CTTC  Centre Tecnològic de la Transferència de Calor
http://hdl.handle.net/2117/3190
20170220T11:01:17Z

A levelset model for thermocapillary motion of deformable fluid particles
http://hdl.handle.net/2117/99861
A levelset model for thermocapillary motion of deformable fluid particles
Balcázar Arciniega, Néstor; Rigola Serrano, Joaquim; Castro González, Jesús; Oliva Llena, Asensio
A new levelset model is proposed for simulating immiscible thermocapillary flows with variable fluidproperty ratios at dynamically deformable interfaces. The Navier–Stokes equations coupled with the energy conservation equation are solved by means of a finitevolume/levelset approach, adapted to a multiple marker methodology in order to avoid the numerical coalescence of the fluid particles. The temperature field is coupled to the surface tension through an equation of state. Some numerical examples including thermocapillary driven convection in two superimposed fluid layers, and thermocapillary motion of single and multiple fluid particles are computed using the present method. These results are compared against analytical solutions and numerical results from the literature as validations of the proposed model.
20170123T13:58:57Z
Balcázar Arciniega, Néstor
Rigola Serrano, Joaquim
Castro González, Jesús
Oliva Llena, Asensio
A new levelset model is proposed for simulating immiscible thermocapillary flows with variable fluidproperty ratios at dynamically deformable interfaces. The Navier–Stokes equations coupled with the energy conservation equation are solved by means of a finitevolume/levelset approach, adapted to a multiple marker methodology in order to avoid the numerical coalescence of the fluid particles. The temperature field is coupled to the surface tension through an equation of state. Some numerical examples including thermocapillary driven convection in two superimposed fluid layers, and thermocapillary motion of single and multiple fluid particles are computed using the present method. These results are compared against analytical solutions and numerical results from the literature as validations of the proposed model.

Analysis and design of a drain water heat recovery storage unit based on PCM plates
http://hdl.handle.net/2117/99485
Analysis and design of a drain water heat recovery storage unit based on PCM plates
MoralesRuiz, S; Rigola Serrano, Joaquim; Oliet Casasayas, Carles; Oliva Llena, Asensio
This paper is focused on the detailed analysis of a PCM plate heat storage unit with a particular configuration, looking for the maximum contact area with the fluid (water) and the minimum volume to be used in a real household application. In that sense, a numerical study of the thermal and fluid dynamic behaviour of the water flow and the PCM meltingsolidification processes, together with the thermal behaviour of the solid elements of the unit, has been carried out. On the other hand, an experimental setup has been designed and built to validate the numerical model and characterise the performance of the heat storage unit. The purpose of the numerical and experimental study is to present a series of results to describe the heat storage unit performance in function of the time. Thus, after a preliminary design study three different cases have been simulated and tested. A 7.2% of discrepancy between numerical results and experimental data has been evaluated for the heat transfer. The PCM heat storage unit designed is capable to store approx. 75% of the thermal energy from the previous process wasted water heat, and recover part of it to supply around 50% of the thermal energy required to heat up the next process.
© 2016. This version is made available under the CCBYNCND 4.0 license http://creativecommons.org/licenses/byncnd/4.0/
20170117T13:51:44Z
MoralesRuiz, S
Rigola Serrano, Joaquim
Oliet Casasayas, Carles
Oliva Llena, Asensio
This paper is focused on the detailed analysis of a PCM plate heat storage unit with a particular configuration, looking for the maximum contact area with the fluid (water) and the minimum volume to be used in a real household application. In that sense, a numerical study of the thermal and fluid dynamic behaviour of the water flow and the PCM meltingsolidification processes, together with the thermal behaviour of the solid elements of the unit, has been carried out. On the other hand, an experimental setup has been designed and built to validate the numerical model and characterise the performance of the heat storage unit. The purpose of the numerical and experimental study is to present a series of results to describe the heat storage unit performance in function of the time. Thus, after a preliminary design study three different cases have been simulated and tested. A 7.2% of discrepancy between numerical results and experimental data has been evaluated for the heat transfer. The PCM heat storage unit designed is capable to store approx. 75% of the thermal energy from the previous process wasted water heat, and recover part of it to supply around 50% of the thermal energy required to heat up the next process.

