pérez-Segarra, and Assensi Oliva
- Published
- 2006
- Full Text
- View/download PDF
20. New Strategies for Mitigating the Gray Area in Delayed-Detached Eddy Simulation Models
- Author
-
Arnau Pont-Vílchez, Andrey Gorobets, Assensi Oliva, A. P. Duben, Alistair Revell, F. Xavier Trias, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
ComputerSystemsOrganization_COMPUTERSYSTEMIMPLEMENTATION ,Mathematics::Analysis of PDEs ,Direct numerical simulation ,Aerospace Engineering ,02 engineering and technology ,Computational fluid dynamics ,Boundary layer thickness ,01 natural sciences ,010305 fluids & plasmas ,Physics::Fluid Dynamics ,0203 mechanical engineering ,Incompressible flow ,0103 physical sciences ,Remolins (Mecànica de fluids) ,Turbulència ,Friction coefficient ,Physics ,020301 aerospace & aeronautics ,Mechanics ,Dinàmica de fluids computacional ,Vortex ,Turbulence ,Detached eddy simulation ,Reynolds-averaged Navier–Stokes equations ,Eddies ,Enginyeria mecànica::Mecànica de fluids [Àrees temàtiques de la UPC] - Abstract
This paper presents a new approach for mitigating the unphysical delay in the Reynolds-averaged Navier–Stokes (RANS) to large-eddy simulation (LES) transition, often referred to as the gray area, which is a common issue for hybrid RANS–LES turbulence models such as delayed-detached eddy simulation. An existing methodology designed for improving the LES performance in complex flows is adapted and tested. This is based on reducing the numerical diffusion in critical areas for permitting a more accurate development of turbulence. The new formulation comprises both a two-dimensional sensitive velocity gradient model and an alternative definition of the subgrid length scale, which are tested both individually and in tandem, and compared with the other formulations commonly used for addressing the gray area. Four test cases are examined, a flat plate, two variants of the incompressible backwardfacing step, and an open jet compressible case, all of which are selected to expose the adverse impact of numerical diffusion that this study seeks to address. Furthermore, the proposed changes are implemented in two different codes for the purpose of cross-validation. Encouraging results are observed, supporting the suitability of the new approach as a candidate for addressing the gray area issue in flows of this kind. This work was financially supported by the Ministerio de Economía y Competitividad, Spain (No. ENE2017-88697-R). A.P.V. was supported by an FI-DGR 2016 predoctoral contract (No. 2018FI_ B2_00072) financed by Generalitat de Catalunya, Spain. F.X.T. was supported by a Ramón y Cajal postdoctoral contract (No. RYC-2012- 11996) financed by the Ministerio de Economía y Competitividad, Spain. A.D. and A.G. were supported by Moscow Center for Fundamental and Applied Mathematics, Agreement with the Ministry of Science and Higher Education of the Russian Federation, No. 075- 15-2019-1623. The NOISEtte computations were carried out using the equipment of the shared research facilities of HPC computing resources at Lomonosov Moscow State University and the computing resources of the federal collective usage center Complex for Simulation and Data Processing for Mega-science Facilities at NRC “Kurchatov Institute” (http://ckp.nrcki.ru/). more...
- Published
- 2021
21. Numerical study of rising bubbles with path instability using conservative level-set and adaptive mesh refinement
- Author
-
Oscar Antepara, Assensi Oliva, Néstor Balcázar, Joaquim Rigola, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
Conservative level-set ,Path instability ,General Computer Science ,Discretization ,Computer science ,Bubbles--Dynamics ,Wobbling bubble ,Direct numerical simulation ,01 natural sciences ,010305 fluids & plasmas ,Physics::Fluid Dynamics ,symbols.namesake ,Simulació per ordinador ,0103 physical sciences ,Projection method ,Applied mathematics ,0101 mathematics ,Adaptive mesh refinement ,Eötvös number ,General Engineering ,Morton number ,Reynolds number ,010101 applied mathematics ,symbols ,Reduction (mathematics) ,Bombolles -- Dinàmica ,Enginyeria mecànica::Mecànica de fluids [Àrees temàtiques de la UPC] - Abstract
This paper focuses on three-dimensional direct numerical simulations of rising bubbles in the wobbling regime, and the study of its dynamical behavior for Eötvös number 1 ≤ Eo ≤ 10 and Morton number 1e−11 ≤ M ≤ 1e−9. The computational methodology is based on a mass Conservative Level-Set method, whereas the spatial discretization of the computational domain employs an Adaptive Mesh Refinement strategy for the reduction of computational resources. The Navier–Stokes equations are discretized using the finite-volume approach on a collocated unstructured mesh; the pressure-velocity coupling is solved using a classical fractional-step projection method. This methodology is applied to a series of verification and validation tests, which are compared with experiments and numerical results from the literature. Finally, buoyancy bubbles rising in the wobbling regime are researched at moderate to high Reynolds numbers (100 more...
- Published
- 2019
- Full Text
- View/download PDF
22. Numa-Aware Strategies for the Heterogeneous Execution of Spmv On Modern Supercomputers
- Author
-
F. X. Trias, Assensi Oliva, X. Álvarez-Farré, A. Gorobets, Universitat Politècnica de Catalunya. Doctorat en Enginyeria Tèrmica, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
NUMA ,SpMV ,Física::Termodinàmica [Àrees temàtiques de la UPC] ,High performance computing ,Heterogeneous computing ,Dinàmica de fluids computacional ,Computational fluid dynamics ,Sparse algebra ,High-performance computing ,Càlcul intensiu (Informàtica) ,Enginyeria mecànica::Mecànica de fluids [Àrees temàtiques de la UPC] - Abstract
The sparse matrix-vector product is a widespread operation amongst the scientific computing community. It represents the dominant computational cost in many large-scale simulations relying on iterative methods, and its performance is sensitive to the sparse pattern, the storage format, and kernel implementation, and the target computing architecture. In this work, we are devoted to the efficient execution of the sparse matrix-vector product on (potentially hybrid) modern supercomputers with non-uniform memory access configurations. A hierarchical parallel implementation is proposed to minimize the number of processes participating in distributed-memory parallelization. As a result, a single process per computing node is enough to engage all its hardware and ensure efficient memory access on manycore platforms. The benefits of this approach have been demonstrated on up to 9,600 cores of MareNostrum 4 supercomputer, at Barcelona Supercomputing Center. The work of A. Gorobets has been funded by the Russian Science Foundation, project 19- 11-00299. The work of X. Alvarez-Farr ´ e, F. X. Trias and A. Oliva has been financially supported ´ by the ANUMESOL project (ENE2017-88697-R) by the Spanish Research Agency (Ministerio de Economía y Competitividad, Secretaría de Estado de Investigacion, Desarrollo e Inno- ´ vacion), and the FusionCAT project (001-P-001722) by the Government of Catalonia (RIS3CAT ´ FEDER). The studies of this work have been carried out using the MareNostrum 4 supercomputer of the Barcelona Supercomputing Center (projects IM-2020-2-0029 and IM-2020-3-0030); the TSUBAME3.0 supercomputer of the Global Scientific Information and Computing Center at Tokyo Institute of Technology; the Lomonosov-2 supercomputer of the shared research facilities of HPC computing resources at Lomonosov Moscow State University; the K-60 hybrid cluster of the collective use center of the Keldysh Institute of Applied Mathematics. The authors thankfully acknowledge these institutions for the compute time and technical support. more...
