CTTC - Centre Tecnològic de la Transferència de Calor
http://hdl.handle.net/2117/3190
Sat, 30 Apr 2016 21:19:39 GMT2016-04-30T21:19:39ZTurbulent flow around a square cylinder at Reynolds number 22,000: A DNS study
http://hdl.handle.net/2117/86080
Turbulent flow around a square cylinder at Reynolds number 22,000: A DNS study
Trias Miquel, Francesc Xavier; Gorobets, Andrei; Oliva Llena, Asensio
The turbulent flow around a square cylinder at Reynolds number 22,000 (based on the cylinder diameter and the inflow velocity) is studied by means of direct numerical simulation. An overview of the numerical methods and the methodology used to verify the simulation is presented with special emphasis to determine the proper domain size and time-integration period. Then, the time-averaged flow results and turbulent statistics are discussed together with available experimental data showing a fairly good agreement. Finally, frequency analysis of velocity samples is used to analyze both the Kelvin-Helmholtz vortical structures produced by the flow separation at the leading edge of the cylinder and the Von Karman vortex shedding in the wake region. The former are observed more downstream compared with the experiments suggesting that transition to turbulence may occur later. However, comparison of the turbulent statistics in the near wall region indicates that transition is being well captured.
Thu, 21 Apr 2016 16:00:15 GMThttp://hdl.handle.net/2117/860802016-04-21T16:00:15ZTrias Miquel, Francesc XavierGorobets, AndreiOliva Llena, AsensioThe turbulent flow around a square cylinder at Reynolds number 22,000 (based on the cylinder diameter and the inflow velocity) is studied by means of direct numerical simulation. An overview of the numerical methods and the methodology used to verify the simulation is presented with special emphasis to determine the proper domain size and time-integration period. Then, the time-averaged flow results and turbulent statistics are discussed together with available experimental data showing a fairly good agreement. Finally, frequency analysis of velocity samples is used to analyze both the Kelvin-Helmholtz vortical structures produced by the flow separation at the leading edge of the cylinder and the Von Karman vortex shedding in the wake region. The former are observed more downstream compared with the experiments suggesting that transition to turbulence may occur later. However, comparison of the turbulent statistics in the near wall region indicates that transition is being well captured.Direct numerical simulation of a fully developed turbulent square duct flow up to Re-tau=1200
http://hdl.handle.net/2117/86076
Direct numerical simulation of a fully developed turbulent square duct flow up to Re-tau=1200
Zhang, Hao; Trias Miquel, Francesc Xavier; Gorobets, Andrey; Tan, Yuanqiang; Oliva Llena, Asensio
Various fundamental studies based on a turbulent duct flow have gained popularity including heat transfer, magnetohydrodynamics as well as particle-laden transportation. An accurate prediction on the turbulent flow field is critical for these researches. However, the database of the mean flow and turbulence statistics is fairly insufficient due to the enormous cost of numerical simulation at high Reynolds number. This paper aims at providing available information by conducting several Direct Numerical Simulations (DNS) on turbulent duct flows at Re-tau = 300, 600, 900 and 1200. A quantitative comparison between current and previous DNS results was performed where a good agreement was achieved at Re-tau = 300. However, further comparisons of the present results with the previous DNS results at Re-tau = 600 obtained with much coarser meshes revealed some discrepancies which can be explained by the insufficient mesh resolution. At last, the mean flow and turbulent statistics at higher Re-tau was presented and the effect of Re-tau on the mean flow and flow dynamics was discussed.
