Graphic summary
  • Show / hide key
  • Information


Scientific and technological production
  •  

1 to 50 of 132 results
  • Symmetry-preserving discretization of Navier-Stokes equations on collocated unstructured meshes

     Trias Miquel, Francesc Xavier; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio; Perez Segarra, Carlos David; Verstappen, R.W.C.P.
    Journal of computational physics
    Date of publication: 2014-02-01
    Journal article

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    A fully-conservative discretization is presented in this paper. The same principles followed by Verstappen and Veldman (2003) are generalized for unstructured meshes. Here, a collocated-mesh scheme is preferred over a staggered one due to its simpler form for such meshes. The basic idea behind this approach remains the same: mimicking the crucial symmetry properties of the underlying differential operators, i.e., the convective operator is approximated by a skew-symmetric matrix and the diffusive operator by a symmetric, positive-definite matrix. A novel approach to eliminate the checkerboard spurious modes without introducing any non-physical dissipation is proposed. To do so, a fully-conservative regularization of the convective term is used. The supraconvergence of the method is numerically showed and the treatment of boundary conditions is discussed. Finally, the new discretization method is successfully tested for a buoyancy-driven turbulent flow in a differentially heated cavity.

  • Limits of the Oberbeck¿Boussinesq approximation in a tall differentially heated cavity filled with water

     Kizildag, Deniz; Rodriguez Pérez, Ivette Maria; Oliva Llena, Asensio; Lehmkuhl Barba, Oriol
    International journal of heat and mass transfer
    Date of publication: 2014-01-01
    Journal article

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    The present work assesses the limits of the Oberbeck¿Boussinesq (OB) approximation for the resolution of turbulent fluid flow and heat transfer inside a tall differentially heated cavity of aspect ratio G = 6.67 filled with water (Pr = 3.27, Ra = 2.12e11). The cavity models the integrated solar collector-storage element installed on an advanced façade. The implications of the Oberbeck¿Boussinesq approximation is submitted to investigation by means of direct numerical simulations (DNS) carried out for a wide range of temperature differences. Non-Oberbeck¿Boussinesq (NOB) effects are found to be relevant, especially beyond the temperature difference of 30 °C, in the estimation of heat transfer, stratification, and flow configuration.

  • Low-frequency unsteadiness in the vortex formation region of a circular cylinder

     Lehmkuhl Barba, Oriol; Rodriguez Pérez, Ivette Maria; Borrell Pol, Ricard; Oliva Llena, Asensio
    Physics of fluids
    Date of publication: 2013-08-23
    Journal article

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    The presence of low-frequency fluctuations in the wake of bluff bodies have been observed in several investigations. Even though the flow past a circular cylinder at Re = 3900 (Re = UrefD/¿) has been the object of several experimental and numerical investigations, there is a large scattering in the average statistics in the near wake. In the present work, the flow dynamics of the near wake region behind a circular cylinder has been investigated by means of direct numerical simulations and statistics have been computed for more than 858 shedding cycles. The analysis of instantaneous velocity signals of several probes located in the vortex formation region, point out the existence of a low-frequency fluctuation at the non-dimensional frequency of fm = 0.0064. This large-scale almost periodic motion seems to be related with the modulation of the recirculation bubble which causes its shrinking and enlargement over the time. Two different configurations have been identified: (i) a high-energy mode with larger fluctuations in the shear-layer and in the vortex formation region (Mode H) and (ii) a low-energy mode with weaker fluctuations in the shear layer (Mode L). The influence of such a low-frequency in the wake topology has been studied not only by means of the phase-average flow field for each mode, but also by the analysis of the time-average first- and second-order statistics of each wake mode. The results are compared with the long-term averaged solution and with results in the existing literature.

