Ponències/Comunicacions de congressos
http://hdl.handle.net/2117/3193
2017-04-29T05:43:27ZNew differential operators and discretization methods for large-eddy simulation and regularization modeling
http://hdl.handle.net/2117/103806
New differential operators and discretization methods for large-eddy simulation and regularization modeling
Trias Miquel, Francesc Xavier; Gorobets, Andrei; Pérez Segarra, Carlos David; Oliva Llena, Asensio
Direct numerical simulations (DNS) of the incompressible Navier-Stokes equations are limited to relatively low-Reynolds numbers. Therefore, dynamically less complex mathematical formulations are necessary for coarse-grain simulations. Regularization and eddy-viscosity models for Large-Eddy Simulation are examples thereof. They rely on differential operators that should be able to capture well different flow configurations (laminar and 2D flows, near-wall behavior, transitional regime...). Most of them are based on the combination of invariants of a symmetric second-order tensor that is derived from the gradient of the resolved velocity field. In the present work, they are presented in a framework where all the models are represented as a combination of elements of a 5D phase space of invariants. In this way, new models can be constructed by imposing appropriate restrictions in this space. Moreover, since the discretization errors may play an important role, a novel approach to discretize the viscous term with spatially varying eddy-viscosity is used. It is based on basic operators; therefore, the implementation is straightforward even for staggered formulations. The performance of the proposed methods will be assessed by means of direct comparison to DNS reference results.
2017-04-27T16:58:27ZTrias Miquel, Francesc XavierGorobets, AndreiPérez Segarra, Carlos DavidOliva Llena, AsensioDirect numerical simulations (DNS) of the incompressible Navier-Stokes equations are limited to relatively low-Reynolds numbers. Therefore, dynamically less complex mathematical formulations are necessary for coarse-grain simulations. Regularization and eddy-viscosity models for Large-Eddy Simulation are examples thereof. They rely on differential operators that should be able to capture well different flow configurations (laminar and 2D flows, near-wall behavior, transitional regime...). Most of them are based on the combination of invariants of a symmetric second-order tensor that is derived from the gradient of the resolved velocity field. In the present work, they are presented in a framework where all the models are represented as a combination of elements of a 5D phase space of invariants. In this way, new models can be constructed by imposing appropriate restrictions in this space. Moreover, since the discretization errors may play an important role, a novel approach to discretize the viscous term with spatially varying eddy-viscosity is used. It is based on basic operators; therefore, the implementation is straightforward even for staggered formulations. The performance of the proposed methods will be assessed by means of direct comparison to DNS reference results.Analysis of IAQ based on modeling of building envelope coupled with CFD&HT room airflow
http://hdl.handle.net/2117/103805
Analysis of IAQ based on modeling of building envelope coupled with CFD&HT room airflow
Capdevila Paramio, Roser; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; López Mas, Joan; Oliva Llena, Asensio
Buildings represent a major part of the world energy requirement. The simulation of combined heat, air and moisture (HAM) and pollutant transfer in this context is important to predict the indoor air quality (IAQ), along with the thermal comfort inside the buildings. Moreover, it is important to have appropriate levels of indoor humidity along with the room temperature as movement of water vapor through the building envelope causes a lot of harm to the building structure and reduces the quality of its thermal insulation leading to higher energy demand. In modern houses people is exposed to a big amount of building materials, many of which release pollutants, many of them are volatile organic compounds (VOCs) that degrade the IAQ. The knowledge of the peak loads, temperatures, humidity levels, pollutant dispersion can help to optimize the design of new buildings or existing buildings that need to be refurbished and therefore results in energy efficient buildings.