Thu, 21 Apr 2016 14:52:02 GMThttp://hdl.handle.net/2117/860762016-04-21T14:52:02ZZhang, HaoTrias Miquel, Francesc XavierGorobets, AndreyTan, YuanqiangOliva Llena, AsensioVarious fundamental studies based on a turbulent duct flow have gained popularity including heat transfer, magnetohydrodynamics as well as particle-laden transportation. An accurate prediction on the turbulent flow field is critical for these researches. However, the database of the mean flow and turbulence statistics is fairly insufficient due to the enormous cost of numerical simulation at high Reynolds number. This paper aims at providing available information by conducting several Direct Numerical Simulations (DNS) on turbulent duct flows at Re-tau = 300, 600, 900 and 1200. A quantitative comparison between current and previous DNS results was performed where a good agreement was achieved at Re-tau = 300. However, further comparisons of the present results with the previous DNS results at Re-tau = 600 obtained with much coarser meshes revealed some discrepancies which can be explained by the insufficient mesh resolution. At last, the mean flow and turbulent statistics at higher Re-tau was presented and the effect of Re-tau on the mean flow and flow dynamics was discussed.Numerical analysis of the turbulent fluid flow through valves. Geometrical aspects influence at different positions
http://hdl.handle.net/2117/85986
Numerical analysis of the turbulent fluid flow through valves. Geometrical aspects influence at different positions
Rigola Serrano, Joaquim; Aljure Osorio, David E.; Lehmkuhl Barba, Oriol; Pérez Segarra, Carlos David; Oliva Llena, Asensio
The aim of this paper is to carry out a group of numerical experiments over the fluid flow through a valve reed, using the CFD&HT code TermoFluids, an unstructured and parallel object-oriented CFD code for accurate and reliable solving of industrial flows. Turbulent flow and its solution is a very complex problem due to there is a non-lineal interaction between viscous and inertial effects further complicated by their rotational nature, together with the three-dimensionality inherent in these types of flow and the non-steady state solutions. In this work, different meshes, geometrical conditions and LES turbulence models (WALE, VMS, QR and SIGMA) are tested and results compared. On the other hand, the fluid flow boundary conditions are obtained by means of the numerical simulation model of hermetic reciprocating compressors tool, NEST-compressor code. The numerical results presented are based on a specific geometry, where the valve gap opening percentage is 11% of hole diameter and Reynolds numbers given by the one-dimensional model is 4.22 × 105, with density meshes of approximately 8 million CVs. Geometrical aspects related with the orifice's shape and its influence on fluid flow behaviour and pressure drop are analysed in detail, furthermore, flow results for different valve openings are also studied.
Published under licence in IOP Conference Series: Materials Science and Engineering by IOP Publishing Ltd.
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Wed, 20 Apr 2016 13:46:11 GMThttp://hdl.handle.net/2117/859862016-04-20T13:46:11ZRigola Serrano, JoaquimAljure Osorio, David E.Lehmkuhl Barba, OriolPérez Segarra, Carlos DavidOliva Llena, AsensioThe aim of this paper is to carry out a group of numerical experiments over the fluid flow through a valve reed, using the CFD&HT code TermoFluids, an unstructured and parallel object-oriented CFD code for accurate and reliable solving of industrial flows. Turbulent flow and its solution is a very complex problem due to there is a non-lineal interaction between viscous and inertial effects further complicated by their rotational nature, together with the three-dimensionality inherent in these types of flow and the non-steady state solutions. In this work, different meshes, geometrical conditions and LES turbulence models (WALE, VMS, QR and SIGMA) are tested and results compared. On the other hand, the fluid flow boundary conditions are obtained by means of the numerical simulation model of hermetic reciprocating compressors tool, NEST-compressor code. The numerical results presented are based on a specific geometry, where the valve gap opening percentage is 11% of hole diameter and Reynolds numbers given by the one-dimensional model is 4.22 × 105, with density meshes of approximately 8 million CVs. Geometrical aspects related with the orifice's shape and its influence on fluid flow behaviour and pressure drop are analysed in detail, furthermore, flow results for different valve openings are also studied.PIBM: Particulate immersed boundary method for fluid-particle interaction problems
http://hdl.handle.net/2117/85915
PIBM: Particulate immersed boundary method for fluid-particle interaction problems
Zhang, Hao; Trias Miquel, Francesc Xavier; Oliva Llena, Asensio; Yang, Dongmin; Tan, Yuanqiang; Shu, Shi; Sheng, Yong
It is well known that the number of particles should be scaled up to enable industrial scale simulation. The calculations are more computationally intensive when the motion of the surrounding fluid is considered. Besides the advances in computer hardware and numerical algorithms, the coupling scheme also plays an important role on the computational efficiency. In this study, a particulate immersed boundary method (PIBM) for simulating the fluid-particle multiphase flow was presented and assessed in both two- and three-dimensional applications. The idea behind PIBM derives from the conventional momentum exchange-based Immersed Boundary Method (IBM) by treating each Lagrangian point as a solid particle. This treatment enables Lattice Boltzmann Method (LBM) to be coupled with fine particles residing within a particular grid cell. Compared with the conventional IBM, dozens of times speedup in two-dimensional simulation and hundreds of times in three-dimensional simulation can be expected under the same particle and mesh number. Numerical simulations of particle sedimentation in Newtonian flows were canducted based on a combined LBM-PIBM-Discrete Element Method (DEM) scheme, showing that the PIBM can capture the feature of particulate flows in fluid and is indeed a promising scheme for the solution of the fluid-particle interaction problems.