- Published
- 2021
23. Subgrid-Scale Model Based On the Invariants of the Gradient Model Tensor
- Author
-
David Folch, F. X. Trias, Assensi Oliva, Andrey Gorobets, Universitat Politècnica de Catalunya. Doctorat en Enginyeria Tèrmica, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
Computer science ,SGS models ,Turbulence ,Algebra ,Physics::Fluid Dynamics ,Fluid dynamics ,Work (electrical) ,LES ,Dinàmica de fluids ,Tensor (intrinsic definition) ,Agency (sociology) ,Gradient model ,Scale model ,Turbulència ,Enginyeria mecànica::Mecànica de fluids [Àrees temàtiques de la UPC] - Abstract
The incompressible Navier-Stokes equations stand as the best mathematical model for turbulent flows. However, direct numerical simulations at high Reynolds numbers are not yet feasible because the convective term produces far too many relevant scales of motion, thus remaining limited to relatively low-Reynolds numbers. Dynamically less complex mathematical formulations have been developed for coarse-grain simulations, like the well known eddy-viscosity models. Most of these models are based on the combination of invariants of a symmetric tensor that depends on the gradient of the resolved velocity field, G = Ñu, and should properly detect different flow configurations (laminar and 2D flows, near-wall behavior, transitional regime, etc.). Brand-new models have been constructed considering the first three invariants of the symmetric tensor GGT with excellent results;1 hence, it is formally based on the lowest-order approximation of the subgrid stress tensor, t(u) = D2 12GGT +O(D4), i.e. the gradient model proposed by Clark.2 Furthermore, these models have been implemented on a pseudo-spectral algorithm with a fully-explicit second-order time-integration method.3 The performance of this special configuration has been successfully tested for decaying isotropic turbulence and a turbulent channel flow. It is currently being developed for a semi-infinite boundary layer with periodic conditions as a previous step to carry out wind farm simulations. Details of the implementation and numerical results will be presented. The work has been financially supported by a competitive R+D project (ENE2017-88697-R) by the Spanish Research Agency. The authors thankfully acknowledge these institutions. more...
- Published
- 2021
24. Tetrahedral adaptive mesh refinement for two-phase flows using conservative level-set method
- Author
-
Assensi Oliva, Oscar Antepara, Néstor Balcázar, Universitat Politècnica de Catalunya. Doctorat en Enginyeria Tèrmica, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
Finite element method ,Conservative level-set ,Tetrahedral mesh ,Applied Mathematics ,Mechanical Engineering ,Flux multifàsic ,Computational Mechanics ,Elements finits, Mètode dels ,Tetrahedral elements ,Finite-volume method ,01 natural sciences ,010305 fluids & plasmas ,Computer Science Applications ,Tetrahedral meshes ,Física::Física de fluids::Flux de fluids [Àrees temàtiques de la UPC] ,Adaptive mesh refinement ,010101 applied mathematics ,Mechanics of Materials ,Multiphase flows ,0103 physical sciences ,0101 mathematics ,Multiphase flow ,Humanities - Abstract
In this article, we describe a parallel adaptive mesh refinement strategy for two-phase flows using tetrahedral meshes. The proposed methodology consists of combining a conservative level-set method with tetrahedral adaptive meshes within a finite volume framework. Our adaptive algorithm applies a cell-based refinement technique and adapts the mesh according to physics-based refinement criteria defined by the two-phase application. The new adapted tetrahedral mesh is obtained from mesh manipulations of an input mesh: operations of refinement and coarsening until a maximum level of refinement is achieved. For the refinement method of tetrahedral elements, geometrical characteristics are taking into consideration to preserve the shape quality of the subdivided elements. The present method is used for the simulation of two-phase flows, with surface tension, to show the capability and accuracy of 3D adapted tetrahedral grids to bring new numerical research in this context. Finally, the applicability of this approach is shown in the study of the gravity-driven motion of a single bubble/droplet in a quiescent viscous liquid on regular and complex domains. This work has been financially supported by the Ministerio de Economía y Competitividad, Secretaría de Estado de Investigación, Desarrollo e Innovación, Spain (ENE2017-88697-R), and by Termo Fluids S.L. Oscar Antepara acknowledges financial support in form of a doctoral scholarship DI-14-06886 of the Ministerio de Economía y Competitividad and 2015DI-68 of the Secretaria d’ Universitats i Recerca del Departament d’Economia i Coneixement de la Generalitat de Catalunya, Spain. Néstor Balcázar acknowledges financial support of the Programa Torres Quevedo, Ministerio de Economía y Competitividad, Secretaría de Estado de Investigación, Desarrollo e Innovación (PTQ-14-07186), Spain. Three-dimensional simulations were carried out using computer time provided by PRACE 14th Call (Project 2016153612) and RES project(FI-2018-1-0025) through the MareNostrum IV supercomputer based in Barcelona, Spain. We acknowledge Santander Supercomputacion support group at the University of Cantabria who provided access to the supercomputer Altamira Supercomputer at the Institute of Physics of Cantabria (IFCA-CSIC), member of the Spanish Supercomputing Network, for performing simulations/analyses (RES project FI-2018-3-0037). more...
- Published
- 2021
25. A CFD-based surrogate model for predicting flow parameters in a ventilated room using sensor readings
- Author
-
Nina Morozova, Francesc Xavier Trias, Roser Capdevila, Eugenio Schillaci, Assensi Oliva, Universitat Politècnica de Catalunya. Doctorat en Enginyeria Tèrmica, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
Mechanical Engineering ,Indoor air pollution ,Dinàmica de fluids computacional ,Ventilació ,Building and Construction ,Computational fluid dynamics ,Ventilation ,Indoor airflow prediction ,Physics::Fluid Dynamics ,Surrogate models ,Machine learning ,Mixed convection ,Electrical and Electronic Engineering ,Enginyeria mecànica::Mecànica de fluids [Àrees temàtiques de la UPC] ,Contaminació de l'ambient interior ,Civil and Structural Engineering - Abstract
In this work, we develop a computational fluid dynamics (CFD)-based surrogate model, which predicts flow parameters under different geometrical configurations and boundary conditions in a benchmark case of a mechanically ventilated room with mixed convection. The model inputs are the temperature and velocity values in different locations, which act as a surrogate of the sensor readings. The model’s output is a set of comfort-related flow parameters, such as the average Nusselt number on the hot wall, jet separation point, average kinetic energy, average enstrophy, and average temperature. We tested four different machine learning methods, among which we chose the gradient boosting regression due to its accurate performance. We also adapted the developed model for indoor environment control applications by determining the optimal combinations of sensor positions which minimize the prediction error. This model does not require the repetition of CFD simulations in order to be applied since the structure of the input data imitates sensor readings. Furthermore, the low computational cost of the model execution and good accuracy makes it an effective alternative to CFD for applications where rapid predictions of complex flow configurations are required, such as model predictive control. more...
- Published
- 2022
- Full Text
- View/download PDF
26. A GPU Accelerated Framework for Partitioned Solution of Fluid-Structure Interaction Problems
- Author
-
Assensi Oliva, Amin Totounferoush, Miriam Mehl, Alireza Naseri, J. Chiva, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
Computer science ,Simulació per ordinador ,Fluid–structure interaction ,Fluid-structure interaction ,Interacció fluid-estructura ,Computer simulation ,Hybrid CPU-GPU architectures ,Partitioned simulation ,Computational science ,Enginyeria mecànica::Mecànica de fluids [Àrees temàtiques de la UPC] - Abstract
We present a GPU-accelerated solver for the partitioned solution of fluid-structure interaction (FSI) problems. Independent scalable fluid and structure solvers are coupled by a library which handles the inter-code data communication, mapping and equation coupling. A coupling strategy is incorporated which allows accelerating expensive components of the coupled framework by offloading them to GPUs. To prove the efficiency of the proposed coupling strategy in conjunction with the offloading scheme, we present a numerical performance analysis for a complex test case in the filed of biomedical engineering. The numerical experiments demonstrate an excellent speed-up in the accelerated kernels (up to 133 times) which results in 6 to 8 times faster overall simulations. In addition, we observed a very good reduction in total simulation time by increasing the exploited compute nodes up to 8 (complete machine capacity). We thank the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) for supporting this work by funding - EXC2075 – 390740016 under Germany’s Excellence Strategy. We acknowledge the support by the Stuttgart Center for Simulation Science (SimTech). This work was also financially supported by • priority program 1648 - Software for Exascale Computing 214 (ExaFSA - Exascale Simulation of Fluid-Structure-Acoustics Interactions) of the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation), • Ministerio de Economía y Competitividad, Secretaría de Estado de Investigacion, Desarrollo e ´ Innovacion, Spain (ENE2017-88697-R). ´ The performance measurements were carried out on the Vulcan cluster at the High-Performance Computing Center Stuttgart (HLRS). The authors wish to thank HLRS for compute time and technical support. more...
