CTTC - Centre Tecnològic de la Transferència de Calor
http://hdl.handle.net/2117/3190
Sat, 24 Jul 2021 02:12:25 GMT2021-07-24T02:12:25ZOptimization of the progress variable definition using a genetic algorithm for the combustion of complex fuels
http://hdl.handle.net/2117/350010
Optimization of the progress variable definition using a genetic algorithm for the combustion of complex fuels
Both, Ambrus; Mira Martínez, Daniel; Lehmkuhl Barba, Oriol
In this work counterflow diffusion flamelets of n-heptane and air are used at stable and unsteady extinguishing conditions for building a thermo-chemical database for Computational Fluid Dynamics (CFD) calculations. The injectivity of the progress variable definition is achieved through an optimization process using a genetic algorithm in combination with an adequate objective function.
Fri, 23 Jul 2021 10:24:25 GMThttp://hdl.handle.net/2117/3500102021-07-23T10:24:25ZBoth, AmbrusMira Martínez, DanielLehmkuhl Barba, OriolIn this work counterflow diffusion flamelets of n-heptane and air are used at stable and unsteady extinguishing conditions for building a thermo-chemical database for Computational Fluid Dynamics (CFD) calculations. The injectivity of the progress variable definition is achieved through an optimization process using a genetic algorithm in combination with an adequate objective function.High-fidelity simulations of the mixing and combustion of a technically premixed hydrogen flame
http://hdl.handle.net/2117/350008
High-fidelity simulations of the mixing and combustion of a technically premixed hydrogen flame
Mira Martínez, Daniel; Both, Ambrus; Lehmkuhl Barba, Oriol; Gomez Gonzalez, Samuel; Forck, Jonathan; Tanneberger, Tom; Stathopoulos, Panagiotis; Paschereit, Christian Oliver
Numerical simulations are used here to obtain further understanding on the flashback mechanism of a technically premixed hydrogen flame operated in lean conditions. Recent work from the authors (Mira et al., 2020) showed that the hydrogen momentum strongly influences the flame dynamics and plays a fundamental role on the stability limits of the combustor. The axial injection influences the vortex breakdown position and therefore, the propensity of the burner to produce flashback. This work is an extension of our previous work where we include a detailed description of the mixing process and the influence of equivalence ratio fluctuations and heat loss on the flame dynamics.
Fri, 23 Jul 2021 10:16:58 GMThttp://hdl.handle.net/2117/3500082021-07-23T10:16:58ZMira Martínez, DanielBoth, AmbrusLehmkuhl Barba, OriolGomez Gonzalez, SamuelForck, JonathanTanneberger, TomStathopoulos, PanagiotisPaschereit, Christian OliverNumerical simulations are used here to obtain further understanding on the flashback mechanism of a technically premixed hydrogen flame operated in lean conditions. Recent work from the authors (Mira et al., 2020) showed that the hydrogen momentum strongly influences the flame dynamics and plays a fundamental role on the stability limits of the combustor. The axial injection influences the vortex breakdown position and therefore, the propensity of the burner to produce flashback. This work is an extension of our previous work where we include a detailed description of the mixing process and the influence of equivalence ratio fluctuations and heat loss on the flame dynamics.Energy preserving multiphase flows: applications to falling films
http://hdl.handle.net/2117/348859
Energy preserving multiphase flows: applications to falling films
Valle Marchante, Nicolás; Trias Miquel, Francesc Xavier; Castro González, Jesús
The numerical simulation of multiphase flows presents several challenges, namely the transport of different phases within de domain and the inclusion of capillary effects. Here, these are approached by enforcing a discrete physics-compatible solution. Extending our previous work on the discretization of surface tension [N. Valle, F. X. Trias, and J. Castro, 'An energy-preserving level set method for multiphase flows,' J. Comput. Phys., vol. 400, p. 108991, 2020] with a consistent mass and momentum transfer a fully energy-preserving multiphase flow method is presented. This numerical technique is showcased within the simulation of a falling film under several working conditions related to the normal operation of LiBr absorption chillers.