  • On the large-eddy simulations for the flow around aerodynamic profiles using unstructured grids

     Lehmkuhl Barba, Oriol; Rodriguez Pérez, Ivette Maria; Baez Vidal, Aleix; Oliva Llena, Asensio; Perez Segarra, Carlos David
    Computers and fluids
    Date of publication: 2013-09-15
    Journal article

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    This paper investigates the capabilities of two subgrid-scale (SGS) models suitable for unstructured grids for predicting the complex flow in transitional separated bubbles. The flow over a NACA 0012 airfoil at Reynolds number Re = 5e4 and angles of attack (AOA) AOA = 5° and 8° is here considered. The SGS models investigated are: the wall-adapting eddy viscosity model within a variational multiscale method (VMS-WALE) and the QR eddy-viscosity model. Both are well suited for large-eddy simulations (LES) in complex geometries with unstructured grids. The models are assessed and compared to the results of direct numerical simulations (DNS) on the basis of first and second order statistics. Based on the good results obtained, specially with the VMS-WALE model, challenging simulations at high Reynolds numbers and various AOA are also performed. It has been found that predictions of the lift and drag coefficients agree reasonably well with experimental data.

  • Flow dynamics in the turbulent wake of a sphere at sub-critical Reynolds numbers

     Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Oliva Llena, Asensio
    Computers and fluids
    Date of publication: 2013-07-10
    Journal article

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    Direct numerical simulations of the flow over a sphere have been performed. The computations have been carried out in the sub-critical regime at Re = 3700 and Re = 10,000 (based on the free-stream velocity and the sphere diameter). A parallel unstructured symmetry-preserving formulation has been used for simulating the flow. Computations have been carried out on unstructured grids obtained by the constant-step rotation about the axis of a two-dimensional grid. With this discretisation, the Poisson equation has been solved by means of a Fourier diagonalization method. Particular attention has been devoted to investigate the shear-layer instabilities and its influence in the vortical structures, as well as the wake configuration. The main features of the flow including power spectra of a set of selected monitoring probes at different positions have been described and discussed in detail. Detailed information about turbulent statistics have also been provided.

  • Access to the full text
    Modular object-oriented methodology for the resolution of molten salt storage tanks for CSP plants  Open access

     Rodriguez Pérez, Ivette Maria; Perez Segarra, Carlos David; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
    Applied energy
    Date of publication: 2013-09
    Journal article

    Read the abstract Read the abstract Access to the full text Access to the full text Open in new window  Share Reference managers Reference managers Open in new window

    Two-tank molten salt storages are the most widespread thermal energy storage technology within concentrated solar power plants. In spite of this, there are design aspects such as thermal losses control, optimisation of the storage or how these devices scale up with the increase in power capacity of the plant which still should be considered. In this sense, numerical modelling of these systems can be a powerful tool for reducing their cost. The present work aims at modelling molten salt tanks by proposing a parallel modular object-oriented methodology which considers the different elements of the storage (e.g. tank walls, insulation material, tank foundation, molten salt storage media, etc.) as independent systems. Each of these elements can be solved independently and using different levels of modelling (from global to fully three-dimensional models), while at the same time they are linked to each other through their boundary conditions. The mathematical models used, together with some illustrative examples of the application of the proposed methodology, are presented and discussed in detail.

    Two-tank molten salt storages are the most widespread thermal energy storage technology within concentrated solar power plants. In spite of this, there are design aspects such as thermal losses control, optimisation of the storage or how these devices scale up with the increase in power capacity of the plant which still should be considered. In this sense, numerical modelling of these systems can be a powerful tool for reducing their cost. The present work aims at modelling molten salt tanks by proposing a parallel modular object-oriented methodology which considers the different elements of the storage (e.g. tank walls, insulation material, tank foundation, molten salt storage media, etc.) as independent systems. Each of these elements can be solved independently and using different levels of modelling (from global to fully three-dimensional models), while at the same time they are linked to each other through their boundary conditions. The mathematical models used, together with some illustrative examples of the application of the proposed methodology, are presented and discussed in detail.