- Published
- 2021
27. Investigating the capabilities of CFD-based data-driven models for indoor environmental design and control
- Author
-
N. Morozova, R. Capdevila, F. X. Trias, Assensi Oliva, Universitat Politècnica de Catalunya. Doctorat en Enginyeria Tèrmica, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
Turbulence Modeling ,Computer science ,business.industry ,Control (management) ,Indoor Environmental Applications ,Environmental design ,Computational Fluid Dynamics ,Dinàmica de fluids computacional ,Ventilació ,Computational fluid dynamics ,Mixed Convection ,Ventilation ,Data-driven ,Data Driven Models ,Turbulence ,Systems engineering ,business ,Turbulència ,Enginyeria mecànica::Mecànica de fluids [Àrees temàtiques de la UPC] - Abstract
In this work, we study the accuracy of CFD-based data-driven models, which predict comfort-related flow parameters in a ventilated cavity with a heated floor. We compare the computational cost and accuracy of three different models, namely artificial neural network, support vector regression, and gradient boosting regression. The tested scenarios include short and long cavities with different inlet velocities. Among the studied frameworks, the artificial neural network provides the most accurate predictions for most of the tested flow configurations. However, test configurations with jet separation and a secondary vortex are more difficult to predict correctly; thus more high-fidelity data is required in order to construct a more robust and reliable model. This work is supported by the Ministerio de Economía y Competitividad, Spain [ENE2017-88697-R]. N. Morozova is supported by the by the Ministerio de Economía y Competitividad, Spain [FPU16/06333 predoctoral contract]. Part of the calculations was performed on the MareNostrum 4 supercomputer at the Barcelona Supercomputing Center [RES project IM-2021-1-0015]. The authors thankfully acknowledge these institutions. more...
- Published
- 2021
28. Numerical Investigation On Fluid Flow of Protruding Branching Duct in a Dividing Junction of a Minichannel Heat Exchanger
- Author
-
Assensi Oliva, C. Oliet, Mohamed Settati, Universitat Politècnica de Catalunya. Doctorat en Enginyeria Tèrmica, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
Protruding branch ,Materials science ,Flux laminar ,Mechanics ,Calor -- Transmissió ,Branching (polymer chemistry) ,Laminar flow ,Dividing junction ,Distribution manifold ,Enginyeria mecànica [Àrees temàtiques de la UPC] ,medicine.anatomical_structure ,Fluid dynamics ,Dinàmica de fluids ,Heat exchanger ,medicine ,Heat -- Transmission ,Minichannel heat exchanger ,Duct (anatomy) - Abstract
This study focuses on investigating the effect of protruding branching duct on laminar fluid field in 90◦ dividing pipe junction of mini heat exchanger. The ducts under study, main and branch side, are of minichannel scale where the corresponding diameters are 3.96 and 1.6 mm respectively. First, numerical validations are given based on the experimental measurements of Cho et al. [1] for the case of non-protruding branching duct (h=0, β ≠0) and also comparing with Poiseuille flow for nonprotruding case with no flow in the branch side (h=0, β=0) where good agreements were found in each case. Second, the degree of protrusion in pipe branching duct is characterized studying and analyzing two cases of protrusions (h = D1/4 and h = D1/2). The effects of branching flow rate ratio β on local pressure changes and the velocity profile are presented and examined in both main and branching ducts. Finally, the influence of the extent of protruded branch on velocity field and the local pressure drop are documented as expected. The results shown a strong effect of protrusion on hydrodynamic flow more...
- Published
- 2021
- Full Text
- View/download PDF
29. On a Proper Tensorial Subgrid Heat Flux Model
- Author
-
F. Dabbagh, Assensi Oliva, A. Gorobets, F. X. Trias, D. Santos, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, Universitat Politècnica de Catalunya. Doctorat en Enginyeria Tèrmica, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
Physics ,Física::Termodinàmica [Àrees temàtiques de la UPC] ,Mechanics ,Dinàmica de fluids computacional ,Computational fluid dynamics ,Calor -- Transmissió ,SGS models ,Physics::Fluid Dynamics ,Turbulence ,Heat flux ,LES ,Heat -- Transmission ,Buoyancy-driven flows ,Remolins (Mecànica de fluids) ,Eddies ,Enginyeria mecànica::Mecànica de fluids [Àrees temàtiques de la UPC] ,Turbulència - Abstract
In this work, we aim to shed light to the following research question: can we find a nonlinear tensorial subgrid-scale (SGS) heat flux model with good physical and numerical properties, such that we can obtain satisfactory predictions for buoyancy-driven turbulent flows? This is motivated by our findings showing that the classical (linear) eddy-diffusivity assumption, q eddy ¿ ¿T, fails to provide a reasonable approximation for the actual SGS heat flux, q = uT - uT: namely, a priori analysis for airfilled Rayleigh-Bénard convection (RBC) clearly shows a strong misalignment. In the quest for more accurate models, we firstly study and confirm the suitability of the eddy-viscosity assumption for RBC carrying out a posteriori tests for different models at very low Prandtl numbers (liquid sodium, Pr = 0.005) where no heat flux SGS activity is expected. Then, different (nonlinear) tensor-diffusivity SGS heat flux models are studied a priori using DNS data of an air-filled (Pr = 0.7) RBC at Rayleigh numbers up to 1011. Apart from having good alignment trends with the actual SGS heat flux, we also restrict ourselves to models that are numerically stable per se and have the proper cubic near-wall behavior. This analysis leads to a new family of SGS heat flux models based on the symmetric positive semi-definite tensor GGT where G = ¿u, i.e. q ¿ GGT¿T, and the invariants of the GGT tensor. Finally, relevant numerical aspects regarding the implementation of this type of models are discussed in detail. A list of physical and numerical properties is identified and subsequently imposed, leading to a symmetrypreserving discretization that is based on discrete operators already available in any CFD code. F.X.T., F.D. and A.O. have been financially supported by the Ministerio de Economía y Competitividad, Spain, ANUMESOL project (ENE2017-88697-R). F.X.T. and A.O. are supported by the Generalitat de Catalunya RIS3CAT-FEDER, FusionCAT project (001-P-001722). F.D. is supported by the Austrian Federal Ministry for Digital and Economic Affairs, the National Foundation for Research, Technology and Development, and the K1MET center for metallurgical research in Austria (www.k1-met.com). D.S. is supported by an FI AGAUR-Generalitat de Catalunya fellowship (2020FI B 00839). Calculations have been performed on the IBM MareNostrum 4 supercomputer at the BSC (PRACE 15th Call, Ref. 2016163972, “Exploring new frontiers in Rayleigh-Bénard convection” and Tier-1 RES projects IM-2020-2-0029 & IM-2020-3-0030 “Direct and Large-Eddy Simulation of buoyancy-driven turbulence in liquid metals”). The authors thankfully acknowledge these institutions. more...