Fri, 09 Jul 2021 08:33:22 GMThttp://hdl.handle.net/2117/3488592021-07-09T08:33:22ZValle Marchante, NicolásTrias Miquel, Francesc XavierCastro González, JesúsThe numerical simulation of multiphase flows presents several challenges, namely the transport of different phases within de domain and the inclusion of capillary effects. Here, these are approached by enforcing a discrete physics-compatible solution. Extending our previous work on the discretization of surface tension [N. Valle, F. X. Trias, and J. Castro, 'An energy-preserving level set method for multiphase flows,' J. Comput. Phys., vol. 400, p. 108991, 2020] with a consistent mass and momentum transfer a fully energy-preserving multiphase flow method is presented. This numerical technique is showcased within the simulation of a falling film under several working conditions related to the normal operation of LiBr absorption chillers.Development of a reduced order model of solar heat gains prediction
http://hdl.handle.net/2117/345273
Development of a reduced order model of solar heat gains prediction
Tamm, Meril; Macià, Jordi; Capdevila Paramio, Roser; Farnós Baulenas, Joan; Thalfeldt, Martin; Kurnitski, Jarek
The aim of this study was to elaborate and validate a reduced order model able to forecast solar heat gains as a function of the architectural parameters that determine the solar heat gains. The study focused on office buildings in Catalonia and Spain and their physical values were taken from the Spanish Building Technical Code and European Union Directive 2018/844. A reduced order model with three direct variables (solar heat gain coefficient, shade factor, window to wall ratio) and one indirect design variable (building orientation) was obtained and validated in respect to the International Performance Measurement and Verification Protocol. Building envelope properties were fixed and the values were taken from the national standards of Spain. This work validates solar heat gain coefficient as a primary variable in determining the annual solar heat gains in a building. Further work of developed model could result in building energy need quick evaluation tool in terms of solar heat gains for architects in building early stage as it has an advantage over detailed building simulation programs in terms of instant calculation and the limited need for predefined input data.
Fri, 07 May 2021 07:56:02 GMThttp://hdl.handle.net/2117/3452732021-05-07T07:56:02ZTamm, MerilMacià, JordiCapdevila Paramio, RoserFarnós Baulenas, JoanThalfeldt, MartinKurnitski, JarekThe aim of this study was to elaborate and validate a reduced order model able to forecast solar heat gains as a function of the architectural parameters that determine the solar heat gains. The study focused on office buildings in Catalonia and Spain and their physical values were taken from the Spanish Building Technical Code and European Union Directive 2018/844. A reduced order model with three direct variables (solar heat gain coefficient, shade factor, window to wall ratio) and one indirect design variable (building orientation) was obtained and validated in respect to the International Performance Measurement and Verification Protocol. Building envelope properties were fixed and the values were taken from the national standards of Spain. This work validates solar heat gain coefficient as a primary variable in determining the annual solar heat gains in a building. Further work of developed model could result in building energy need quick evaluation tool in terms of solar heat gains for architects in building early stage as it has an advantage over detailed building simulation programs in terms of instant calculation and the limited need for predefined input data.A comprehensive simulation tool for adsorption-based solar-cooled buildings. Control strategy based on variable cycle duration
http://hdl.handle.net/2117/335766
A comprehensive simulation tool for adsorption-based solar-cooled buildings. Control strategy based on variable cycle duration
Papakokkinos, Giorgos; Castro González, Jesús; Capdevila Paramio, Roser; Damble, Rashmin
Adsorption cooling systems (ACS) may contribute towards a sustainable way of satisfying the increasing cooling demand, as they utilize solar thermal energy and employ non-ozone-depleting substances. Apart from the intrinsic ACS performance, the successfulness of its operation depends on its integration within the entire thermal system (solar collectors, thermal storage and building), which is not straight-forward due to thermal inertia effects and its inherent cyclic operation. Numerical simulations can contribute in understanding the system behavior, its adequate dimensioning and the implementation of optimized control strategies. A computational model was developed, capable of performing conjugate, dynamic simulations of the entire thermal system. The influence of the control criteria is investigated and quantified through three simulation phases, conducted for various solar collectors areas and storage volumes. Higher solar fraction is achieved for lower auxiliary heater activation temperature and lower temperature difference activation of the solar pump. Subsequently, simulations with variable cycle duration were performed, using optimized cycle duration according to the instantaneous operating temperatures. This approach reduces significantly the auxiliary consumption or satifies the demand with less solar collectors. The potential CO2 emissions avoidance is calculated between 28.1-90.7% with respect to four scenarios of electricity-driven systems of different performance and CO2 emission intensity.