In this work a modular object-oriented building simulation tool (NEST) with CFD&HT code Termofluids, capable of coupling different levels of simulation models, allowing the simulation of heat, air, moisture and pollutant distribution (multizone model, envelope model, room analysis and HVAC system) and VOC is presented. The modular approach gives flexibility of choosing a model for each element and to have different levels of modeling for different elements in the system. Special attention has been focused on: the large eddy simulation turbulence models used for the room air dynamics and pollutants distribution transport and high performance parallel software. Parallelization of the building simulation is necessary if some critical processes/zones need to be modeled with more detail for reducing computational time. The main focus of this article is to couple the HAM and pollutants models for the building envelope with CFD&HT models with heat, moisture and pollutant transfer models for room airflow. An analysis of the effect of different materials on the IAQ of the buildings will be performed
2017-04-27T16:44:08ZCapdevila Paramio, RoserLehmkuhl Barba, OriolRigola Serrano, JoaquimLópez Mas, JoanOliva Llena, AsensioBuildings represent a major part of the world energy requirement. The simulation of combined heat, air and moisture (HAM) and pollutant transfer in this context is important to predict the indoor air quality (IAQ), along with the thermal comfort inside the buildings. Moreover, it is important to have appropriate levels of indoor humidity along with the room temperature as movement of water vapor through the building envelope causes a lot of harm to the building structure and reduces the quality of its thermal insulation leading to higher energy demand. In modern houses people is exposed to a big amount of building materials, many of which release pollutants, many of them are volatile organic compounds (VOCs) that degrade the IAQ. The knowledge of the peak loads, temperatures, humidity levels, pollutant dispersion can help to optimize the design of new buildings or existing buildings that need to be refurbished and therefore results in energy efficient buildings.
In this work a modular object-oriented building simulation tool (NEST) with CFD&HT code Termofluids, capable of coupling different levels of simulation models, allowing the simulation of heat, air, moisture and pollutant distribution (multizone model, envelope model, room analysis and HVAC system) and VOC is presented. The modular approach gives flexibility of choosing a model for each element and to have different levels of modeling for different elements in the system. Special attention has been focused on: the large eddy simulation turbulence models used for the room air dynamics and pollutants distribution transport and high performance parallel software. Parallelization of the building simulation is necessary if some critical processes/zones need to be modeled with more detail for reducing computational time. The main focus of this article is to couple the HAM and pollutants models for the building envelope with CFD&HT models with heat, moisture and pollutant transfer models for room airflow. An analysis of the effect of different materials on the IAQ of the buildings will be performedNumerical analysis of suction mufflers
http://hdl.handle.net/2117/103790
Numerical analysis of suction mufflers
Rigola Serrano, Joaquim; López Mas, Joan; Papakokkinos, Giorgos; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
The aim of this paper is to present the numerical resolution of suction muffler configurations (by means of a tridimensional, unstructured, parallel and object oriented CFD&HT TermoFluids code (Lehmkuhl, et al. 2007) specially adapted to low Mach models (Lopez et al. 2012), coupled with the numerical resolution of the whole compressor domain (by means of a modular, unstructured and object oriented NEST-compressors tool (Damle et al. 2011) to simulate the thermal and fluid dynamic behavior of hermetic reciprocating compressors). The numerical results aim to evaluate the influence of the suction muffler geometry on the mass flow rate and compressor efficiency performance, while considering the whole compressor working conditions in a coupling manner. In that sense, the CFD&HT resolution of the muffler is obtained with boundary conditions obtained from the numerical simulation of the rest of the hermetic reciprocating compressor. The use of Large Eddy Simulation (LES) models for the turbulent suction muffler analysis; the adaptation of Low Mach formulation avoiding the full incompressible numerical problem, and the coupling of a numerical simulation model of the whole compressor as boundary conditions, are the important updated numerical aspects presented in this paper.
