Ponències/Comunicacions de congressos
http://hdl.handle.net/2117/3992
2017-04-26T14:04:23ZNon-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.Virtual household refrigerators at steady-state and transient conditions. Numerical model and experimental validation
http://hdl.handle.net/2117/103624
Virtual household refrigerators at steady-state and transient conditions. Numerical model and experimental validation
Ablanque Mejía, Nicolás; Oliet Casasayas, Carles; Rigola Serrano, Joaquim; Pérez Segarra, Carlos David
The current status of a flexible numerical model for vapor compression refrigeration systems for steady state and transient conditions is presented. The model simulates both the refrigeration cycle itself and the refrigerated compartments network, based on a modular approach, where each element of the system is solved independently by means of appropriate models, and where the whole system is solved iteratively based on the links established between the elements. The methodology implemented to achieve the transient simulation of the whole system combines a steady-state approach for the refrigerating cycle loop with a transient approach for the refrigerated compartments.
The aim of this work is to review the model validation at steady-state conditions for a particular refrigerator with a unique refrigerated cabinet and to perform transient simulations in order to foresee the refrigerator behavior. The main components of the studied refrigerator, namely, hermetic compressor, wire-and-tube condenser, non-adiabatic
capillary tube, plate evaporator, low-pressure-side accumulator, and refrigerated cabinet, are included in the model. On the one hand, for steady state conditions, both the system relevant temperatures and the refrigerant charge distribution are predicted at different heat loads and compared against experimental values. On the other hand, for
transient conditions, the evolution in time of both the system relevant temperatures and the refrigerant charge distribution is analyzed.
2017-04-21T12:49:57ZAblanque Mejía, NicolásOliet Casasayas, CarlesRigola Serrano, JoaquimPérez Segarra, Carlos DavidThe current status of a flexible numerical model for vapor compression refrigeration systems for steady state and transient conditions is presented. The model simulates both the refrigeration cycle itself and the refrigerated compartments network, based on a modular approach, where each element of the system is solved independently by means of appropriate models, and where the whole system is solved iteratively based on the links established between the elements. The methodology implemented to achieve the transient simulation of the whole system combines a steady-state approach for the refrigerating cycle loop with a transient approach for the refrigerated compartments.
The aim of this work is to review the model validation at steady-state conditions for a particular refrigerator with a unique refrigerated cabinet and to perform transient simulations in order to foresee the refrigerator behavior. The main components of the studied refrigerator, namely, hermetic compressor, wire-and-tube condenser, non-adiabatic
capillary tube, plate evaporator, low-pressure-side accumulator, and refrigerated cabinet, are included in the model. On the one hand, for steady state conditions, both the system relevant temperatures and the refrigerant charge distribution are predicted at different heat loads and compared against experimental values. On the other hand, for
transient conditions, the evolution in time of both the system relevant temperatures and the refrigerant charge distribution is analyzed.Fluid-structure interaction of a reed type valve
http://hdl.handle.net/2117/103594
Fluid-structure interaction of a reed type valve
González Acedo, Ignacio; Lehmkuhl Barba, Oriol; Naseri, Alireza; Rigola Serrano, Joaquim; Oliva Llena, Asensio
This paper presents a complete numerical procedure to study the fluid-structure interaction problem of incompressible flow through reed valves, typically employed in hermetic reciprocating compressors. A partitioned semi-implicit coupling scheme is implemented, which only strongly couples the added-mass-effect (pressure term) of the fluid to the structure hence, assuring numerical stability and avoiding excessive computational cost. The fluid is solved by a three-dimensional CFD solver using large eddy simulation closures to model the turbulent flow, while the reed valve is described with the classical plate theory and the normal mode summation method. To showcase the potentiality of the proposed methodology, a sensitivity analysis regarding valve thickness is carried out for a given velocity in the feeding channel. Considerable differences, mainly in valve lift and pressure drop, are appreciated between the considered configurations.
