Ponències/Comunicacions de congressos
http://hdl.handle.net/2117/3992
2017-03-26T09:35:43ZNew parallel method for adjacent disconnected unstructured 3D meshes
http://hdl.handle.net/2117/102889
New parallel method for adjacent disconnected unstructured 3D meshes
Muela Castro, Jordi; Martínez Valdivieso, Daniel; Lehmkuhl Barba, Oriol; Pérez Segarra, Carlos David; Oliva Llena, Asensio
A new parallel method for simulations with non-overlapping disconnected
mesh domains but adjacent boundaries is presented and studied. This technique allows simulations using 3D unstructured meshes that are independent.
2017-03-24T18:35:46ZMuela Castro, JordiMartínez Valdivieso, DanielLehmkuhl Barba, OriolPérez Segarra, Carlos DavidOliva Llena, AsensioA new parallel method for simulations with non-overlapping disconnected
mesh domains but adjacent boundaries is presented and studied. This technique allows simulations using 3D unstructured meshes that are independent.Numerical simulation of roughness effects on the flow past a circular cylinder
http://hdl.handle.net/2117/97516
Numerical simulation of roughness effects on the flow past a circular cylinder
Rodríguez Pérez, Ivette María; Lehmkuhl, Oriol; Piomelli, Ugo; Chiva Segura, Jorge; Borrell, Ricard; Oliva Llena, Asensio
In the present work large eddy simulations of the flow past a rough cylinder are performed at a Reynolds number of Re = 4.2 × 105 and an equivalent sand-grain surface roughness height ks = 0.02D. 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 those of the smooth cylinder. It is shown that surface roughness triggers the transition to turbulence in the boundary layer, thus leading to an early separation caused by the increased drag and momentum deficit. Thus, the drag coefficient increases up to CD 1.122 (if compared to the smooth cylinder it should be about CD 0.3 - 0.5).
The wake topology also changes and resembles more the subcritical wake observed for the smooth cylinder at lower Reynolds numbers than the expected critical wake at this Reynolds number.
2016-11-30T13:51:35ZRodríguez Pérez, Ivette MaríaLehmkuhl, OriolPiomelli, UgoChiva Segura, JorgeBorrell, RicardOliva Llena, AsensioIn the present work large eddy simulations of the flow past a rough cylinder are performed at a Reynolds number of Re = 4.2 × 105 and an equivalent sand-grain surface roughness height ks = 0.02D. 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 those of the smooth cylinder. It is shown that surface roughness triggers the transition to turbulence in the boundary layer, thus leading to an early separation caused by the increased drag and momentum deficit. Thus, the drag coefficient increases up to CD 1.122 (if compared to the smooth cylinder it should be about CD 0.3 - 0.5).
The wake topology also changes and resembles more the subcritical wake observed for the smooth cylinder at lower Reynolds numbers than the expected critical wake at this Reynolds number.Design of a test bench for measuring friction force in a piston-cylinder system
http://hdl.handle.net/2117/97237
Design of a test bench for measuring friction force in a piston-cylinder system
Buj Corral, Irene; Zayas Figueras, Enrique Ernesto; Álvarez Flórez, Jesús Andrés; Gutiérrez González, Ernesto
In the present work, design of a first approach of a test bench prototype for measuring friction in a piston-cylinder system is presented. The bench consists of a motor, belt and pulley transmission, crank mechanism, a piston, a cylinder and a lubrication system. Friction will be determined by means of strain gages placed on the connecting rod of the mechanism. The bench also includes a phonic wheel for acquiring angular speed and angular position signals of the crank. In future research, friction will be studied for different surface finishes obtained by means of honing and plateau honing. Honing processes provide a crosshatch pattern that holds oil and helps lubrication of piston and rings. Honing conditions will be selected with the goal of minimizing friction. Friction is directly related to energy consumption of an engine and, thus, to its environmental impact. Keywords: test bench, friction, piston-cylinder system, honing, roughness.