Thermomechanical parametric analysis of packedbed thermocline energy storage tanks
http://hdl.handle.net/2117/99481
Thermomechanical parametric analysis of packedbed thermocline energy storage tanks
Ferreira González, Ignacio; Pérez Segarra, Carlos David; Lehmkuhl, Oriol; Torras, Santiago; Oliva Llena, Asensio
A packedbed thermocline tank represents a proved cheaper thermal energy storage for concentrated solar power plants compared with the commonlybuilt twotank system. However, its implementation has been stopped mainly due to the vessel’s thermal ratcheting concern, which would compromise its structural integrity. In order to have a better understanding of the commercial viability of thermocline approach, regarding energetic effectiveness and structural reliability, a new numerical simulation platform has been developed. The model dynamically solves and couples all the significant components of the subsystem, being able to evaluate its thermal and mechanical response over plant normal operation. The filler material is considered as a cohesionless bulk solid with thermal expansion. For the stresses on the tank wall the general thermoelastic theory is used. First, the numerical model is validated with the Solar One thermocline case, and then a parametric analysis is carried out by settling this storage technology in two real plants with a temperature rise of 100 °C and 275 °C. The numerical results show a better storage performance together with the lowest temperature difference, but both options achieve suitable structural factors of safety with a proper design.
© 2016. This version is made available under the CCBYNCND 4.0 license http://creativecommons.org/licenses/byncnd/4.0/
20170117T13:35:10Z
Ferreira González, Ignacio
Pérez Segarra, Carlos David
Lehmkuhl, Oriol
Torras, Santiago
Oliva Llena, Asensio
A packedbed thermocline tank represents a proved cheaper thermal energy storage for concentrated solar power plants compared with the commonlybuilt twotank system. However, its implementation has been stopped mainly due to the vessel’s thermal ratcheting concern, which would compromise its structural integrity. In order to have a better understanding of the commercial viability of thermocline approach, regarding energetic effectiveness and structural reliability, a new numerical simulation platform has been developed. The model dynamically solves and couples all the significant components of the subsystem, being able to evaluate its thermal and mechanical response over plant normal operation. The filler material is considered as a cohesionless bulk solid with thermal expansion. For the stresses on the tank wall the general thermoelastic theory is used. First, the numerical model is validated with the Solar One thermocline case, and then a parametric analysis is carried out by settling this storage technology in two real plants with a temperature rise of 100 °C and 275 °C. The numerical results show a better storage performance together with the lowest temperature difference, but both options achieve suitable structural factors of safety with a proper design.