  • Direct numerical simulation of a NACA0012 in full stall

     Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Oliva Llena, Asensio
    International journal of heat and fluid flow
    Date of publication: 2013-10-15
    Journal article

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    This work aims at investigating the mechanisms of separation and the transition to turbulence in the separated shear-layer of aerodynamic profiles, while at the same time to gain insight into coherent structures formed in the separated zone at low-to-moderate Reynolds numbers. To do this, direct numerical simulations of the flow past a NACA0012 airfoil at Reynolds numbers Re = 50,000 (based on the free-stream velocity and the airfoil chord) and angles of attack AOA = 9.25 and AOA = 12 have been carried out. At low-to-moderate Reynolds numbers, NACA0012 exhibits a combination of leading-edge/trailing-edge stall which causes the massive separation of the flow on the suction side of the airfoil. The initially laminar shear layer undergoes transition to turbulence and vortices formed are shed forming a von Kármán like vortex street in the airfoil wake. The main characteristics of this flow together with its main features, including power spectra of a set of selected monitoring probes at different positions on the suction side and in the wake of the airfoil are provided and discussed in detail.

  • Parallel sweep-based preconditioner for the solution of the linear Boltzmann transport equation

     Borrell Pol, Ricard; Colomer Rey, Guillem; Lehmkuhl Barba, Oriol; Rodriguez Pérez, Ivette Maria; Oliva Llena, Asensio
    Computers and fluids
    Date of publication: 2013-12-15
    Journal article

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    The Boltzmann transport equation is solved in the context of radiative heat transfer, for an isotropically scattering medium with reflecting boundaries. Under these circumstances, the different ordinates of the angular flux are mutually coupled. We explore here the use of a parallel sweep-based block diagonal preconditioner as a complement of the GMRES solver on the solution of the discretization matrix (which includes all the inter-ordinate couplings). The validity of this approach, when compared to the standard source iteration scheme, is successfully assessed for a significant range of the coupling parameters.

  • Conservation properties of unstructured finite-volume mesh schemes for the Navier-Stokes equations

     Jofre Cruanyes, Lluís; Lehmkuhl Barba, Oriol; Ventosa Molina, Jordi; Trias Miquel, Francesc Xavier; Oliva Llena, Asensio
    Numerical heat transfer. Part B, fundamentals
    Date of publication: 2013-11-09
    Journal article

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    The Navier-Stokes equations describe fluid flow by conserving mass and momentum. There are two main mesh discretizations for the computation of these equations, the collocated and staggered schemes. Collocated schemes locate the velocity field at the same grid points as the pressure one, while staggered discretizations locate variables at different points within the mesh. One of the most important characteristic of the discretization schemes, aside from accuracy, is their capacity to discretely conserve kinetic energy, specially when solving turbulent flow. Hence, this work analyzes the accuracy and conservation properties of two particular collocated and staggered schemes by solving various problems.

  • Parallel adaptive mesh refinement simulation of the flow around a square cylinder at Re = 22000

     Antepara Zambrano, Oscar; Lehmkuhl Barba, Oriol; Chiva Segura, Jorge; Borrell, Ricard
    International Conference on Parallel Computational Fluid Dynamics
    Presentation's date: 2013-05-22
    Presentation of work at congresses

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    In this paper a parallel adaptive mesh refinement for LES simulation of turbulent flows is presented. The AMR scheme applies a cell- based refinement technique to get enough grid-resolution to solve the small scales structures, adapting the mesh according to physics- based refinement criteria. A flexible tree data structure is used to keeping track of the mesh adaptation and an edge-based data structure to save and search cell connectivity. The AMR framework is combined with parallel algorithms for partitioning and balancing of the computational mesh. Numerical results for turbulent flow around a square cylinder at Re = 22000 are compared to experimental data.