- Published
- 2021
30. On Preconditioning Variable Poisson Equation with Extreme Contrasts in the Coefficients
- Author
-
A. Gorobets, À. Alsalti-Baldellou, F. X. Trias, Assensi Oliva, Universitat Politècnica de Catalunya. Doctorat en Enginyeria Tèrmica, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
Variable Preconditioning ,Enginyeria mecànica [Àrees temàtiques de la UPC] ,Variables (Mathematics) ,Flux multifàsic ,Mathematical analysis ,Poisson Equation ,Multiphase Flow ,Poisson's equation ,Adaptive Mesh Refinement ,Variables (Matemàtica) ,Variable (mathematics) ,Mathematics - Abstract
It is well known that the solution by means of iterative methods of very ill-conditioned systems leads to very poor convergence rates. In this context, preconditioning becomes crucial in order to modify the spectrum of the system being solved and improve the performance of the solvers. A proper balance between the reduction in the number of iterations and the overhead of the construction and application of the preconditioner needs to be sought to actually decrease the total execution time of the solvers. This is particularly important when considering variable coefficients matrices as, in general, its preconditioners will also be variable and need to be updated regularly at an affordable cost. In this work we present a family of variable preconditioners designed for the effective solution of variable Poisson equation with extreme contrasts in the coefficients, which represents a particularly challenging case as it translates into a variable and extremely ill-conditioned system arising in many situations such as with multiphase flows presenting high density ratios or in the presence of highly-stretched adaptive mesh refinements. Finally, the results of the numerical experiments performed are presented and discussed, confirming our preconditioners as extremely affordable, highly-parallelizable and easy-to-implement alternatives to the more standard (and usually unfeasible) preconditioners, still showing great improvements in the rate of convergence of the solvers without requiring the variable coefficients matrix to be explicitly rebuilt at each iteration. Àdel Alsalti-Baldellou, F. Xavier Trias and Assensi Oliva have been financially supported by a competitive R+D project (ENE2017-88697-R) by the Spanish Research Agency. Àdel Alsalti-Baldellou is also supported by predoctoral grants DIN2018-010061 and 2019-DI-90, given by, respectively, the Spanish Ministry of Science, Innovation and Universities (MICINN) and the Catalan Agency for Management of University and Research Grants (AGAUR). more...
- Published
- 2021
31. Three-Dimensional Direct Numerical Simulation (DNS) of Taylor Bubbles Rising in Non-Newtonian Environments
- Author
-
J. Castro, Ahmad Amani, Assensi Oliva, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
non-Newtonian Environment ,Anàlisi numèrica ,Physics ,Non-Newtonian fluids ,Direct numerical simulation ,Mechanics ,Non-Newtonian fluid ,Physics::Fluid Dynamics ,Direct Numerical Simulation (DNS) ,Taylor bubbles ,Bubbles ,Bombolles ,Fluids no newtonians ,Numerical analysis ,Enginyeria mecànica::Mecànica de fluids [Àrees temàtiques de la UPC] - Abstract
Three-dimensional numerical simulation of Taylor gas bubbles as primary unites of slug flow patterns rising in non-Newtonian environments is performed in the context of Direct Numerical Simulation (DNS) of the governing equations, where the whole physics of fluid motions will be taken into account. State-of-the-art numerical tools are proposed to tackle the numerical challenges in the DNS study of this problem. E.g. a coupled level-set volume-of-fluid (CLSVOF) interface capturing method is used to solve the topological changes of the interface. Physical formulations are integrated with moving-mesh (MM) technique to decrease the computational cost of 3D simulations and adaptivemesh-refinement (AMR) technique to increase the local accuracy around the interface. The governing equations are solved using High-Performance Computing (HPC) parallel approaches. To the best of the authors’ knowledge, this is the first work dealing with three-dimensional direct numerical simulation of Taylor bubbles rising in non-Newtonian environments. more...
- Published
- 2021
- Full Text
- View/download PDF
32. Unstructured Level-Set Method For Saturated Liquid-Vapor Phase Change
- Author
-
Néstor Balcázar, Joaquim Rigola, Assensi Oliva, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
Finite element method ,Flux bifàsic ,Materials science ,Level set method ,Flux-Limiters ,Vapor phase ,Analytical chemistry ,Elements finits, Mètode dels ,Física::Termodinàmica [Àrees temàtiques de la UPC] ,Two-phase flow ,Unstructured Meshes ,Finite-Volume Method ,Level set methods ,Vapor-Liquid Phase Change ,Vapor–liquid equilibrium ,Transicions de fase (Física estadística) ,Conservative Level-Set Method ,Corbes de nivell, Mètodes de ,Enginyeria mecànica::Mecànica de fluids [Àrees temàtiques de la UPC] - Abstract
A novel conservative level-set method for saturated liquid-vapor phase change on unstruc-tured meshes is introduced. Transport equations are discretized by the finite-volume method on col-located unstructured grids. Mass transfer promoted by thermal phase change is computed using theenergy jump condition at the interface, as a function of the temperature gradient. The fractional-stepprojection method is used for solving the pressure-velocity coupling, convective terms are discretized byunstructured flux-limiter schemes, central difference scheme is used for discretization of diffusive terms.Verification and validation cases have been undertaken to prove the accuracy and robustness of the nu-merical methods, including simulation of the Stefan problem, and film boiling on a cylindrical surface.Excellent agreement between numerical solutions against analytical solution and empirical correlationsfrom the literature is reported. more...
- Published
- 2021
33. On the feasibility of affordable high-fidelity CFD simulations for indoor environment design and control
- Author
-
Assensi Oliva, R. Capdevila, N. Morozova, Carlos David Pérez-Segarra, F. X. Trias, Universitat Politècnica de Catalunya. Doctorat en Enginyeria Tèrmica, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
Environmental Engineering ,Computer science ,Geography, Planning and Development ,Airflow ,0211 other engineering and technologies ,Indoor air pollution ,02 engineering and technology ,010501 environmental sciences ,Computational fluid dynamics ,01 natural sciences ,High fidelity ,Range (aeronautics) ,Calor -- Convecció ,Mixed convection ,021108 energy ,Simulation ,0105 earth and related environmental sciences ,Civil and Structural Engineering ,Turbulence modeling ,business.industry ,Edificació::Instal·lacions i acondicionament d'edificis [Àrees temàtiques de la UPC] ,Building and Construction ,Dinàmica de fluids computacional ,Turbulència -- Mètodes de simulació ,Heat -- Convection ,Turbulence--Simulation methods ,Cost reduction ,Transient simulations ,Test case ,Natural convection ,Transient (oscillation) ,Real-time simulations ,business ,Enginyeria mecànica::Mecànica de fluids [Àrees temàtiques de la UPC] ,Contaminació de l'ambient interior - Abstract
Computational fluid dynamics (CFD) is a reliable tool for indoor environmental applications. However, accurate CFD simulations require large computational resources, whereas significant cost reduction can lead to unreliable results. The high cost prevents CFD from becoming the primary tool for indoor environmental simulations. Nonetheless, the growth in computational power and advances in numerical algorithms provide an opportunity to use accurate and yet affordable CFD. The objective of this study is to analyze the feasibility of fast, affordable, and high-fidelity CFD simulations for indoor environment design and control using ordinary office computers. We analyze two representative test cases, which imitate common indoor airflow configurations, on a wide range of different turbulence models and discretizations methods, to meet the requirements for the computational cost, run-time, and accuracy. We consider statistically steady-state simulations for indoor environment design and transient simulations for control. Among studied turbulence models, the no-model and large-eddy simulation with staggered discretizations show the best performance. We conclude that high-fidelity CFD simulations on office computers are too slow to be used as a primary tool for indoor environment design and control. Taking into account different laws of computer growth prediction, we estimate the feasibility of high-fidelity CFD on office computers for these applications for the next decades This work is supported by the Ministerio de Economía y Competitividad, Spain [ENE2017-88697-R]. N. Morozova is supported by the by the Ministerio de Economía y Competitividad, Spain [FPU16/06333 predoctoral contract]. Part of the calculations was performed on the MareNostrum 4 supercomputer at the Barcelona Supercomputing Center [RES project I-2019-2-0021]. The authors thankfully acknowledge these institutions. The authors would also like to thank our colleague MSc Xavier Álvarez Farré for the productive discussions. more...