Thu, 21 Jan 2021 17:54:36 GMThttp://hdl.handle.net/2117/3357662021-01-21T17:54:36ZPapakokkinos, GiorgosCastro González, JesúsCapdevila Paramio, RoserDamble, RashminAdsorption cooling systems (ACS) may contribute towards a sustainable way of satisfying the increasing cooling demand, as they utilize solar thermal energy and employ non-ozone-depleting substances. Apart from the intrinsic ACS performance, the successfulness of its operation depends on its integration within the entire thermal system (solar collectors, thermal storage and building), which is not straight-forward due to thermal inertia effects and its inherent cyclic operation. Numerical simulations can contribute in understanding the system behavior, its adequate dimensioning and the implementation of optimized control strategies. A computational model was developed, capable of performing conjugate, dynamic simulations of the entire thermal system. The influence of the control criteria is investigated and quantified through three simulation phases, conducted for various solar collectors areas and storage volumes. Higher solar fraction is achieved for lower auxiliary heater activation temperature and lower temperature difference activation of the solar pump. Subsequently, simulations with variable cycle duration were performed, using optimized cycle duration according to the instantaneous operating temperatures. This approach reduces significantly the auxiliary consumption or satifies the demand with less solar collectors. The potential CO2 emissions avoidance is calculated between 28.1-90.7% with respect to four scenarios of electricity-driven systems of different performance and CO2 emission intensity.A scalable framework for the partitioned solution of fluid-structure interaction problems
http://hdl.handle.net/2117/335760
A scalable framework for the partitioned solution of fluid-structure interaction problems
Naseri, Alireza; Totounferoush, Amin; González Acedo, Ignacio; Mehl, Miriam; Pérez Segarra, Carlos David
In this work, we present a scalable and efficient parallel solver for the partitioned solution of fluid–structure interaction problems through multi-code coupling. Two instances of an in-house parallel software, TermoFluids, are used to solve the fluid and the structural sub-problems, coupled together on the interface via the preCICE coupling library. For fluid flow, the Arbitrary Lagrangian–Eulerian form of the Navier–Stokes equations is solved on an unstructured conforming grid using a second-order finite-volume discretization. A parallel dynamic mesh method for unstructured meshes is used to track the moving boundary. For the structural problem, the nonlinear elastodynamics equations are solved on an unstructured grid using a second-order finite-volume method. A semi-implicit FSI coupling method is used which segregates the fluid pressure term and couples it strongly to the structure, while the remaining fluid terms and the geometrical nonlinearities are only loosely coupled. A robust and advanced multi-vector quasi-Newton method is used for the coupling iterations between the solvers. Both the fluid and the structural solver use distributed-memory parallelism. The intra-solver communication required for data update in the solution process is carried out using non-blocking point-to-point communicators. The inter-code communication is fully parallel and point-to-point, avoiding any central communication unit. Inside each single-physics solver, the load is balanced by dividing the computational domain into fairly equal blocks for each process. Additionally, a load balancing model is used at the inter-code level to minimize the overall idle time of the processes. Two practical test cases in the context of hemodynamics are studied, demonstrating the accuracy and computational efficiency of the coupled solver. Strong scalability test results show a parallel efficiency of 83% on 10,080 CPU cores.