Tue, 19 Apr 2016 14:57:07 GMThttp://hdl.handle.net/2117/859152016-04-19T14:57:07ZZhang, HaoTrias Miquel, Francesc XavierOliva Llena, AsensioYang, DongminTan, YuanqiangShu, ShiSheng, YongIt is well known that the number of particles should be scaled up to enable industrial scale simulation. The calculations are more computationally intensive when the motion of the surrounding fluid is considered. Besides the advances in computer hardware and numerical algorithms, the coupling scheme also plays an important role on the computational efficiency. In this study, a particulate immersed boundary method (PIBM) for simulating the fluid-particle multiphase flow was presented and assessed in both two- and three-dimensional applications. The idea behind PIBM derives from the conventional momentum exchange-based Immersed Boundary Method (IBM) by treating each Lagrangian point as a solid particle. This treatment enables Lattice Boltzmann Method (LBM) to be coupled with fine particles residing within a particular grid cell. Compared with the conventional IBM, dozens of times speedup in two-dimensional simulation and hundreds of times in three-dimensional simulation can be expected under the same particle and mesh number. Numerical simulations of particle sedimentation in Newtonian flows were canducted based on a combined LBM-PIBM-Discrete Element Method (DEM) scheme, showing that the PIBM can capture the feature of particulate flows in fluid and is indeed a promising scheme for the solution of the fluid-particle interaction problems.On the flow past a circular cylinder from critical to super-critical Reynolds numbers: Wake topology and vortex shedding
http://hdl.handle.net/2117/85914
On the flow past a circular cylinder from critical to super-critical Reynolds numbers: Wake topology and vortex shedding
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 flow topology and the vortex shedding process at Reynolds numbers Re=2.5×105-8.5×105Re=2.5×105-8.5×105. This range encompasses both the critical and super-critical regimes. As the flow enters the critical regime, major changes occur which affect the flow configuration. Asymmetries in the flow are found in the critical regime, whereas the wake recovers its symmetry and stabilizes in the super-critical regime. 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˜0.22CD˜0.22, and a quasi-stable wake which has a non-dimensional width of dw/D˜0.4dw/D˜0.4. The periodic nature of the flow is analysed by means of measurements of the unsteady drag and lift coefficients. Power spectra of the lift fluctuations are computed. Wake vortex shedding is found to occur for both regimes investigated, although a jump in frequencies is observed when the flow enters the super-critical regime. In this regime, non-dimensional vortex-shedding frequency is almost constant and equal to St=fvsD/Uref˜0.44St=fvsD/Uref˜0.44. The analysis also shows a steep decrease in the fluctuating lift when entering the super-critical regime. The combined analysis of both wake topology and vortex shedding complements the physical picture of a stable and highly coherent flow in the super-critical regime.