- Published
- 2020
34. Direct numerical simulation of backward-facing step flow at and expansion ratio 2
- Author
-
Assensi Oliva, A. Pont-Vílchez, F. X. Trias, and Andrey Gorobets
- Subjects
Physics ,Turbulence ,Mechanical Engineering ,Direct numerical simulation ,Reynolds number ,Context (language use) ,Inflow ,Mechanics ,Condensed Matter Physics ,01 natural sciences ,010305 fluids & plasmas ,Physics::Fluid Dynamics ,010101 applied mathematics ,symbols.namesake ,Flow (mathematics) ,Mechanics of Materials ,Incompressible flow ,0103 physical sciences ,symbols ,0101 mathematics ,Pressure gradient - Abstract
Backward-facing step (BFS) constitutes a canonical configuration to study wall-bounded flows subject to massive expansions produced by abrupt changes in geometry. Recirculation flow regions are common in this type of flow, driving the separated flow to its downstream reattachment. Consequently, strong adverse pressure gradients arise through this process, feeding flow instabilities. Therefore, both phenomena are strongly correlated as the recirculation bubble shape defines how the flow is expanded, and how the pressure rises. In an incompressible flow, this shape depends on the Reynolds value and the expansion ratio. The influence of these two variables on the bubble length is widely studied, presenting an asymptotic behaviour when both parameters are beyond a certain threshold. This is the usual operating point of many practical applications, such as in aeronautical and environmental engineering. Several numerical and experimental studies have been carried out regarding this topic. The existing simulations considering cases beyond the above-mentioned threshold have only been achieved through turbulence modelling, whereas direct numerical simulations (DNS) have been performed only at low Reynolds numbers. Hence, despite the great importance of achieving this threshold, there is a lack of reliable numerical data to assess the accuracy of turbulence models. In this context, a DNS of an incompressible flow over a BFS is presented in this paper, considering a friction Reynolds number ($Re_{\unicode[STIX]{x1D70F}}$) of 395 at the inflow and an expansion ratio 2. Finally, the elongation of the Kelvin–Helmholtz instabilities along the shear layer is also studied. more...
- Published
- 2019
- Full Text
- View/download PDF
35. A numerical study of liquid atomization regimes by means of conservative level-set simulations
- Author
-
Eugenio Schillaci, Assensi Oliva, Oscar Antepara, Néstor Balcázar, Joaquim Rigola Serrano, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
Work (thermodynamics) ,Conservative level-set ,General Computer Science ,Computer science ,Direct numerical simulation ,Context (language use) ,Computational fluid dynamics ,01 natural sciences ,010305 fluids & plasmas ,Level set ,Two-phase liquid injection ,0103 physical sciences ,0101 mathematics ,Atomització ,Series (mathematics) ,Adaptive mesh refinement ,General Engineering ,Dinàmica de fluids computacional ,Function (mathematics) ,Mechanics ,Solver ,Atomization ,010101 applied mathematics ,Instability and break-up phenomena ,Enginyeria mecànica::Mecànica de fluids [Àrees temàtiques de la UPC] - Abstract
In this work, a conservative level-set finite-volume solver for interface-capturing is employed to perform the direct numerical simulation of Liquid Jets discharging into a quiescent air chamber. The scope is to propose a complete break-up regimes map entirely obtained from numerical simulations. The solver accounts for an adaptive mesh refinement strategy to optimize the computational resources. The numerical model is firstly validated in the context of 3D atomization by simulating the behavior of 3D Coaxial Liquid-Air Jets. Next, we propose an overview of the physical behavior of Liquid Jets, mainly proceeding from theoretical and experimental works. Hence, we perform a series of simulations aimed at studying the variability of the Liquid Jet characteristics as function of selected input parameters. In particular, the analyzed cases are characterized by variable values of Reynolds, Ohnesorge and Weber numbers. The patterns obtained in simulations are compared to the ones expected from bibliographic studies, situating each case on a break-up regime map. A general good agreement is found in the identification of the various break-up regimes and characteristic lengths, while the major differences have been highlighted and interpreted. more...
- Published
- 2019
- Full Text
- View/download PDF
36. Computational investigation of the hexagonal honeycomb adsorption reactor for cooling applications
- Author
-
C. Oliet, Giorgos Papakokkinos, Assensi Oliva, and J. Castro
- Subjects
Materials science ,Adsorption ,Waste heat ,Heat exchanger ,Honeycomb ,Energy Engineering and Power Technology ,Thermodynamics ,Coefficient of performance ,Condenser (heat transfer) ,Industrial and Manufacturing Engineering ,Evaporator ,Fin (extended surface) - Abstract
Adsorption cooling is a sustainable technology, since it can utilize solar energy or waste heat, while employing substances without ozone depletion and global warming potential. The adsorption reactor design is determinant for the system performance. An underexplored geometry hitherto – the hexagonal honeycomb adsorption reactor – was numerically investigated. An in-house, validated, three-dimensional computational model based on unstructured meshes was employed. The Specific Cooling Power (SCP) and Coefficient of Performance (COP) were quantified for several geometrical and operational parameters. The cell inradius creates a dichotomy between SCP and COP, being 218.9 W/kg˙s and 0.356 for 1 mm, while being 80.4 W/kg˙s and 0.606 for 6 mm. The cell height influences prominently the SCP, being 159.5 W/kg˙s and 86.1 W/kg˙s for 5 mm and 30 mm, respectively. The fin thickness impacts mostly the COP, being 0.599 and 0.364 for 0.5 mm and 3 mm, respectively. Higher COP is achieved for higher evaporator, lower adsorption and lower condenser temperatures. Higher SCP is achieved for lower adsorption and condenser, and higher evaporator and desorption temperatures. Shorter cycles result in high SCP and low COP, whereas the inverse occurs for longer cycles. Aluminium heat exchanger yields 7.7% higher COP than copper. The results are discussed from a physical, as well as, an engineering perspective. more...
- Published
- 2022
- Full Text
- View/download PDF
37. Three dimensionality in the wake of the flow around a circular cylinder at Reynolds number 5000
- Author
-
Assensi Oliva, D.E. Aljure, Ivette Rodriguez, O. Lehmkhul, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor, and Universitat Politècnica de Catalunya. TUAREG - Turbulence and Aerodynamics in Mechanical and Aerospace Engineering Research Group more...
- Subjects
Wake three-dimensionality ,Vortex tube ,General Computer Science ,02 engineering and technology ,Starting vortex ,Shear layer ,Vortex shedding ,01 natural sciences ,Reynolds number ,010305 fluids & plasmas ,Physics::Fluid Dynamics ,symbols.namesake ,0203 mechanical engineering ,0103 physical sciences ,Horseshoe vortex ,Fluid mechanics ,Remolins (Mecànica de fluids) ,Physics ,General Engineering ,Mechanics ,Vortex dislocations ,Mecànica de fluids -- Models matemàtics ,Vortex ring ,Vortex ,Coherent structures ,020303 mechanical engineering & transports ,Classical mechanics ,symbols ,Strouhal number ,Burgers vortex ,Direct numerical simulation ,Enginyeria mecànica::Mecànica de fluids [Àrees temàtiques de la UPC] - Abstract
The turbulent flow around a circular cylinder has been investigated at R e = 5000 using direct numerical simulations. Low frequency behavior, vortex undulation, vortex splitting, vortex dislocations and three dimensional flow within the wake were found to happen at this flow regime. In order to successfully capture the wake three dimensionality, different span-wise lengths were considered. It was found that a length L Z = 2 π D was enough to capture this behavior, correctly predicting different aspects of the flow such as drag coefficient, Strouhal number and pressure and velocity distributions when compared to experimental values. Two instability mechanisms were found to coexist in the present case study: a global type instability originating in the shear layer, which shows a characteristic frequency, and a convective type instability that seems to be constantly present in the near wake. Characteristics of both types of instabilities are identified and discussed in detail. As suggested by Norberg, a resonance-type effect takes place in the vortex formation region, as the coexistence of both instability mechanisms result in distorted vortex tubes. However, vortex coherence is never lost within the wake. more...