2017-04-27T13:55:50ZRigola Serrano, JoaquimLópez Mas, JoanPapakokkinos, GiorgosLehmkuhl Barba, OriolOliva Llena, AsensioThe aim of this paper is to present the numerical resolution of suction muffler configurations (by means of a tridimensional, unstructured, parallel and object oriented CFD&HT TermoFluids code (Lehmkuhl, et al. 2007) specially adapted to low Mach models (Lopez et al. 2012), coupled with the numerical resolution of the whole compressor domain (by means of a modular, unstructured and object oriented NEST-compressors tool (Damle et al. 2011) to simulate the thermal and fluid dynamic behavior of hermetic reciprocating compressors). The numerical results aim to evaluate the influence of the suction muffler geometry on the mass flow rate and compressor efficiency performance, while considering the whole compressor working conditions in a coupling manner. In that sense, the CFD&HT resolution of the muffler is obtained with boundary conditions obtained from the numerical simulation of the rest of the hermetic reciprocating compressor. The use of Large Eddy Simulation (LES) models for the turbulent suction muffler analysis; the adaptation of Low Mach formulation avoiding the full incompressible numerical problem, and the coupling of a numerical simulation model of the whole compressor as boundary conditions, are the important updated numerical aspects presented in this paper.Characteristics of the near wake region behind a cylinder at critical and super-critical Reynolds numbers
http://hdl.handle.net/2117/103759
Characteristics of the near wake region behind a cylinder at critical and super-critical Reynolds numbers
Rodríguez Pérez, Ivette María; Lehmkuhl Barba, Oriol; Chiva Segura, Jorge; Borrell Pol, Ricard; Oliva Llena, Asensio
Large-eddy simulations (LES) of the flow past a circular cylinder are used to investigate the characteristics of the near wake region at Reynolds numbers Re = 2.5 × 105 - 8.5 × 105. This range encompasses both the critical and super-critical regimes. Wake characteristic lengths are measured and compared between the different Reynolds numbers. It is shown that the super-critical regime is characterised by a plateau in the drag coefficient at about CD ˜ 0.22, and a quasi-stable wake which has a width of dw /D ˜ 0.4. The analysis also shows a steep decrease in the Reynolds stresses when entering the super-critical regime. Furthermore, the overall analysis shows that after the changes occurring at critical Reynolds numbers, the wake enters a regime where its dynamics is quite similar regardless of the Reynolds number.
2017-04-26T15:34:26ZRodríguez Pérez, Ivette MaríaLehmkuhl Barba, OriolChiva Segura, JorgeBorrell Pol, RicardOliva Llena, AsensioLarge-eddy simulations (LES) of the flow past a circular cylinder are used to investigate the characteristics of the near wake region at Reynolds numbers Re = 2.5 × 105 - 8.5 × 105. This range encompasses both the critical and super-critical regimes. Wake characteristic lengths are measured and compared between the different Reynolds numbers. It is shown that the super-critical regime is characterised by a plateau in the drag coefficient at about CD ˜ 0.22, and a quasi-stable wake which has a width of dw /D ˜ 0.4. The analysis also shows a steep decrease in the Reynolds stresses when entering the super-critical regime. Furthermore, the overall analysis shows that after the changes occurring at critical Reynolds numbers, the wake enters a regime where its dynamics is quite similar regardless of the Reynolds number.A dynamic wall model for large eddy simulation on unstructured meshes. Application to wind turbine dedicated airfoils
http://hdl.handle.net/2117/103756
A dynamic wall model for large eddy simulation on unstructured meshes. Application to wind turbine dedicated airfoils
Calafell Sandiumenge, Joan; Lehmkuhl Barba, Oriol; Rodríguez Pérez, Ivette María; Oliva Llena, Asensio; Pérez Segarra, Carlos David
Large eddy simulations (LES) of wall resolved flows at high Reynolds number are still computation-ally demanding. In the present work, a new Dynamic Wall Model (DWM) for LES is presented. The methodology, implemented on unstructured meshes and formulated in a general form, takes into account non-equilibrium effects. The DWM is validated with a channel flow at Ret = 4200 by comparing with direct numerical simulation (DNS) from literature. Once the model is verified, it is used to simulate the flow around a wind turbine dedicated airfoil (DU-93-W-210) in stall condition at Re = 3 × 106. Numerical results shows that the current DWM strategy is capable of accurately capturing the flow detachment and transition to turbulence.