Tue, 19 Apr 2016 14:15:46 GMThttp://hdl.handle.net/2117/859142016-04-19T14:15:46ZRodríguez 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 flow topology and the vortex shedding process at Reynolds numbers Re=2.5×105-8.5×105Re=2.5×105-8.5×105. This range encompasses both the critical and super-critical regimes. As the flow enters the critical regime, major changes occur which affect the flow configuration. Asymmetries in the flow are found in the critical regime, whereas the wake recovers its symmetry and stabilizes in the super-critical regime. 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˜0.22CD˜0.22, and a quasi-stable wake which has a non-dimensional width of dw/D˜0.4dw/D˜0.4. The periodic nature of the flow is analysed by means of measurements of the unsteady drag and lift coefficients. Power spectra of the lift fluctuations are computed. Wake vortex shedding is found to occur for both regimes investigated, although a jump in frequencies is observed when the flow enters the super-critical regime. In this regime, non-dimensional vortex-shedding frequency is almost constant and equal to St=fvsD/Uref˜0.44St=fvsD/Uref˜0.44. The analysis also shows a steep decrease in the fluctuating lift when entering the super-critical regime. The combined analysis of both wake topology and vortex shedding complements the physical picture of a stable and highly coherent flow in the super-critical regime.Numerical evaluation of multi-layered solid-PCM thermocline-like tanks as thermal energy storage systems for CSP applications
http://hdl.handle.net/2117/85680
Numerical evaluation of multi-layered solid-PCM thermocline-like tanks as thermal energy storage systems for CSP applications
Galione Klot, Pedro Andrés; Pérez Segarra, Carlos David; Rodríguez Pérez, Ivette María; Torras Ortiz, Santiago; Rigola Serrano, Joaquim
The two-tank system is the technology used for thermal energy storage (TES) in current concentrating solar power (CSP) plants. Thermocline storage concept has been considered for more than a decade as a possible solution to reduce the high cost of the storage system in these plants. In previous works, multi-layered solid-PCM (MLSPCM) thermocline-like storage tank configurations has been introduced and studied, giving promising results for their use as thermal energy storage systems for CSP. In this work, further analysis is performed in the use of this new concept of TES, by considering variable inlet conditions, and simulating the tank shell and the foundation. The numerical simulations are based on a modular object-oriented methodology. Energetic and exergetic results are presented and compared against a reference 2-tank case and against different thermocline configurations with either solid or phase change filler materials. Again, promising results are obtained for the tested MLSPCM concept.
Thu, 14 Apr 2016 13:13:55 GMThttp://hdl.handle.net/2117/856802016-04-14T13:13:55ZGalione Klot, Pedro AndrésPérez Segarra, Carlos DavidRodríguez Pérez, Ivette MaríaTorras Ortiz, SantiagoRigola Serrano, JoaquimThe two-tank system is the technology used for thermal energy storage (TES) in current concentrating solar power (CSP) plants. Thermocline storage concept has been considered for more than a decade as a possible solution to reduce the high cost of the storage system in these plants. In previous works, multi-layered solid-PCM (MLSPCM) thermocline-like storage tank configurations has been introduced and studied, giving promising results for their use as thermal energy storage systems for CSP. In this work, further analysis is performed in the use of this new concept of TES, by considering variable inlet conditions, and simulating the tank shell and the foundation. The numerical simulations are based on a modular object-oriented methodology. Energetic and exergetic results are presented and compared against a reference 2-tank case and against different thermocline configurations with either solid or phase change filler materials. Again, promising results are obtained for the tested MLSPCM concept.Numerical simulation of non-adiabatic capillary tubes. Special emphasis on the near-saturation zone
http://hdl.handle.net/2117/85629
Numerical simulation of non-adiabatic capillary tubes. Special emphasis on the near-saturation zone
Ablanque Mejía, Nicolás; Oliet Casasayas, Carles; Rigola Serrano, Joaquim; Oliva Llena, Asensio
The aim of this article is to present a distributed numerical model that simulates the thermal and fluid-dynamic phenomena inside non-adiabatic capillary tubes. The resolution approach is based on a two-phase flow model where the fluid domain is discretized in a one-dimensional way, and the governing equations (continuity, momentum, and energy) are solved by means of a step-by-step algorithm. The model explained herein consists of an improved and extended version of previous works (Escanes et al., 1995; García-Valladares et al., 2002a,b; Ablanque et al., 2010) including two additional features. On the one hand, it allows the simulation of the two typical geometric arrangements found in capillary-tube/suction-line heat exchangers (i.e. concentric and lateral). On the other hand, it has an enhanced capability to address the convergence difficulties found in distributed models at the near-saturation zone. This document presents the major numerical adaptations done to the model, a comprehensive validation of the two geometric configurations, the model performance when tackling the aforementioned numerical difficulties and finally, some numerical studies.