- Published
- 2017
- Full Text
- View/download PDF
38. DNS of Unequal Size Droplets Collision Using a Moving-Mesh/Level-Set Method
- Author
-
Néstor Balcázar, Assensi Oliva, E. Gutiérrez, Ahmad Amani, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
Level set method ,Materials science ,Turbine blade ,Field (physics) ,DNS ,Binary number ,Spray coating ,Dinàmica de fluids computacional ,Mechanics ,Computational fluid dynamics ,Combustion ,Collision ,Moving Meshes ,law.invention ,law ,Level set methods ,Fluid dynamics ,Corbes de nivell, Mètodes de ,Conservative level set ,Droplets ,Enginyeria mecànica::Mecànica de fluids [Àrees temàtiques de la UPC] - Abstract
The dynamics of binary droplets collision is of huge importance in different fields, from multiphase reactors (Dudukovic et al in Chem Eng Sci 54:1975–1995, 1999 [11]), raindrop formation, ink-jet printing, spray combustion, emulsion stability, turbine blade cooling, spray coating (Ashgriz and Poo in J Fluid Mech 221:183–204, 1990 [5]), and to drug delivery. Due to the complexity of the nature of droplets collision, this topic is one of the most challenging areas in the field of fluid dynamics. We acknowledge Ministerio de Economía y Competitividad, Secretaría de Estado de Investigación, Desarrollo e Innovación, Spain (ENE2017-88697-R). A. Amani acknowledges the financial support of (AGAUR) of Generalitat de Catalunya research scholarship (2016 FI_B 01059). N. Balcázar acknowledges the Programa Torres Quevedo MINECO (PTQ-14-07186). more...
- Published
- 2020
- Full Text
- View/download PDF
39. Improving DES Capabilities for Predicting Kelvin–Helmholtz Instabilities. Comparison with a Backward-Facing Step DNS
- Author
-
Assensi Oliva, Alistair Revell, F. X. Trias, A. Pont-Vílchez, A. P. Duben, Universitat Politècnica de Catalunya. Doctorat en Enginyeria Tèrmica, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
Physics ,Turbulence -- Simulation method ,Turbulence ,Separation (aeronautics) ,Mechanics ,Computational fluid dynamics ,Dinàmica de fluids -- Simulació numérica ,symbols.namesake ,Turbulència -- Simulació numèrica ,Flow (mathematics) ,Helmholtz free energy ,symbols ,Detached eddy simulation ,Reynolds-averaged Navier–Stokes equations ,Enginyeria mecànica::Mecànica de fluids [Àrees temàtiques de la UPC] - Abstract
The Detached Eddy Simulation (DES) turbulence model presented by Spalart et al. (Comments on the Feasibility of LES for Wings, and on a Hybrid RANS/LES Approach, [1]) in the late 90s, was specifically designed to simulate those flow configurations where massive separation was involved more...
- Published
- 2020
- Full Text
- View/download PDF
40. On a Proper Tensor-Diffusivity Model for Large-Eddy Simulations of Buoyancy-Driven Flows
- Author
-
F. Dabbagh, Andrey Gorobets, F. X. Trias, and Assensi Oliva
- Subjects
Physics::Fluid Dynamics ,Physics ,Convection ,Nonlinear system ,Filter (large eddy simulation) ,Work (thermodynamics) ,Heat flux ,Turbulence ,Tensor ,Mechanics ,Thermal diffusivity ,Computer Science::Databases - Abstract
In this work, we plan to shed light on the following research question: can we find a nonlinear subgrid-scale (SGS) heat flux model with good physical and numerical properties, such that we can obtain satisfactory predictions for buoyancy-driven turbulent flows? This is motivated by our findings showing that the classical (linear) eddy-diffusivity assumption fails to provide a reasonable approximation for the SGS heat flux. This was shown in our work [1] where SGS features have been studied a priori for a Rayleigh–Benard convection (RBC). We also concluded that nonlinear (or tensorial) models can give good approximations of the actual SGS heat flux. Briefly, the large-eddy simulation (LES) equations arise from applying a spatial commutative filter, with filter length \(\delta \), to the incompressible Navier–Stokes and thermal energy equations. more...
- Published
- 2020
- Full Text
- View/download PDF
41. Flow topology dynamics in a three-dimensional phase space for turbulent Rayleigh-Bénard convection
- Author
-
Assensi Oliva, F. X. Trias, F. Dabbagh, Andrey Gorobets, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
Fluid Flow and Transfer Processes ,Engineering ,business.industry ,Turbulence ,Computational Mechanics ,Física::Termodinàmica [Àrees temàtiques de la UPC] ,Supercomputer ,Capa límit (Dinàmica de fluids) ,Boundary layer ,Flow (mathematics) ,Fluid dynamics ,Modeling and Simulation ,Phase space ,Dinàmica de fluids ,Christian ministry ,Center (algebra and category theory) ,Aerospace engineering ,IBM ,business ,Rayleigh–Bénard convection ,Turbulència - Abstract
F.X.T., F.D. and A.O. are financially supported by the Ministerio de Economía y Competitividad, Spain (ENE2017-88697-R). F.X.T. is supported by a Ramón y Cajal postdoctoral contract (RYC-2012-11996). F.D. is supported by the Austrian Federal Ministry for Digital and Economic Affairs, the National Foundation for Research, Technology and Development, and the K1MET center for metallurgical research in Austria (www.k1-met.com). Calculations have been performed on the IBM MareNostrum 4 supercomputer at the BSC (PRACE 15th Call, Ref. 2016163972, \Exploring new frontiers in Rayleigh-Bénard convection"). Preliminary simulations were carried out using computational resources of MCC NRC \Kurchatov Institute", http://computing.nrcki.ru/. The authors thankfully acknowledge these institutions. more...
- Published
- 2020
42. DNS of Drag-Force and Reactive Mass Transfer in Gravity-Driven Bubbly Flows
- Author
-
Joaquim Rigola, Assensi Oliva, Néstor Balcázar, Oscar Antepara, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor, and Universitat Politècnica de Catalunya. Doctorat en Enginyeria Tèrmica more...
- Subjects
Physics ,Gravity (chemistry) ,Bubbly Flows ,Unstructured Flux Limiters ,Bubble ,education ,Separation (aeronautics) ,Bubbles--Dynamics ,Multiphase Flow ,Mechanics ,Unstructured Meshes ,Finite-Volume Method ,Physics::Fluid Dynamics ,Drag ,Mass transfer ,Bubbles ,Bombolles ,Navier-Stokes equations ,Transferència de massa ,Equacions de Navier-Stokes ,Bombolles -- Dinàmica ,Unstructured conservative level-set ,Enginyeria mecànica::Mecànica de fluids [Àrees temàtiques de la UPC] - Abstract
Mass transfer processes in bubbly flows are relevant in both nature and industry. Multiple examples arise from the so-called unit operations of the chemical engineering, where bubble columns are used for separation processes, or as chemical and biochemical reactors. In this context, the main motivation of this research is to compute drag-force coefficients and mass transfer coefficients in gravity-driven bubbly flows, using direct numerical simulation of Navier–Stokes equations with a conservative level-set (CLS) [2, 15] methodology for interface capturing in bubble swarms. This work has been financially supported by MINECO (ENE2015-70672-P), and by Termo Fluids S.L., Spain. Néstor Balcázar acknowledges financial support of the Programa Torres Quevedo MINECO (PTQ-14-07186), Spain. Simulations were executed using computing time awarded by PRACE 14th-Call (project 2016153612), and RES (projects F I − 2019 − 1 − 0039 and I M − 2019 − 2 − 0014), on the supercomputer MareNostrum IV based in Barcelona, Spain. more...