Thu, 21 Jan 2021 15:41:53 GMThttp://hdl.handle.net/2117/3357602021-01-21T15:41:53ZNaseri, AlirezaTotounferoush, AminGonzález Acedo, IgnacioMehl, MiriamPérez Segarra, Carlos DavidIn this work, we present a scalable and efficient parallel solver for the partitioned solution of fluid–structure interaction problems through multi-code coupling. Two instances of an in-house parallel software, TermoFluids, are used to solve the fluid and the structural sub-problems, coupled together on the interface via the preCICE coupling library. For fluid flow, the Arbitrary Lagrangian–Eulerian form of the Navier–Stokes equations is solved on an unstructured conforming grid using a second-order finite-volume discretization. A parallel dynamic mesh method for unstructured meshes is used to track the moving boundary. For the structural problem, the nonlinear elastodynamics equations are solved on an unstructured grid using a second-order finite-volume method. A semi-implicit FSI coupling method is used which segregates the fluid pressure term and couples it strongly to the structure, while the remaining fluid terms and the geometrical nonlinearities are only loosely coupled. A robust and advanced multi-vector quasi-Newton method is used for the coupling iterations between the solvers. Both the fluid and the structural solver use distributed-memory parallelism. The intra-solver communication required for data update in the solution process is carried out using non-blocking point-to-point communicators. The inter-code communication is fully parallel and point-to-point, avoiding any central communication unit. Inside each single-physics solver, the load is balanced by dividing the computational domain into fairly equal blocks for each process. Additionally, a load balancing model is used at the inter-code level to minimize the overall idle time of the processes. Two practical test cases in the context of hemodynamics are studied, demonstrating the accuracy and computational efficiency of the coupled solver. Strong scalability test results show a parallel efficiency of 83% on 10,080 CPU cores.On the feasibility of affordable high-fidelity CFD simulations for indoor environment design and control
http://hdl.handle.net/2117/335584
On the feasibility of affordable high-fidelity CFD simulations for indoor environment design and control
Morozova, Nina; Trias Miquel, Francesc Xavier; Capdevila Paramio, Roser; Pérez Segarra, Carlos David; Oliva Llena, Asensio
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
Tue, 19 Jan 2021 18:53:57 GMThttp://hdl.handle.net/2117/3355842021-01-19T18:53:57ZMorozova, NinaTrias Miquel, Francesc XavierCapdevila Paramio, RoserPérez Segarra, Carlos DavidOliva Llena, AsensioComputational 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 decadesA hierarchical parallel implementation for heterogeneous computing. Application to algebra-based CFD simulations on hybrid supercomputers
http://hdl.handle.net/2117/335542
A hierarchical parallel implementation for heterogeneous computing. Application to algebra-based CFD simulations on hybrid supercomputers
Álvarez Farré, Xavier; Gorobets, Andrey; Trias Miquel, Francesc Xavier
The quest for new portable implementations of simulation algorithms is motivated by the increasing variety of computing architectures. Moreover, the hybridization of high-performance computing systems imposes additional constraints, since heterogeneous computations are needed to efficiently engage processors and massively-parallel accelerators. This, in turn, involves different parallel paradigms and computing frameworks and requires complex data exchanges between computing units. Typically, simulation codes rely on sophisticated data structures and computing subroutines, so-called kernels, which makes portability terribly cumbersome. Thus, a natural way to achieve portability is to dramatically reduce the complexity of both data structures and computing kernels. In our algebra-based approach, the scale-resolving simulation of incompressible turbulent flows on unstructured meshes relies on three fundamental kernels: the sparse matrix-vector product, the linear combination of vectors and the dot product. It is noteworthy that this approach is not limited to a particular kind of numerical method or a set of governing equations. In our code, an auto-balanced multilevel partitioning distributes workload among computing devices of various architectures. The overlap of computations and multistage communications efficiently hides the data exchanges overhead in large-scale supercomputer simulations. In addition to computing on accelerators, special attention is paid at efficiency on manycore processors in multiprocessor nodes with significant non-uniform memory access factor. Parallel efficiency and performance are studied in detail for different execution modes on various supercomputers using up to 9,600 processor cores and up to 256 graphics processor units. The heterogeneous implementation model described in this work is a general-purpose approach that is well suited for various subroutines in numerical simulation codes.
Tue, 19 Jan 2021 13:25:50 GMThttp://hdl.handle.net/2117/3355422021-01-19T13:25:50ZÁlvarez Farré, XavierGorobets, AndreyTrias Miquel, Francesc XavierThe quest for new portable implementations of simulation algorithms is motivated by the increasing variety of computing architectures. Moreover, the hybridization of high-performance computing systems imposes additional constraints, since heterogeneous computations are needed to efficiently engage processors and massively-parallel accelerators. This, in turn, involves different parallel paradigms and computing frameworks and requires complex data exchanges between computing units. Typically, simulation codes rely on sophisticated data structures and computing subroutines, so-called kernels, which makes portability terribly cumbersome. Thus, a natural way to achieve portability is to dramatically reduce the complexity of both data structures and computing kernels. In our algebra-based approach, the scale-resolving simulation of incompressible turbulent flows on unstructured meshes relies on three fundamental kernels: the sparse matrix-vector product, the linear combination of vectors and the dot product. It is noteworthy that this approach is not limited to a particular kind of numerical method or a set of governing equations. In our code, an auto-balanced multilevel partitioning distributes workload among computing devices of various architectures. The overlap of computations and multistage communications efficiently hides the data exchanges overhead in large-scale supercomputer simulations. In addition to computing on accelerators, special attention is paid at efficiency on manycore processors in multiprocessor nodes with significant non-uniform memory access factor. Parallel efficiency and performance are studied in detail for different execution modes on various supercomputers using up to 9,600 processor cores and up to 256 graphics processor units. The heterogeneous implementation model described in this work is a general-purpose approach that is well suited for various subroutines in numerical simulation codes.Tetrahedral adaptive mesh refinement for two-phase flows using conservative level-set method
http://hdl.handle.net/2117/335448
Tetrahedral adaptive mesh refinement for two-phase flows using conservative level-set method
Antepara Zambrano, Óscar; Balcázar Arciniega, Néstor; Oliva Llena, Asensio
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.