2017-04-20T15:34:01ZGonzález Acedo, IgnacioLehmkuhl Barba, OriolNaseri, AlirezaRigola Serrano, JoaquimOliva Llena, AsensioThis paper presents a complete numerical procedure to study the fluid-structure interaction problem of incompressible flow through reed valves, typically employed in hermetic reciprocating compressors. A partitioned semi-implicit coupling scheme is implemented, which only strongly couples the added-mass-effect (pressure term) of the fluid to the structure hence, assuring numerical stability and avoiding excessive computational cost. The fluid is solved by a three-dimensional CFD solver using large eddy simulation closures to model the turbulent flow, while the reed valve is described with the classical plate theory and the normal mode summation method. To showcase the potentiality of the proposed methodology, a sensitivity analysis regarding valve thickness is carried out for a given velocity in the feeding channel. Considerable differences, mainly in valve lift and pressure drop, are appreciated between the considered configurations.The effects of roughness on the boundary layer development of a circular cylinder
http://hdl.handle.net/2117/103589
The effects of roughness on the boundary layer development of a circular cylinder
Rodríguez Pérez, Ivette María; Lehmkuhl Barba, Oriol; Piomelli, Ugo; Chiva Segura, Jorge; Borrell, Ricard; Oliva Llena, Asensio
This paper focuses on the effects of surface roughness in the flow past a circular cylinder at different Reynolds numbers. Large eddy simulations of the flow, from subcritical to transcritical Reynolds numbers and at relatively high equivalent sand grain roughness of ks / D = 0:02 are performed. In order to determine the effects of the surface roughness on the boundary layer transition and as a consequence on the wake topology, results are compared to literature available data for the rough and smooth cylinders. Results show that surface roughness triggers the transition to turbulence in the boundary layer at all Reynolds numbers, thus leading to an early separation caused by the increased drag and momentum deficit. In fact, even at subcritical Reynolds numbers boundary layer instabilities are triggered in the roughness sublayer which
eventually lead to the transition to turbulence and the separation before the cylinder apex. For the transcritical Reynolds number (i.e. Re = 4:2x105), transition to turbulence is observed in the attached boundary layer. Largest changes in the flow topology are observed at Re = 4:2x105, as the wake is wider than that of the smooth cylinder at these Reynolds numbers, with larger Reynolds stresses along the boundary layer and the near wake.
2017-04-20T14:52:23ZRodríguez Pérez, Ivette MaríaLehmkuhl Barba, OriolPiomelli, UgoChiva Segura, JorgeBorrell, RicardOliva Llena, AsensioThis paper focuses on the effects of surface roughness in the flow past a circular cylinder at different Reynolds numbers. Large eddy simulations of the flow, from subcritical to transcritical Reynolds numbers and at relatively high equivalent sand grain roughness of ks / D = 0:02 are performed. In order to determine the effects of the surface roughness on the boundary layer transition and as a consequence on the wake topology, results are compared to literature available data for the rough and smooth cylinders. Results show that surface roughness triggers the transition to turbulence in the boundary layer at all Reynolds numbers, thus leading to an early separation caused by the increased drag and momentum deficit. In fact, even at subcritical Reynolds numbers boundary layer instabilities are triggered in the roughness sublayer which
eventually lead to the transition to turbulence and the separation before the cylinder apex. For the transcritical Reynolds number (i.e. Re = 4:2x105), transition to turbulence is observed in the attached boundary layer. Largest changes in the flow topology are observed at Re = 4:2x105, as the wake is wider than that of the smooth cylinder at these Reynolds numbers, with larger Reynolds stresses along the boundary layer and the near wake.A complete analysis of the heat, air and moisture transfer on building performance
http://hdl.handle.net/2117/103576
A complete analysis of the heat, air and moisture transfer on building performance
Souaihi, Oussama; Lopez, Joan; Capdevila Paramio, Roser; Rigola Serrano, Joaquim; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
The simulation of combined heat, air and moisture (HAM) is important to predict the indoor air quality and thermal comfort. Moreover, inappropriate levels of indoor humidity and temperature can contribute to a high movement of water vapor through the building walls, causing deterioration and reduction of the thermal insulation which leads to higher energy demand. The simulation of the buildings behavior can help to optimize the design of new or existing building, help better control the HVAC system and therefore results in energy efficient buildings.