Wed, 13 Apr 2016 16:22:34 GMThttp://hdl.handle.net/2117/856292016-04-13T16:22:34ZAblanque Mejía, NicolásOliet Casasayas, CarlesRigola Serrano, JoaquimOliva Llena, AsensioThe aim of this article is to present a distributed numerical model that simulates the thermal and fluid-dynamic phenomena inside non-adiabatic capillary tubes. The resolution approach is based on a two-phase flow model where the fluid domain is discretized in a one-dimensional way, and the governing equations (continuity, momentum, and energy) are solved by means of a step-by-step algorithm. The model explained herein consists of an improved and extended version of previous works (Escanes et al., 1995; García-Valladares et al., 2002a,b; Ablanque et al., 2010) including two additional features. On the one hand, it allows the simulation of the two typical geometric arrangements found in capillary-tube/suction-line heat exchangers (i.e. concentric and lateral). On the other hand, it has an enhanced capability to address the convergence difficulties found in distributed models at the near-saturation zone. This document presents the major numerical adaptations done to the model, a comprehensive validation of the two geometric configurations, the model performance when tackling the aforementioned numerical difficulties and finally, some numerical studies.Building proper invariants for eddy-viscosity subgrid-scale models
http://hdl.handle.net/2117/85302
Building proper invariants for eddy-viscosity subgrid-scale models
Trias Miquel, Francesc Xavier; Folch, David; Gorobets, Andrei; Oliva Llena, Asensio
Direct simulations of the incompressible Navier-Stokes equations are limited to relatively low-Reynolds numbers. Hence, dynamically less complex mathematical formulations are necessary for coarse-grain simulations. Eddy-viscosity models for large-eddy simulation is probably the most popular example thereof: they rely on differential operators that should properly detect different flow configurations (laminar and 2D flows, near-wall behavior, transitional regime, etc.). Most of them are based on the combination of invariants of a symmetric tensor that depends on the gradient of the resolved velocity field, . In this work, models are presented within a framework consisting of a 5D phase space of invariants. In this way, new models can be constructed by imposing appropriate restrictions in this space. For instance, considering the three invariants P GG T , Q GG T , and R GG T of the tensorGG T , and imposing the proper cubic near-wall behavior, i.e., , we deduce that the eddy-viscosity is given by . Moreover, only R GG T -dependent models, i.e., p > - 5/2, switch off for 2D flows. Finally, the model constant may be related with the Vreman’s model constant via ; this guarantees both numerical stability and that the models have less or equal dissipation than Vreman’s model, i.e., . The performance of the proposed models is successfully tested for decaying isotropic turbulence and a turbulent channel flow. The former test-case has revealed that the model constant, C s3pqr , should be higher than 0.458 to obtain the right amount of subgrid-scale dissipation, i.e., C s3pq = 0.572 (p = - 5/2), C s3pr = 0.709 (p = - 1), and C s3qr = 0.762 (p = 0).