Mon, 18 Jan 2021 11:11:01 GMThttp://hdl.handle.net/2117/3354482021-01-18T11:11:01ZAntepara Zambrano, ÓscarBalcázar Arciniega, NéstorOliva Llena, AsensioIn 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.Transient model for the development of an air-cooled LiBr-H2O absorption chiller based on heat and mass transfer empirical correlations
http://hdl.handle.net/2117/335434
Transient model for the development of an air-cooled LiBr-H2O absorption chiller based on heat and mass transfer empirical correlations
Castro González, Jesús; Farnós Baulenas, Joan; Papakokkinos, Giorgos; Zheng, Jian; Oliet Casasayas, Carles
This work describes transient numerical modeling of a direct air-cooled,single-effect absorption chiller. The model is lumped parametric based on transient mass, momentum, and energy balances, applied to the internal components of the absorption machine. Thermal and mass storage in each one of the components are taken into account in the transient evaluation, and pressure losses in the SHX are evaluated using a pressure drop coefficient. This work aims to improve the available numerical modeling propositions by using embedded available heat and mass transfer empirical correlations, based on previous experiences in falling film absorption. This approach minimizes the need for experimental parameter identification and allows scalability studies. The experimental validation has been organized in three steps: i) absorber zero-order model, steady-state conditions; ii) the whole chiller, also in steady-state conditions; iii) transient conditions. For the steady-state conditions, most results have an agreement within the margin of the uncertainty of the experiments,with a medium discrepancy of 5% in COP and 11% in the cooling capacity. For transient conditions, the comparison of the outlet temperatures of the secondary streams, reveals discrepancies under 0.5 K, except in some fast transient periods where higher differences are perceived. To perform the numerical simulations isused as an in-house modular object-oriented simulation platform (NEST plat-form). Finally, the performance of a prototype demonstration 7 kW air-cooled LiBr-H2O absorption chiller is predicted through a designed test campaign. This model put gives valuable information for the definition of further regulation and control protocols
Mon, 18 Jan 2021 09:24:44 GMThttp://hdl.handle.net/2117/3354342021-01-18T09:24:44ZCastro González, JesúsFarnós Baulenas, JoanPapakokkinos, GiorgosZheng, JianOliet Casasayas, CarlesThis work describes transient numerical modeling of a direct air-cooled,single-effect absorption chiller. The model is lumped parametric based on transient mass, momentum, and energy balances, applied to the internal components of the absorption machine. Thermal and mass storage in each one of the components are taken into account in the transient evaluation, and pressure losses in the SHX are evaluated using a pressure drop coefficient. This work aims to improve the available numerical modeling propositions by using embedded available heat and mass transfer empirical correlations, based on previous experiences in falling film absorption. This approach minimizes the need for experimental parameter identification and allows scalability studies. The experimental validation has been organized in three steps: i) absorber zero-order model, steady-state conditions; ii) the whole chiller, also in steady-state conditions; iii) transient conditions. For the steady-state conditions, most results have an agreement within the margin of the uncertainty of the experiments,with a medium discrepancy of 5% in COP and 11% in the cooling capacity. For transient conditions, the comparison of the outlet temperatures of the secondary streams, reveals discrepancies under 0.5 K, except in some fast transient periods where higher differences are perceived. To perform the numerical simulations isused as an in-house modular object-oriented simulation platform (NEST plat-form). Finally, the performance of a prototype demonstration 7 kW air-cooled LiBr-H2O absorption chiller is predicted through a designed test campaign. This model put gives valuable information for the definition of further regulation and control protocols