- Published
- 2020
- Full Text
- View/download PDF
43. Assessment and Comparison of a Recent Kinematic Sensitive Subgrid Length Scale in Hybrid RANS-LES
- Author
-
F. X. Trias, Alistair Revell, Assensi Oliva, and A. Pont-Vílchez
- Subjects
Physics::Fluid Dynamics ,Physics ,Length scale ,Shear layer ,Homogeneous isotropic turbulence ,Mathematical analysis ,Resilience (materials science) ,Kinematics ,Reynolds-averaged Navier–Stokes equations ,Omega - Abstract
A recent kinematic sensitive subgrid length scale, \(\varDelta _{lsq}\), initially developed for LES applications, is now considered for DES. Even though it is presented as a subgrid length scale, instead of a grey area mitigation (GAM) technique, this initial study shows how it could also be a good and natural approach for addressing this well-known DES shortcoming. In this paper, the \(\varDelta _{lsq}\) has been compared with a well-known kinematic sensitive length scale, \({\tilde{\varDelta }_{\omega }}\). It includes a mesh resilience and a shear layer delay study with a Decaying Homogeneous Isotropic Turbulence configuration and two Backward Facing Step configurations, respectively. Encouraging results have been obtained, indicating \(\varDelta _{lsq}\) as a subgrid length scale to be considered. more...
- Published
- 2019
- Full Text
- View/download PDF
44. Numerical study of binary droplets collision in the main collision regimes
- Author
-
Néstor Balcázar, Assensi Oliva, E. Gutiérrez, Ahmad Amani, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
Materials science ,Conservative level-set ,General Chemical Engineering ,Direct numerical simulation ,Binary number ,02 engineering and technology ,Computational fluid dynamics ,010402 general chemistry ,Kinetic energy ,01 natural sciences ,Energy analysis ,Dinàmica de fluids -- Simulació numérica ,Industrial and Manufacturing Engineering ,Lamella stabilization ,Surface tension ,Physics::Fluid Dynamics ,Environmental Chemistry ,Coalescence (physics) ,General Chemistry ,Mechanics ,Dissipation ,021001 nanoscience & nanotechnology ,Collision ,Energy budget ,0104 chemical sciences ,Comprehensive droplets collision regimes ,0210 nano-technology ,Enginyeria mecànica::Mecànica de fluids [Àrees temàtiques de la UPC] - Abstract
Direct numerical simulation of binary droplets collision is done using a conservative level-set method. The Navier-Stokes and level-set equations are solved using a finite-volume method on collocated grids. A novel lamella stabilization approach is introduced to numerically resolve the thin lamella film appeared during a broad range of collision regimes. This direction-independent method proves to be numerically efficient and accurate compared with experimental data. When the droplets collide, the fluid between them is pushed outward, leaving a thin gas layer bounded by the surface of two droplets. This layer progressively gets thinner and depending on the collision regime, may rupture resulting in coalescence of the droplets or may linger resulting in bouncing-off the droplets. Embedded ghost-nodes layer makes it possible to mimic both bouncing and coalescence phenomena of the droplets collision. The numerical tools introduced are validated and verified against different experimental results for a wide range of collision regimes. A very good agreement is observed between the results of this paper and experimental data available in the literature. A detailed study of the energy budget for different shares of kinetic and dissipation energies inside of the droplet and matrix, in addition to the surface tension energy for studied cases, is provided. Supplementary quantitative values of viscous dissipation rate inside of the matrix and droplet, and also the radial expansion of the droplet are presented as well. more...
- Published
- 2019
45. A second-order time accurate semi-implicit method for fluid–structure interaction problems
- Author
-
Ahmad Amani, Carlos David Pérez-Segarra, Alireza Naseri, Assensi Oliva, I. González, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
Coupling ,Fluid-Structure Interaction ,Partitioned Method ,Mechanical Engineering ,Semi-ImplicitCoupling ,Structure (category theory) ,02 engineering and technology ,Mechanics ,01 natural sciences ,Second-Order Temporal Accuracy ,010305 fluids & plasmas ,Physics::Fluid Dynamics ,Nonlinear system ,020303 mechanical engineering & transports ,Enginyeria mecànica [Àrees temàtiques de la UPC] ,0203 mechanical engineering ,Flow velocity ,0103 physical sciences ,Fluid–structure interaction ,Projection method ,Boundary value problem ,Interacció fluid-estructura ,Displacement (fluid) ,Mathematics ,Projection Method - Abstract
This paper is concerned with numerical solution of fluid-structure inter-action (FSI) problems involving an incompressible viscous flow and an elasticstructure. A semi-implicit partitioned method with second-order temporalaccuracy is proposed. The method separates the pressure term of the fluidequations and strongly couples it to the structure, while the remaining fluidterms and the geometrical nonlinearities are treated explicitly. A second-order projection method is used to solve the fluid equations and also as aframework for the FSI coupling. Particular attention is paid to the boundaryconditions for fluid equations and the accuracy of the fluid pressure on thecommon interface. The proposed coupling method retains the second-orderaccuracy for fully-coupled nonlinear FSI problems. Extensive numerical testsare carried out on a number of benchmark FSI problems and the second-ordertemporal accuracy for all the variables of interest (fluid velocity and pressure,and structural displacement) is demonstrated. more...
- Published
- 2019
46. Numerical analysis of conservative unstructured discretisations for low Mach flows
- Author
-
Assensi Oliva, J. Muela, Carlos David Pérez-Segarra, Oriol Lehmkuhl, J. Ventosa-Molina, and J. Chiva
- Subjects
Mathematical optimization ,Applied Mathematics ,Mechanical Engineering ,Numerical analysis ,Computation ,Computational Mechanics ,Laminar flow ,010103 numerical & computational mathematics ,01 natural sciences ,Least squares ,Computer Science Applications ,010101 applied mathematics ,symbols.namesake ,Mach number ,Mechanics of Materials ,Compressibility ,symbols ,Applied mathematics ,Polygon mesh ,0101 mathematics ,Interpolation ,Mathematics - Abstract
Summary Unstructured meshes allow easily representing complex geometries and to refine in regions of interest without adding control volumes in unnecessary regions. However, numerical schemes used on unstructured grids have to be properly defined in order to minimise numerical errors. An assessment of a low-Mach algorithm for laminar and turbulent flows on unstructured meshes using collocated and staggered formulations is presented. For staggered formulations using cell centred velocity reconstructions the standard first-order method is shown to be inaccurate in low Mach flows on unstructured grids. A recently proposed least squares procedure for incompressible flows is extended to the low Mach regime and shown to significantly improve the behaviour of the algorithm. Regarding collocated discretisations, the odd-even pressure decoupling is handled through a kinetic energy conserving flux interpolation scheme. This approach is shown to efficiently handle variable-density flows. Besides, different face interpolations schemes for unstructured meshes are analysed. A kinetic energy preserving scheme is applied to the momentum equations, namely the Symmetry-Preserving (SP) scheme. Furthermore, a new approach to define the far-neighbouring nodes of the QUICK scheme is presented and analysed. The method is suitable for both structured and unstructured grids, either uniform or not. The proposed algorithm and the spatial schemes are assessed against a function reconstruction, a differentially heated cavity and a turbulent self-igniting diffusion flame. It is shown that the proposed algorithm accurately represents unsteady variable-density flows. Furthermore, the QUICK schemes shows close to second order behaviour on unstructured meshes and the SP is reliably used in all computations. This article is protected by copyright. All rights reserved. VAPFLOW - Analysis of mass transfer and phase change phenomena in moist air environments: frosting, defrosting and supersaturated stream mixing' of the Spanish Government VAPFLOW; contract/grant number: ENE2012-36910 more...