Numerical analysis of conservative unstructured discretisations for low Mach flows
http://hdl.handle.net/2117/99477
Numerical analysis of conservative unstructured discretisations for low Mach flows
Ventosa Molina, Jordi; Chiva Segura, Jorge; Lehmkuhl, Oriol; Muela Castro, Jordi; Pérez Segarra, Carlos David; Oliva Llena, Asensio
Unstructured meshes allow easily representing complex geometries and to refine in regions of interest without adding control volumes in unnecessary regions.
However, numerical schemes used on unstructured grids have to be properly defined in order to minimise numerical errors.
An assessment of a lowMach algorithm for laminar and turbulent flows on unstructured meshes using collocated and staggered formulations is presented. For staggered formulations using cell centred velocity reconstructions the standard firstorder method is shown to be inaccurate in low Mach flows on unstructured grids. A recently proposed least squares procedure for incompressible flows is extended to the low Mach regime and shown to significantly improve the behaviour of the algorithm.
Regarding collocated discretisations, the oddeven pressure decoupling is handled through a kinetic energy conserving flux interpolation scheme. This approach is shown to efficiently handle variabledensity flows.
Besides, different face interpolations schemes for unstructured meshes are analysed.
A kinetic energy preserving scheme is applied to the momentum equations, namely the SymmetryPreserving (SP) scheme. Furthermore, a new approach to define the farneighbouring nodes of the QUICK scheme is presented and analysed. The method is suitable for both structured and unstructured grids, either uniform or not.
The proposed algorithm and the spatial schemes are assessed against a function reconstruction, a differentially heated cavity and a turbulent selfigniting diffusion flame. It is shown that the proposed algorithm accurately represents unsteady variabledensity flows. Furthermore, the QUICK schemes shows close to second order behaviour on unstructured meshes and the SP is reliably used in all computations.
This article may be used for noncommercial purposes in accordance with Wiley Terms and Conditions for SelfArchiving. https://authorservices.wiley.com/authorresources/JournalAuthors/licensingandopenaccess/openaccess/selfarchiving.html
20170117T13:20:41Z
Ventosa Molina, Jordi
Chiva Segura, Jorge
Lehmkuhl, Oriol
Muela Castro, Jordi
Pérez Segarra, Carlos David
Oliva Llena, Asensio
Unstructured meshes allow easily representing complex geometries and to refine in regions of interest without adding control volumes in unnecessary regions.
However, numerical schemes used on unstructured grids have to be properly defined in order to minimise numerical errors.
An assessment of a lowMach algorithm for laminar and turbulent flows on unstructured meshes using collocated and staggered formulations is presented. For staggered formulations using cell centred velocity reconstructions the standard firstorder method is shown to be inaccurate in low Mach flows on unstructured grids. A recently proposed least squares procedure for incompressible flows is extended to the low Mach regime and shown to significantly improve the behaviour of the algorithm.
Regarding collocated discretisations, the oddeven pressure decoupling is handled through a kinetic energy conserving flux interpolation scheme. This approach is shown to efficiently handle variabledensity flows.
Besides, different face interpolations schemes for unstructured meshes are analysed.
A kinetic energy preserving scheme is applied to the momentum equations, namely the SymmetryPreserving (SP) scheme. Furthermore, a new approach to define the farneighbouring nodes of the QUICK scheme is presented and analysed. The method is suitable for both structured and unstructured grids, either uniform or not.
The proposed algorithm and the spatial schemes are assessed against a function reconstruction, a differentially heated cavity and a turbulent selfigniting diffusion flame. It is shown that the proposed algorithm accurately represents unsteady variabledensity flows. Furthermore, the QUICK schemes shows close to second order behaviour on unstructured meshes and the SP is reliably used in all computations.

Parallel load balancing strategy for VolumeofFluid methods on 3D unstructured meshes
http://hdl.handle.net/2117/97703
Parallel load balancing strategy for VolumeofFluid methods on 3D unstructured meshes
Jofre Cruanyes, Lluís; Borrell Pol, Ricard; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
l VolumeofFluid (VOF) is one of the methods of choice to reproduce the interface motion in the simulation of multifluid flows. One of its main strengths is its accuracy in capturing sharp interface geometries, although requiring for it a number of geometric calculations. Under these circumstances, achieving parallel performance on current supercomputers is a must. The main obstacle for the parallelization is that the computing costs are concentrated only in the discrete elements that lie on the interface between fluids. Consequently, if the interface is not homogeneously distributed throughout the domain, standard domain decomposition (DD) strategies lead to imbalanced workload distributions. In this paper, we present a new parallelization strategy for general unstructured VOF solvers, based on a dynamic load balancing process complementary to the underlying DD. Its parallel efficiency has been analyzed and compared to the DD one using up to 1024 CPUcores on an Intel SandyBridge based supercomputer. The results obtained on the solution of several artificially generated test cases show a speedup of up to similar to 12x with respect to the standard DD, depending on the interface size, the initial distribution and the number of parallel processes engaged. Moreover, the new parallelization strategy presented is of general purpose, therefore, it could be used to parallelize any VOF solver without requiring changes on the coupled flow solver. Finally, note that although designed for the VOF method, our approach could be easily adapted to other interfacecapturing methods, such as the LevelSet, which may present similar workload imbalances. (C) 2014 Elsevier Inc. Allrights reserved.
© 2016. This version is made available under the CCBYNCND 4.0 license http://creativecommons.org/licenses/byncnd/4.0/
20161202T13:23:56Z
Jofre Cruanyes, Lluís
Borrell Pol, Ricard
Lehmkuhl Barba, Oriol
Oliva Llena, Asensio
l VolumeofFluid (VOF) is one of the methods of choice to reproduce the interface motion in the simulation of multifluid flows. One of its main strengths is its accuracy in capturing sharp interface geometries, although requiring for it a number of geometric calculations. Under these circumstances, achieving parallel performance on current supercomputers is a must. The main obstacle for the parallelization is that the computing costs are concentrated only in the discrete elements that lie on the interface between fluids. Consequently, if the interface is not homogeneously distributed throughout the domain, standard domain decomposition (DD) strategies lead to imbalanced workload distributions. In this paper, we present a new parallelization strategy for general unstructured VOF solvers, based on a dynamic load balancing process complementary to the underlying DD. Its parallel efficiency has been analyzed and compared to the DD one using up to 1024 CPUcores on an Intel SandyBridge based supercomputer. The results obtained on the solution of several artificially generated test cases show a speedup of up to similar to 12x with respect to the standard DD, depending on the interface size, the initial distribution and the number of parallel processes engaged. Moreover, the new parallelization strategy presented is of general purpose, therefore, it could be used to parallelize any VOF solver without requiring changes on the coupled flow solver. Finally, note that although designed for the VOF method, our approach could be easily adapted to other interfacecapturing methods, such as the LevelSet, which may present similar workload imbalances. (C) 2014 Elsevier Inc. Allrights reserved.