2016-11-25T11:11:12ZBuj Corral, IreneZayas Figueras, Enrique ErnestoÁlvarez Flórez, Jesús AndrésGutiérrez González, ErnestoIn the present work, design of a first approach of a test bench prototype for measuring friction in a piston-cylinder system is presented. The bench consists of a motor, belt and pulley transmission, crank mechanism, a piston, a cylinder and a lubrication system. Friction will be determined by means of strain gages placed on the connecting rod of the mechanism. The bench also includes a phonic wheel for acquiring angular speed and angular position signals of the crank. In future research, friction will be studied for different surface finishes obtained by means of honing and plateau honing. Honing processes provide a crosshatch pattern that holds oil and helps lubrication of piston and rings. Honing conditions will be selected with the goal of minimizing friction. Friction is directly related to energy consumption of an engine and, thus, to its environmental impact. Keywords: test bench, friction, piston-cylinder system, honing, roughness.A new statistical model for subgrid dispersion in large eddy simulations of particle-laden flows
http://hdl.handle.net/2117/97201
A new statistical model for subgrid dispersion in large eddy simulations of particle-laden flows
Muela Castro, Jordi; Lehmkuhl Barba, Oriol; Pérez Segarra, Carlos David; Oliva Llena, Asensio
Dispersed multiphase turbulent flows are present in many industrial and commercial applications like
internal combustion engines, turbofans, dispersion of contaminants, steam turbines, etc. Therefore, there is a clear
interest in the development of models and numerical tools capable of performing detailed and reliable simulations
about these kind of flows. Large Eddy Simulations offer good accuracy and reliable results together with reasonable
computational requirements, making it a really interesting method to develop numerical tools for particle-laden turbulent
flows. Nonetheless, in multiphase dispersed flows additional difficulties arises in LES, since the effect of the unresolved
scales of the continuous phase over the dispersed phase is lost due to the filtering procedure. In order to solve this
issue a model able to reconstruct the subgrid velocity seen by the particles is required. In this work a new model for
the reconstruction of the subgrid scale effects over the dispersed phase is presented and assessed. This innovative
methodology is based in the reconstruction of statistics via Probability Density Functions (PDFs).
This article is published under a CC BY licence. The Version of Record is available online at: http.//dx.doi.org/10.1088/1742-6596/745/3/032115
2016-11-24T16:18:01ZMuela Castro, JordiLehmkuhl Barba, OriolPérez Segarra, Carlos DavidOliva Llena, AsensioDispersed multiphase turbulent flows are present in many industrial and commercial applications like
internal combustion engines, turbofans, dispersion of contaminants, steam turbines, etc. Therefore, there is a clear
interest in the development of models and numerical tools capable of performing detailed and reliable simulations
about these kind of flows. Large Eddy Simulations offer good accuracy and reliable results together with reasonable
computational requirements, making it a really interesting method to develop numerical tools for particle-laden turbulent
flows. Nonetheless, in multiphase dispersed flows additional difficulties arises in LES, since the effect of the unresolved
scales of the continuous phase over the dispersed phase is lost due to the filtering procedure. In order to solve this
issue a model able to reconstruct the subgrid velocity seen by the particles is required. In this work a new model for
the reconstruction of the subgrid scale effects over the dispersed phase is presented and assessed. This innovative
methodology is based in the reconstruction of statistics via Probability Density Functions (PDFs).Partitioned semi-implicit methods for simulation of biomechanical fluid-structure interaction problems
http://hdl.handle.net/2117/97189
Partitioned semi-implicit methods for simulation of biomechanical fluid-structure interaction problems
Naseri, Alireza; Lehmkuhl Barba, Oriol; González Acedo, Ignacio; Oliva Llena, Asensio
This paper represents numerical simulation of fluid-structure interaction (FSI) system involving an
incompressible viscous fluid and a lightweight elastic structure. We follow a semi-implicit approach in which we
implicitly couple the added-mass term (pressure stress) of the fluid to the structure, while other terms are coupled
explicitly. This significantly reduces the computational cost of the simulations while showing adequate stability.
Several coupling schemes are tested including fixed-point method with different static and dynamic relaxation,
as well as Newton-Krylov method with approximated Jacobian. Numerical tests are conducted in the context of a
biomechanical problem. Results indicate that the Newton-Krylov solver outperforms fixed point ones while introducing
more complexity to the problem due to the evaluation of the Jacobian. Fixed-point solver with Aitken's relaxation
method also proved to be a simple, yet efficient method for FSI simulations.
This article is published under a CC BY licence. The Version of Record is available online at: http://dx.doi.org/10.1088/1742-6596/745/3/032020.
2016-11-24T14:59:40ZNaseri, AlirezaLehmkuhl Barba, OriolGonzález Acedo, IgnacioOliva Llena, AsensioThis paper represents numerical simulation of fluid-structure interaction (FSI) system involving an
incompressible viscous fluid and a lightweight elastic structure. We follow a semi-implicit approach in which we
implicitly couple the added-mass term (pressure stress) of the fluid to the structure, while other terms are coupled
explicitly. This significantly reduces the computational cost of the simulations while showing adequate stability.