In this work, an in-house modular object-oriented tool (NEST) for the multiphysics simulation of buildings is presented. The whole building is modeled as a collection of basic elements (e.g., walls, rooms, openings, occupancy, HVAC system, solar radiation distributor, etc.). These elements can be modeled using different physical models and scales. A combined heat, air and moisture transfer model for the building envelopes and rooms have been implemented and validated with different benchmark cases. The in-house simulation tool has been used for the simulation of hygrothermal behavior of rooms inside different public buildings (residential apartments, hospital rooms, universities and school plants). The simulations allowed as the analysis of the humidity effect on thermal comfort and energy performance of the rooms.
2017-04-20T12:49:50ZSouaihi, OussamaLopez, JoanCapdevila Paramio, RoserRigola Serrano, JoaquimLehmkuhl Barba, OriolOliva Llena, AsensioThe simulation of combined heat, air and moisture (HAM) is important to predict the indoor air quality and thermal comfort. Moreover, inappropriate levels of indoor humidity and temperature can contribute to a high movement of water vapor through the building walls, causing deterioration and reduction of the thermal insulation which leads to higher energy demand. The simulation of the buildings behavior can help to optimize the design of new or existing building, help better control the HVAC system and therefore results in energy efficient buildings.
In this work, an in-house modular object-oriented tool (NEST) for the multiphysics simulation of buildings is presented. The whole building is modeled as a collection of basic elements (e.g., walls, rooms, openings, occupancy, HVAC system, solar radiation distributor, etc.). These elements can be modeled using different physical models and scales. A combined heat, air and moisture transfer model for the building envelopes and rooms have been implemented and validated with different benchmark cases. The in-house simulation tool has been used for the simulation of hygrothermal behavior of rooms inside different public buildings (residential apartments, hospital rooms, universities and school plants). The simulations allowed as the analysis of the humidity effect on thermal comfort and energy performance of the rooms.Energy simulation of a single family dwelling as a test bench for climate control system assessment
http://hdl.handle.net/2117/103558
Energy simulation of a single family dwelling as a test bench for climate control system assessment
Capdevila Paramio, Roser; Souaihi, Oussama; Lopez, Joan; Rigola Serrano, Joaquim; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
In the present work a real dwelling (a semi-detached house in the Netherlands) has been modelled with an in-house modular object-oriented building simulation tool, called NEST-Buildings. This software models the whole building as a collection of elements (e.g., walls, rooms, outdoors, people, ventilation tubes and boxes, solar radiation distributor, HVAC, airflow, CO2 transport, etc.) connected between them through boundary conditions. Special emphasis has been given to the airflow model of the house.
The main objective of the modellization of a real dwelling is to use it as a test bench for a new affordable, easy to use and apply, integral dwelling climate control system called DCCS (Dwelling Climate Control System), whose one of its objectives is reducing the energy use of buildings by optimizing the parameters of the heating and the ventilation system and ensuring the indoor quality inside the dwelling (by means of CO2 concentration control).
In the present paper the effect of different control strategies on the energy performance of the house as well as on the quality of the air has been analysed.
2017-04-19T18:09:29ZCapdevila Paramio, RoserSouaihi, OussamaLopez, JoanRigola Serrano, JoaquimLehmkuhl Barba, OriolOliva Llena, AsensioIn the present work a real dwelling (a semi-detached house in the Netherlands) has been modelled with an in-house modular object-oriented building simulation tool, called NEST-Buildings. This software models the whole building as a collection of elements (e.g., walls, rooms, outdoors, people, ventilation tubes and boxes, solar radiation distributor, HVAC, airflow, CO2 transport, etc.) connected between them through boundary conditions. Special emphasis has been given to the airflow model of the house.
The main objective of the modellization of a real dwelling is to use it as a test bench for a new affordable, easy to use and apply, integral dwelling climate control system called DCCS (Dwelling Climate Control System), whose one of its objectives is reducing the energy use of buildings by optimizing the parameters of the heating and the ventilation system and ensuring the indoor quality inside the dwelling (by means of CO2 concentration control).
In the present paper the effect of different control strategies on the energy performance of the house as well as on the quality of the air has been analysed.