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Wed, 06 Apr 2016 12:57:30 GMThttp://hdl.handle.net/2117/853022016-04-06T12:57:30ZTrias Miquel, Francesc XavierFolch, DavidGorobets, AndreiOliva Llena, AsensioDirect simulations of the incompressible Navier-Stokes equations are limited to relatively low-Reynolds numbers. Hence, dynamically less complex mathematical formulations are necessary for coarse-grain simulations. Eddy-viscosity models for large-eddy simulation is probably the most popular example thereof: they rely on differential operators that should properly detect different flow configurations (laminar and 2D flows, near-wall behavior, transitional regime, etc.). Most of them are based on the combination of invariants of a symmetric tensor that depends on the gradient of the resolved velocity field, . In this work, models are presented within a framework consisting of a 5D phase space of invariants. In this way, new models can be constructed by imposing appropriate restrictions in this space. For instance, considering the three invariants P GG T , Q GG T , and R GG T of the tensorGG T , and imposing the proper cubic near-wall behavior, i.e., , we deduce that the eddy-viscosity is given by . Moreover, only R GG T -dependent models, i.e., p > - 5/2, switch off for 2D flows. Finally, the model constant may be related with the Vreman’s model constant via ; this guarantees both numerical stability and that the models have less or equal dissipation than Vreman’s model, i.e., . The performance of the proposed models is successfully tested for decaying isotropic turbulence and a turbulent channel flow. The former test-case has revealed that the model constant, C s3pqr , should be higher than 0.458 to obtain the right amount of subgrid-scale dissipation, i.e., C s3pq = 0.572 (p = - 5/2), C s3pr = 0.709 (p = - 1), and C s3qr = 0.762 (p = 0).Hygrothermal analysis of characteristic public building rooms before energy efficient retrofitting solutions
http://hdl.handle.net/2117/84013
Hygrothermal analysis of characteristic public building rooms before energy efficient retrofitting solutions
Souaihi, Oussama; Capdevila, Roser; Lopez, Joan; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim
In the present paper, a modular, object-oriented and parallel methodology for the multiphysics simulation of buildings is presented. The whole building is modeled as a collection of basic elements (e.g., walls, rooms, outdoor, people, ventilation, solar radiation distributor, etc.). These elements can be modeled with different physical models and scales. A combined heat and moisture transfer model for the building envelopes and rooms have been implemented and validated with different benchmark cases. The simulation tool has been used within the framework of EU project for the simulation of hygrothermal behavior of various existing characteristic rooms inside three different public buildings (hospital, university and school) located in distinct locations of Europe (Spain, England and Sweden). Simulations allow the analysis of energy performance of different characteristic rooms of these demosites before the retrofitting solution of these buildings.
Tue, 08 Mar 2016 18:41:53 GMThttp://hdl.handle.net/2117/840132016-03-08T18:41:53ZSouaihi, OussamaCapdevila, RoserLopez, JoanLehmkuhl Barba, OriolRigola Serrano, JoaquimIn the present paper, a modular, object-oriented and parallel methodology for the multiphysics simulation of buildings is presented. The whole building is modeled as a collection of basic elements (e.g., walls, rooms, outdoor, people, ventilation, solar radiation distributor, etc.). These elements can be modeled with different physical models and scales. A combined heat and moisture transfer model for the building envelopes and rooms have been implemented and validated with different benchmark cases. The simulation tool has been used within the framework of EU project for the simulation of hygrothermal behavior of various existing characteristic rooms inside three different public buildings (hospital, university and school) located in distinct locations of Europe (Spain, England and Sweden). Simulations allow the analysis of energy performance of different characteristic rooms of these demosites before the retrofitting solution of these buildings.Parametric study of two-tank TES systems for CSP plants
http://hdl.handle.net/2117/83029
Parametric study of two-tank TES systems for CSP plants
Torras Ortiz, Santiago; Pérez Segarra, Carlos David; Rodríguez Pérez, Ivette María; Rigola Serrano, Joaquim; Oliva Llena, Asensio
The two-tank thermal energy storage (TES) system is the most used technology for storage in concentrating solar power (CSP) plants. This work focuses on a parametric study, which aims to identify the most important parameters on TES system, in order to improve the design and increase the performance of the plant. Three parameters have been considered: meteorological data, insulation thickness of the storage tank, and configuration of the foundation of the storage tank. The effect of each parameter is evaluated using numerical simulations based on a modular object-oriented methodology. The main issues related to the mathematical models and its numerical methodology are also presented in this paper.
Tue, 16 Feb 2016 16:10:22 GMThttp://hdl.handle.net/2117/830292016-02-16T16:10:22ZTorras Ortiz, SantiagoPérez Segarra, Carlos DavidRodríguez Pérez, Ivette MaríaRigola Serrano, JoaquimOliva Llena, AsensioThe two-tank thermal energy storage (TES) system is the most used technology for storage in concentrating solar power (CSP) plants. This work focuses on a parametric study, which aims to identify the most important parameters on TES system, in order to improve the design and increase the performance of the plant. Three parameters have been considered: meteorological data, insulation thickness of the storage tank, and configuration of the foundation of the storage tank. The effect of each parameter is evaluated using numerical simulations based on a modular object-oriented methodology. The main issues related to the mathematical models and its numerical methodology are also presented in this paper.