2017-04-26T14:35:10ZCalafell Sandiumenge, JoanLehmkuhl Barba, OriolRodríguez Pérez, Ivette MaríaOliva Llena, AsensioPérez Segarra, Carlos DavidLarge eddy simulations (LES) of wall resolved flows at high Reynolds number are still computation-ally demanding. In the present work, a new Dynamic Wall Model (DWM) for LES is presented. The methodology, implemented on unstructured meshes and formulated in a general form, takes into account non-equilibrium effects. The DWM is validated with a channel flow at Ret = 4200 by comparing with direct numerical simulation (DNS) from literature. Once the model is verified, it is used to simulate the flow around a wind turbine dedicated airfoil (DU-93-W-210) in stall condition at Re = 3 × 106. Numerical results shows that the current DWM strategy is capable of accurately capturing the flow detachment and transition to turbulence.Non-Oberbeck-Boussinesq effects in a turbulent tall water-filled differentially heated cavity
http://hdl.handle.net/2117/103753
Non-Oberbeck-Boussinesq effects in a turbulent tall water-filled differentially heated cavity
Kizildag, Deniz; Rodríguez Pérez, Ivette María; Trias Miquel, Francesc Xavier; Oliva Llena, Asensio; Pérez Segarra, Carlos David
The present work studies the non-Oberbeck-Boussinesq (NOB) effects in a tall water-filled differentially heated cavity by means of direct numerical simulation. The obtained results reveal significant NOB effects for this configuration, due mainly to the dissimilar flow behavior in the vertical boundary layers. Consequently, aspects like the transition to turbulence and flow symmetry are affected. Instantaneous flow structures and mean flow variables are provided in order to gain insight into the complex phenomena such as turbulent mixing and interaction between the hot and cold boundary layers.
2017-04-26T13:45:41ZKizildag, DenizRodríguez Pérez, Ivette MaríaTrias Miquel, Francesc XavierOliva Llena, AsensioPérez Segarra, Carlos DavidThe present work studies the non-Oberbeck-Boussinesq (NOB) effects in a tall water-filled differentially heated cavity by means of direct numerical simulation. The obtained results reveal significant NOB effects for this configuration, due mainly to the dissimilar flow behavior in the vertical boundary layers. Consequently, aspects like the transition to turbulence and flow symmetry are affected. Instantaneous flow structures and mean flow variables are provided in order to gain insight into the complex phenomena such as turbulent mixing and interaction between the hot and cold boundary layers.Building a new subgrid characteristic length for LES
http://hdl.handle.net/2117/103716
Building a new subgrid characteristic length for LES
Trias Miquel, Francesc Xavier; Gorobets, Andrey; Duben, Alexey; Oliva Llena, Asensio
2017-04-25T14:09:34ZTrias Miquel, Francesc XavierGorobets, AndreyDuben, AlexeyOliva Llena, AsensioParallel object-oriented algorithms for building performance simulation. Application to an existing dwelling
http://hdl.handle.net/2117/103680
Parallel object-oriented algorithms for building performance simulation. Application to an existing dwelling
López Mas, Joan; Capdevila Paramio, Roser; Souaihi, Oussama; Rigola Serrano, Joaquim; Oliva Llena, Asensio
In the present work an existing dwelling, situated in the Netherlands, has been modeled by means of a parallel object-oriented simulation tool, called NEST-Buildings. The model is based on a pre-defined collection of elements (e.g., walls, rooms, openings, outdoors, occupants, ventilation tubes and boxes, solar radiation distributors, HVAC equipment, etc.) that are connected to each other conforming a dynamic thermal system. New configurations can be easily handled by adding or removing elements. Moreover, the building elements can be modeled at distinct levels of accuracy ranging from lumped volumes mixed with one-dimensional to detailed CFD&HT models. This approach makes possible the assessment of general-type buildings (residential, services, old, modern, etc.) using the appropriate modeling level at each component. The work is one more step in the improvement of this computer simulation tool. So far, the full simulation of the overall building model is based on block-Jacobi and Gauss-Seidel algorithms. With the current implementation, the computational time for performing practical simulations may become an important impediment as the size of the building increases. For instance, the computational expenses of a family house are far larger than those in a single apartment since the number of rooms, walls, events and so on is bigger. The last advances in this research line, including the use of optimum time stepping, proper mesh sizes, convergence criteria, loop control strategies and the use of other non-linear solvers based on the Newton method, are presented and discussed through comparative analysis of the simulated dwelling. The advances in this direction will help first to better understand the behavior of the already available algorithms and later to speed up the simulations. The second is important in the attainment of optimal designs of dwellings or other type of buildings.