  • Parallelization strategy for the Volume-of-Fluid method on unstructured meshes

     Borrell, Ricard; Jofre Cruanyes, Lluís; Lehmkuhl Barba, Oriol; Castro Gonzalez, Jesus
    International Conference on Parallel Computational Fluid Dynamics
    Presentation of work at congresses

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    The Volume-of-Fluid (VOF) is one of the most widely used methods for interface tracking in the simulation of multi-fluid flows. The interface between different fluids is generated from the volume fraction scalar fields, which account for the ratio of volume of each fluid in each control volume. Then, an advection equation is solved to obtain the new distribution of the fluids after momentum is applied. Since this is a time-consuming process, parallelization techniques play an essential role. In the VOF approaches most of computing cost of the algorithm is concentrated in operations with the cells that form the interface, i.e. the cells in which coexist different fluids. When the interface is not homogeneously distributed throughout the domain, the standard domain decomposition strategy results in an unbalanced partition. A possible strategy to overcome this limitation is to adapt the domain decomposition to the interface distribution, however, this approach presents a number of drawbacks mainly related to the dynamic location of the interface. In this paper a new strategy, based in a load balancing process complementary to the domain decomposition, is presented with the aim to overcome the limitations of standard domain decomposition based approaches.

  • Numerical simulation tools for energy efficiency in buildings. HAM transfer in facades coupled with CFD models for air distribution

     Damle, Rashmin; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; Oliva Llena, Asensio
    REHVA World Congress
    Presentation's date: 2013-06
    Presentation of work at congresses

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    Buildings represent a major part of the world energy requirement. The simulation of combined heat, air and moisture (HAM) and pollutant transfer in this context is important to predict the indoor air quality, along with the thermal comfort. Moreover, it is important to have appropriate levels of indoor humidity along with the room temperature as movement of water vapor through the building envelope causes a lot of harm to the building structure and reduces the quality of its thermal insulation leading to higher energy demand. The knowledge of the peak loads, temperatures, humidity levels can help to optimize the building design and therefore results in energy efficient buildings. In this work a modular object-oriented building simulation tool (NEST), capable of coupling different levels of simulation models, allowing the simulation of heat, air, moisture distribution (multizone model, envelope model, room analysis and HVAC system) is presented. The modular approach gives flexibility of choosing a model for each element and to have different levels of modeling for different elements in the system. Special attention has been focused on: the large eddy simulation turbulence models used for the room air dynamics and pollutants distribution transport and high performance parallel software. Parallelization of the building simulation is necessary if some critical processes/zones need to be modeled with more detail for reducing computational time. The main focus of this article is to couple the HAM models for the building envelope with CFD HT models with heat, moisture and pollutant transfer models for room airflow.

  • Numerical simulation and experimental validation of sensible heat accumulators oriented to zero energy buildings

     Torras, Santiago; Oliet Casasayas, Carles; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim
    REHVA World Congress
    Presentation's date: 2013-06
    Presentation of work at congresses

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    The sensible heat accumulation is an efficient and low-cost way of storing thermal energy for its direct or indirect reutilization in typical building processes as space heating and sanitary hot water generation. The authors are developing both numerical and experimental tools for the study and optimisation of this kind of systems, focusing on the analysis of a specific sensible heat accumulator based on a cylindrical tank with an internal coiled pipe. The numerical simulation has been performed using a high-level platform that links two codes to solve the system. The fluid inside the tank is solved with a CFD&HT (Computational Fluid Dynamics & Heat Transfer) software called TermoFluids and the fluid flow inside the pipe is solved considering a quasi-homogenous fully-implicit one-dimensional model, where the governing equations are discretized along the whole tube domain. The resolution of the pipe wall in a detailed way couples both fluid solvers. On the other hand, an experimental infrastructure has been developed for the analysis of the system, which has been instrumented to provide detailed information of its heat storage capacity and temperature map. Several temperature sensors are incorporated in the heat accumulator at different heights and radius inside the tank. For the internal flow, the mass flow rate is measured, as well as the inlet and outlet temperatures. Different internal flow rates and operational temperatures have been studied both numerically and experimentally. From the results obtained it can be said that the device shows interesting heat storage capacities, while the numerical platform shows promising comparison results against the experiments.