- Published
- 2016
- Full Text
- View/download PDF
47. Numerical and experimental investigation of a vertical LiBr falling film absorber considering wave regimes and in presence of mist flow
- Author
-
J. Castro, E. García-Rivera, J. Farnós, Assensi Oliva, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
Heat--Transmission ,Materials science ,Evaporació ,020209 energy ,Evaporation ,02 engineering and technology ,Energies::Tecnologia energètica [Àrees temàtiques de la UPC] ,Absorption ,Vertical falling film ,Experimental ,Optics ,Fluid dynamics ,020401 chemical engineering ,Deflection (engineering) ,Mass transfer ,0202 electrical engineering, electronic engineering, information engineering ,0204 chemical engineering ,Wavy regime ,LiBr ,Numerical ,Mathematical model ,business.industry ,General Engineering ,Mist ,Experimental data ,Mechanics ,Condensed Matter Physics ,Drag ,Dinàmica de fluids ,Free surface ,Calor--Transmissió ,Transferència de massa ,business ,Water vapor ,Enginyeria mecànica::Mecànica de fluids [Àrees temàtiques de la UPC] - Abstract
The absorber represents the most critical component in absorption systems and one of the key issues. In this component complex heat and mass transfer phenomena during the absorption process takes place simultaneously. For this reason the development of mathematical models validated against experimental data always constitutes useful tools for the design and improvement of falling film absorbers. A testing device has been designed and built to reproduce absorption phenomena in vertical LiBr − H 2 O falling film absorbers with the primary objective to obtain experimental data. On the other hand, a mathematical model of falling film absorption of H 2 O vapour in LiBr aqueous solutions has been implemented. Wave regime is considered by including and solving the Free Surface Deflection Equation. The numerical results are validated using the experimental data. During the development of this work, the authors have paid careful attention to the verification of experimental data. Such verification consists of performing energy and mass balances in the fluid film side. Important discrepancies were found in our experimental data. Therefore, an extensive study was carried out in order to find the source of such errors. The conclusion is that there is a drag of LiBr solution in the water vapour which increases with the Re number. This mist flow cannot be measured experimentally, but can be evaluated in an indirect way. The mathematical models have been adapted in order to consider the influence of mist flow. On the other hand, in the literature there are not many experimental works related to falling film absorbers which expose enough information to verify the reliability of their experimental data. more...
- Published
- 2016
- Full Text
- View/download PDF
48. Drain water heat recovery storage-type unit for residential housing
- Author
-
Assensi Oliva, Joaquim Rigola, C. Oliet, S. Torras, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
Work (thermodynamics) ,Sensible heat storage ,020209 energy ,Energy Engineering and Power Technology ,02 engineering and technology ,010501 environmental sciences ,Computational fluid dynamics ,Accumulation water tank ,Thermal energy storage ,01 natural sciences ,Industrial and Manufacturing Engineering ,Waste heat recovery unit ,Drain water ,Habitatges--Estalvi d'energia ,Experimental ,Heat recovery ventilation ,Waste heat ,0202 electrical engineering, electronic engineering, information engineering ,Heat storage ,Energies::Eficiència energètica::Eficiència domèstica [Àrees temàtiques de la UPC] ,0105 earth and related environmental sciences ,Computer simulation ,Petroleum engineering ,business.industry ,Internal flow ,Calor--Emmagatzematge ,Calor--Recuperació ,Environmental engineering ,Dwellings--Energy conservation ,Heat recovery ,Environmental science ,Energies::Recursos energètics renovables [Àrees temàtiques de la UPC] ,CFD ,business - Abstract
© 2016. This version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ The drain water heat recovery (DWHR) system is an interesting household technology to reduce energy costs and environmental impact. The objective of the utilisation of these devices is the recovery of the waste heat from domestic warm drain water, and transferring it to cold water entering the house. A drain water heat recovery unit has been built in this work. The authors are using both numerical and experimental tools to design and study the performance of this device, focusing on the analysis of a specific drain water heat recovery storage-type based on a cylindrical tank with an internal coiled pipe. The numerical simulation has been performed using an in-house platform, where the different elements of the DWHR storage are linked to solve the system. On the other hand, an experimental infrastructure has been developed to analyse of the system, which has been instrumented to provide detailed information of its heat recovery and storage capacities and temperature map. Different internal flow rates and operational temperatures have been studied. From the results obtained it can be said that the device shows interesting heat recovery and storage capacities, while the numerical platform shows promising comparison results against the experiments. more...
- Published
- 2016
- Full Text
- View/download PDF
49. Flow Over a Realistic Car Model: WMLES Assessment and Turbulent Structures
- Author
-
D.E. Aljure, J. Calafell, Assensi Oliva, and A. Baez
- Subjects
symbols.namesake ,Flow (mathematics) ,Car model ,Turbulence ,symbols ,Reynolds number ,Applied mathematics ,Mathematics - Abstract
Most CFD research on automotive external aerodynamics has been carried out using very simplified models such as the Ahmed car (Aljure, Lehmkuhl, Rodriguez, Oliva, Comput Fluids, 96:122–135, (2014), [1]). To reduce the gap between the production cars and models used for academic purposes, the DrivAer car model was introduced in 2012. References (Heft, Indinger, Adams, SAE Tech Pap, No. 2012-01-0168, (2012), [2], Strangfeld, Wieser, Schmidt, Woszidlo, Nateri, Paschereit, SAE Tech Pap, No. 2013-01-1251, (2013), [3]) performed experimental observations on this geometry. Their results suggested that the Reynolds number dependency of the force coefficients decreased as Re increased. Two values have been reported for Re number independence, \(Re=2\times 10^6\) (Strangfeld, Wieser, Schmidt, Woszidlo, Nateri, Paschereit, SAE Tech Pap, No. 2013-01-1251, (2013), [3]) and \(Re=4.87\times 10^6\) (Heft, Indinger, Adams, SAE Tech Pap, No. 2012-01-0168, (2012), [2]). more...
- Published
- 2019
- Full Text
- View/download PDF
50. Detailed prediction of fluid-solid coupled phenomena of turbulent flow through reed valves
- Author
-
Assensi Oliva, Alireza Naseri, Joaquim Rigola, I. González, Carlos David Pérez-Segarra, Universitat Politècnica de Catalunya. Doctorat en Enginyeria Tèrmica, Universitat Politècnica de Catalunya. Departament de Màquines i Motors Tèrmics, and Universitat Politècnica de Catalunya. CTTC - Centre Tecnològic de la Transferència de Calor more...
- Subjects
Pressure drop ,Suction ,Reciprocating compressor ,Turbulence ,Numerical analysis ,Vàlvules ,Mechanics ,Valves ,Turbulence--Simulation methods ,Physics::Fluid Dynamics ,Turbulència -- Simulació numèrica ,Normal mode ,Penalty method ,Geology ,Large eddy simulation ,Enginyeria mecànica::Mecànica de fluids [Àrees temàtiques de la UPC] - Abstract
The operation of self-actuated valves in suction and discharge processes plays a crucial role in the thermal efficiency and structural reliability of hermetic reciprocating compressors. The present work provides a thorough description of an in-house numerical method based on a partitioned fluid-structure interaction algorithm intended to obtain high-fidelity numerical predictions and optimise valve system design. A large eddy simulation model is used for the turbulent flow, whereas a normal mode superposition assumption along with an impact penalty method is used for the reed. Under this framework, a detailed analysis of the coupled problem with a straight and tapered exit ports is carried out. Differences in effective flow area and pressure drop are found as a result of the port geometry, but also of the valve velocity. more...
- Published
- 2019
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.