2017-04-24T14:37:11ZLópez Mas, JoanCapdevila Paramio, RoserSouaihi, OussamaRigola Serrano, JoaquimOliva Llena, AsensioIn the present work an existing dwelling, situated in the Netherlands, has been modeled by means of a parallel object-oriented simulation tool, called NEST-Buildings. The model is based on a pre-defined collection of elements (e.g., walls, rooms, openings, outdoors, occupants, ventilation tubes and boxes, solar radiation distributors, HVAC equipment, etc.) that are connected to each other conforming a dynamic thermal system. New configurations can be easily handled by adding or removing elements. Moreover, the building elements can be modeled at distinct levels of accuracy ranging from lumped volumes mixed with one-dimensional to detailed CFD&HT models. This approach makes possible the assessment of general-type buildings (residential, services, old, modern, etc.) using the appropriate modeling level at each component. The work is one more step in the improvement of this computer simulation tool. So far, the full simulation of the overall building model is based on block-Jacobi and Gauss-Seidel algorithms. With the current implementation, the computational time for performing practical simulations may become an important impediment as the size of the building increases. For instance, the computational expenses of a family house are far larger than those in a single apartment since the number of rooms, walls, events and so on is bigger. The last advances in this research line, including the use of optimum time stepping, proper mesh sizes, convergence criteria, loop control strategies and the use of other non-linear solvers based on the Newton method, are presented and discussed through comparative analysis of the simulated dwelling. The advances in this direction will help first to better understand the behavior of the already available algorithms and later to speed up the simulations. The second is important in the attainment of optimal designs of dwellings or other type of buildings.On the use of a parallel object-oriented code for solving the heat transfer in hermetic reciprocating compressors
http://hdl.handle.net/2117/103677
On the use of a parallel object-oriented code for solving the heat transfer in hermetic reciprocating compressors
López Mas, Joan; Rigola Serrano, Joaquim; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
The heat transport phenomenon in a hermetic reciprocating compressor is addressed in this work. This is far from straightforward. It involves several transient physical phenomena interacting to each other. The heat is exchanged between the refrigerant fluid and the solid parts of the compressor (suction muffler, cylinder head, crankcase, etc.). At the same time, the solid parts exchange heat to each other by means of conduction and radiation. Moreover, the phenomenon happens in non-symmetrical complex geometries and the solid parts are made of different materials. This is interesting from both the software engineering and the compressor design viewpoint. A parallel object-oriented software platform for the resolution of multiphysics problems is employed. This platform allows the use of partitioned strategies so that the compressor heat transport problem -a global problem- can be divided into several smaller parts -local problems-. This makes possible the use of multilevel modeling strategies for thermal systems analysis. Furthermore, in order to couple the several sub-problems in an integrated simulation, the platform provides data transfer tools -for matching and non-matching meshes- to exchange sub-domain state information. In particular, the work provides detailed information on the heat distribution and the temperature of the components of a test compressor. By means of comparative studies the thermal properties of some of its components are analyzed. This highlights the importance of choosing proper materials. For example, different suction muffler materials are tested to investigate their influence on the volumetric efficiency. Since the whole compressor is simulated, the consequences of altering specific component properties are also appreciated on the other components. In sum, the work presents illustrative numerical results of the three-dimensional heat transfer in a compressor that show the potential use of computer simulation to support design of components to attain feasibility and energy efficiency.