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 sandgrain 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.
20161130T13:51:35Z
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 sandgrain 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.

A new statistical model for subgrid dispersion in large eddy simulations of particleladen flows
http://hdl.handle.net/2117/97201
A new statistical model for subgrid dispersion in large eddy simulations of particleladen 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 particleladen 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/10.1088/17426596/745/3/032115
20161124T16:18:01Z
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 particleladen 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 semiimplicit methods for simulation of biomechanical fluidstructure interaction problems
http://hdl.handle.net/2117/97189
Partitioned semiimplicit methods for simulation of biomechanical fluidstructure interaction problems
Naseri, Alireza; Lehmkuhl Barba, Oriol; González Acedo, Ignacio; Oliva Llena, Asensio
This paper represents numerical simulation of fluidstructure interaction (FSI) system involving an
incompressible viscous fluid and a lightweight elastic structure. We follow a semiimplicit approach in which we
implicitly couple the addedmass 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 fixedpoint method with different static and dynamic relaxation,
as well as NewtonKrylov method with approximated Jacobian. Numerical tests are conducted in the context of a
biomechanical problem. Results indicate that the NewtonKrylov solver outperforms fixed point ones while introducing
more complexity to the problem due to the evaluation of the Jacobian. Fixedpoint 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/10.1088/17426596/745/3/032020.
20161124T14:59:40Z
Naseri, Alireza
Lehmkuhl Barba, Oriol
González Acedo, Ignacio
Oliva Llena, Asensio
This paper represents numerical simulation of fluidstructure interaction (FSI) system involving an
incompressible viscous fluid and a lightweight elastic structure. We follow a semiimplicit approach in which we
implicitly couple the addedmass 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 fixedpoint method with different static and dynamic relaxation,
as well as NewtonKrylov method with approximated Jacobian. Numerical tests are conducted in the context of a
biomechanical problem. Results indicate that the NewtonKrylov solver outperforms fixed point ones while introducing
more complexity to the problem due to the evaluation of the Jacobian. Fixedpoint solver with Aitken's relaxation
method also proved to be a simple, yet efficient method for FSI simulations.

A levelset method for thermal motion of bubbles and droplets
http://hdl.handle.net/2117/96631
A levelset method for thermal motion of bubbles and droplets
Balcázar Arciniega, Néstor; Oliva Llena, Asensio; Rigola Serrano, Joaquim
A conservative levelset model for direct simulation of twophase flows with thermocapillary effects at dynamically deformable interface is presented. The NavierStokes equations coupled with the energy conservation equation are solved by means of a finitevolume/levelset 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.
20161114T15:25:45Z
Balcázar Arciniega, Néstor
Oliva Llena, Asensio
Rigola Serrano, Joaquim
A conservative levelset model for direct simulation of twophase flows with thermocapillary effects at dynamically deformable interface is presented. The NavierStokes equations coupled with the energy conservation equation are solved by means of a finitevolume/levelset 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 threedimensional 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.
20161114T15:20:51Z
Bartrons Casademont, Eduard
Pérez Segarra, Carlos David
Oliet Casasayas, Carles
A threedimensional 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.