Several coupling schemes are tested including fixed-point method with different static and dynamic relaxation,
as well as Newton-Krylov method with approximated Jacobian. Numerical tests are conducted in the context of a
biomechanical problem. Results indicate that the Newton-Krylov solver outperforms fixed point ones while introducing
more complexity to the problem due to the evaluation of the Jacobian. Fixed-point solver with Aitken's relaxation
method also proved to be a simple, yet efficient method for FSI simulations.A level-set method for thermal motion of bubbles and droplets
http://hdl.handle.net/2117/96631
A level-set method for thermal motion of bubbles and droplets
Balcázar Arciniega, Néstor; Oliva Llena, Asensio; Rigola Serrano, Joaquim
A conservative level-set model for direct simulation of two-phase flows with thermocapillary effects at dynamically deformable interface is presented. The Navier-Stokes equations coupled with the energy conservation equation are solved by means of a finite-volume/level-set method. Some numerical examples including thermocapillary motion of single and multiple fluid particles are computed by means of the present method. The results are compared with analytical solutions and numerical results from the literature as validations of the proposed model.
Published under licence in Journal of Physics: Conference Series 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.
2016-11-14T15:25:45ZBalcázar Arciniega, NéstorOliva Llena, AsensioRigola Serrano, JoaquimA conservative level-set model for direct simulation of two-phase flows with thermocapillary effects at dynamically deformable interface is presented. The Navier-Stokes equations coupled with the energy conservation equation are solved by means of a finite-volume/level-set method. Some numerical examples including thermocapillary motion of single and multiple fluid particles are computed by means of the present method. The results are compared with analytical solutions and numerical results from the literature as validations of the proposed model.Frost formation: optimizing solutions under a finite volume approach
http://hdl.handle.net/2117/96630
Frost formation: optimizing solutions under a finite volume approach
Bartrons Casademont, Eduard; Pérez Segarra, Carlos David; Oliet Casasayas, Carles
A three-dimensional transient formulation of the frost formation process is developed by means of a finite volume approach. Emphasis is put on the frost surface boundary condition as well as the wide range of empirical correlations related to the thermophysical and transport properties of frost. A study of the numerical solution is
made, establishing the parameters that ensure grid independence. Attention is given to the algorithm, the discretised equations and the code optimization through dynamic relaxation techniques. A critical analysis of four cases is carried out by comparing solutions of several empirical models against tested experiments. As a result, a discussion on the performance of such parameters is started and a proposal of the most suitable models is presented.
Published under licence in Journal of Physics: Conference Series 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.
2016-11-14T15:20:51ZBartrons Casademont, EduardPérez Segarra, Carlos DavidOliet Casasayas, CarlesA three-dimensional transient formulation of the frost formation process is developed by means of a finite volume approach. Emphasis is put on the frost surface boundary condition as well as the wide range of empirical correlations related to the thermophysical and transport properties of frost. A study of the numerical solution is
made, establishing the parameters that ensure grid independence. Attention is given to the algorithm, the discretised equations and the code optimization through dynamic relaxation techniques. A critical analysis of four cases is carried out by comparing solutions of several empirical models against tested experiments. As a result, a discussion on the performance of such parameters is started and a proposal of the most suitable models is presented.Numerical simulations of conjugate convection combined with surface thermal radiation using an Immersed-Boundary Method
http://hdl.handle.net/2117/96629
Numerical simulations of conjugate convection combined with surface thermal radiation using an Immersed-Boundary Method
Favre Samarra, Federico; Colomer Rey, Guillem; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
Dynamic and thermal interaction problems involving fluids and solids were studied through a finite volume based Navier-Stokes solver, combined with immersed-boundary techniques and the net radiation method. Source terms were included in the momentum and energy equations to enforce the non-slip condition and the conjugate boundary condition including the radiative heat exchange. Code validation was performed through the simulation of two cases from the literature: conjugate natural convection in a square cavity with a conducting side wall; and a cubical cavity with conducting walls and a heat source. The accuracy of the methodology and the validation of the inclusion of moving bodies into the simulation was performed via a theoretical case.
Published under licence in Journal of Physics: Conference Series 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.