2017-04-24T12:18:16ZLópez Mas, JoanRigola Serrano, JoaquimLehmkuhl Barba, OriolOliva Llena, AsensioThe heat transport phenomenon in a hermetic reciprocating compressor is addressed in this work. This is far from straightforward. It involves several transient physical phenomena interacting to each other. The heat is exchanged between the refrigerant fluid and the solid parts of the compressor (suction muffler, cylinder head, crankcase, etc.). At the same time, the solid parts exchange heat to each other by means of conduction and radiation. Moreover, the phenomenon happens in non-symmetrical complex geometries and the solid parts are made of different materials. This is interesting from both the software engineering and the compressor design viewpoint. A parallel object-oriented software platform for the resolution of multiphysics problems is employed. This platform allows the use of partitioned strategies so that the compressor heat transport problem -a global problem- can be divided into several smaller parts -local problems-. This makes possible the use of multilevel modeling strategies for thermal systems analysis. Furthermore, in order to couple the several sub-problems in an integrated simulation, the platform provides data transfer tools -for matching and non-matching meshes- to exchange sub-domain state information. In particular, the work provides detailed information on the heat distribution and the temperature of the components of a test compressor. By means of comparative studies the thermal properties of some of its components are analyzed. This highlights the importance of choosing proper materials. For example, different suction muffler materials are tested to investigate their influence on the volumetric efficiency. Since the whole compressor is simulated, the consequences of altering specific component properties are also appreciated on the other components. In sum, the work presents illustrative numerical results of the three-dimensional heat transfer in a compressor that show the potential use of computer simulation to support design of components to attain feasibility and energy efficiency.3D compressible simulation of a muffler with pseudosound prediction levels
http://hdl.handle.net/2117/103630
3D compressible simulation of a muffler with pseudosound prediction levels
Ruano Pérez, Jesús; López Mas, Joan; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; Pérez Segarra, Carlos David
The main objective of this paper is to present a numerical resolution of a suction muffler configuration by using an in-house object oriented CFD & HT code TermoFluids (Lehmkuhl et al. 2007), able to handle tridimensional geometries, unstructured meshes and parallelization availability. This code has been adapted to be able to resolute 3D Navier-Stokes equations in their compressible form and coupled with the numerical resolution of the whole compressor domain by means of a parallel and object-oriented called NEST tool (Lopez, 2016). The numerical results aim to study the influence of the suction muffler inner geometry in the fluidynamic behavior inside the muffler while considering how this internal geometry affects the global performance of the compressor. Hence, the inlet and outlet boundary conditions at the muffler are obtained from the numerical simulation of the whole compressor using NEST, while the fluid behavior inside the muffler is numerically simulated by means of detailed analysis. In addition, the paper presents a methodology that handles with Large Eddy Simulation (LES) models for the turbulent motion of fluid inside the muffler, the formulation of Navier-Stokes in their compressible form, dealing with numerical problems derived from the compressible part, and the coupling of the whole compressor simulation to set boundary condition. Finally, the obtained results will be compared with the empirical data obtained in the CTTC facilities from the study of a real muffler placed in a reciprocating compressor.
2017-04-21T13:44:50ZRuano Pérez, JesúsLópez Mas, JoanLehmkuhl Barba, OriolRigola Serrano, JoaquimPérez Segarra, Carlos DavidThe main objective of this paper is to present a numerical resolution of a suction muffler configuration by using an in-house object oriented CFD & HT code TermoFluids (Lehmkuhl et al. 2007), able to handle tridimensional geometries, unstructured meshes and parallelization availability. This code has been adapted to be able to resolute 3D Navier-Stokes equations in their compressible form and coupled with the numerical resolution of the whole compressor domain by means of a parallel and object-oriented called NEST tool (Lopez, 2016). The numerical results aim to study the influence of the suction muffler inner geometry in the fluidynamic behavior inside the muffler while considering how this internal geometry affects the global performance of the compressor. Hence, the inlet and outlet boundary conditions at the muffler are obtained from the numerical simulation of the whole compressor using NEST, while the fluid behavior inside the muffler is numerically simulated by means of detailed analysis. In addition, the paper presents a methodology that handles with Large Eddy Simulation (LES) models for the turbulent motion of fluid inside the muffler, the formulation of Navier-Stokes in their compressible form, dealing with numerical problems derived from the compressible part, and the coupling of the whole compressor simulation to set boundary condition. Finally, the obtained results will be compared with the empirical data obtained in the CTTC facilities from the study of a real muffler placed in a reciprocating compressor.