2016-11-14T15:04:32ZFavre Samarra, FedericoColomer Rey, GuillemLehmkuhl Barba, OriolOliva Llena, AsensioDynamic and thermal interaction problems involving fluids and solids were studied through a finite volume based Navier-Stokes solver, combined with immersed-boundary techniques and the net radiation method. Source terms were included in the momentum and energy equations to enforce the non-slip condition and the conjugate boundary condition including the radiative heat exchange. Code validation was performed through the simulation of two cases from the literature: conjugate natural convection in a square cavity with a conducting side wall; and a cubical cavity with conducting walls and a heat source. The accuracy of the methodology and the validation of the inclusion of moving bodies into the simulation was performed via a theoretical case.On the solution of the full three-dimensional Taylor bubble problem by using a coupled Conservative Level Set - Moving Mesh method
http://hdl.handle.net/2117/96626
On the solution of the full three-dimensional Taylor bubble problem by using a coupled Conservative Level Set - Moving Mesh method
Gutiérrez Álvarez, Enrique; Balcázar Arciniega, Néstor; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
The challenging problem of the full three-dimensional Taylor bubble has been addressed by using a Conservative Level Set method in order to deal with the multiphase flow. A moving mesh is used, aiming to optimize the simulation domain. The mesh is moved as the bubble rises, so the region of study can be limited to the surroundings of the bubble, notably reducing the domain's size. This saving in the computational resources facilitates to face the Taylor bubble problem without the axisymmetric assumption. By doing so, a detailed description of the fluid field is provided, comparing the results against numerical and experimental data.
Published under licence in Journal of Physics: Conference Series 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.
2016-11-14T14:48:19ZGutiérrez Álvarez, EnriqueBalcázar Arciniega, NéstorLehmkuhl Barba, OriolOliva Llena, AsensioThe challenging problem of the full three-dimensional Taylor bubble has been addressed by using a Conservative Level Set method in order to deal with the multiphase flow. A moving mesh is used, aiming to optimize the simulation domain. The mesh is moved as the bubble rises, so the region of study can be limited to the surroundings of the bubble, notably reducing the domain's size. This saving in the computational resources facilitates to face the Taylor bubble problem without the axisymmetric assumption. By doing so, a detailed description of the fluid field is provided, comparing the results against numerical and experimental data.New subgrid-scale models for large-eddy simulation of Rayleigh-Bénard convection
http://hdl.handle.net/2117/96616
New subgrid-scale models for large-eddy simulation of Rayleigh-Bénard convection
Dabbagh, Firas; Trias Miquel, Francesc Xavier; Gorobets, Andrei; Oliva Llena, Asensio
At the crossroad between flow topology analysis and the theory of turbulence, a new eddy-viscosity model for Large-eddy simulation has been recently proposed by Trias et al.[PoF, 27, 065103 (2015)]. The S3PQR-model has the proper cubic near-wall behaviour and no intrinsic limitations for statistically inhomogeneous flows. In this work, the new model has been tested for an air turbulent Rayleigh-Benard convection in a rectangular cell of aspect ratio unity and n span-wise open-ended distance. To do so, direct numerical simulation has been carried out at two Rayleigh numbers Ra = 108 and 1010, to assess the model performance and investigate a priori the effect of the turbulent Prandtl number. Using an approximate formula based on the Taylor series expansion, the turbulent Prandtl number has been calculated and revealed a constant and Ra-independent value across the bulk region equals to 0.55. It is found that the turbulent components of eddy-viscosity and eddy-diffusivity are positively prevalent to maintain a turbulent wind essentially driven by the mean buoyant force at the sidewalls. On the other hand, the new eddy-viscosity model is preliminary tested for the case of Ra = 108 and showed overestimation of heat flux within the boundary layer but fairly good prediction of turbulent kinetics at this moderate turbulent flow.
Published under licence in Journal of Physics: Conference Series 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.
2016-11-14T13:32:43ZDabbagh, FirasTrias Miquel, Francesc XavierGorobets, AndreiOliva Llena, AsensioAt the crossroad between flow topology analysis and the theory of turbulence, a new eddy-viscosity model for Large-eddy simulation has been recently proposed by Trias et al.[PoF, 27, 065103 (2015)]. The S3PQR-model has the proper cubic near-wall behaviour and no intrinsic limitations for statistically inhomogeneous flows. In this work, the new model has been tested for an air turbulent Rayleigh-Benard convection in a rectangular cell of aspect ratio unity and n span-wise open-ended distance. To do so, direct numerical simulation has been carried out at two Rayleigh numbers Ra = 108 and 1010, to assess the model performance and investigate a priori the effect of the turbulent Prandtl number. Using an approximate formula based on the Taylor series expansion, the turbulent Prandtl number has been calculated and revealed a constant and Ra-independent value across the bulk region equals to 0.55. It is found that the turbulent components of eddy-viscosity and eddy-diffusivity are positively prevalent to maintain a turbulent wind essentially driven by the mean buoyant force at the sidewalls. On the other hand, the new eddy-viscosity model is preliminary tested for the case of Ra = 108 and showed overestimation of heat flux within the boundary layer but fairly good prediction of turbulent kinetics at this moderate turbulent flow.