  • On the large-eddy simulations of the flow past a cylinder at critical Reynolds numbers

     Lehmkuhl Barba, Oriol; Rodriguez Pérez, Ivette Maria; Chiva Segura, Jorge; Borrell Pol, Ricard
    ERCOFTAC Workshop on Direct and Large-Eddy Simulation
    Presentation's date: 2013-04-03
    Presentation of work at congresses

    View View Open in new window  Share Reference managers Reference managers Open in new window

  • Flow past a NACA0012 airfoil: from laminar separation bubbles to fully stalled regime

     Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Oliva Llena, Asensio
    ERCOFTAC Workshop on Direct and Large-Eddy Simulation
    Presentation's date: 2013-04-04
    Presentation of work at congresses

    View View Open in new window  Share Reference managers Reference managers Open in new window

  • A new thermocline-PCM thermal storage concept for CSP plants. Numerical analysis and perspectives

     Galione Klot, Pedro Andres; Perez Segarra, Carlos David; Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim
    Solar Power and Chemical Energy Systems Conference
    Presentation's date: 2013-09
    Presentation of work at congresses

    Read the abstract Read the abstract  Share Reference managers Reference managers Open in new window

    Thermocline storage concept has been considered for more than a decade as a possible solution to reduce the huge cost of the storage system in CSP plants. However, one of the drawbacks of this concept is the decrease in its performance throughout the time. The objective of this paper is to present a new thermocline-PCM storage concept which aims at circumventing this issue. The concept proposed is built of different solid filler materials and encapsulated PCMs combined into a multi-layer storage tank with molten salt as heat transfer fluid. The performance evaluation of each of the prototypes proposed is virtually tested by means of a detailed numerical methodology which considers the heat transfer and fluid dynamics phenomena present in these devices. The virtual tests carried out are designed so as to take into account several charging and discharging cycles until equilibrium is achieved, i.e. the same amount of energy stored in the charging phase is delivered in the discharge. As a result, the dependence of the storage capacity on the PCMs temperatures, the total energy stored/released, as well as the efficiencies of the storing process have been compared for the different thermocline, PCM-only and multi-layered thermocline-PCM configurations. Based on this analysis the selection of the best option for a given case/plant is proposed.

  • Large eddy simulation of a turbulent jet diffusion flame using the Flamelet-Progress Variable model

     Ventosa, Jordi; Lehmkuhl Barba, Oriol; Perez Segarra, Carlos David; Oliva Llena, Asensio
    European Combustion Meeting
    Presentation's date: 2013-06
    Presentation of work at congresses

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    In this work an hydrogen enriched methane flame in a non-premixed configuration is studied, which corresponds to the DLR flame A. Large Eddy Simulation (LES) will be used to numerically analyse the case. Unstructured meshes are used and coupled with conservative discretisations of the differential operators. Chemical kinetics are modelled using the Flamelet/Progress-Variable model, taking into account differential diffusion effects. Computed first and second moments of the transported variables are shown to be in agreement with the experimental data.

  • Large eddy simulation model assessment of the turbulent flow through dynamic compressor valves

     Estruch Perez, Olga; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; Oliva Llena, Asensio; Perez Segarra, Carlos David
    International Conference on Compressors and Coolants
    Presentation's date: 2013-09-03
    Presentation of work at congresses

    Read the abstract Read the abstract  Share Reference managers Reference managers Open in new window

    The present paper attempts the dynamic simulation of the fluid flow through the valve reed taking into account valve movement due to piston displacement. This work widens previous studies based on numerical experiments with static geometry and constant boundary conditions. Hence, in this work attends the newly in-house implemented CFD and moving mesh coupled code TermoFluids. The CFD solver consists of a three-dimensional explicit finite volume fractional-step algorithm formulated in a second-order, conservative and collocated unstructured grid arrangement. Large eddy simulation is performed to solve the turbulent flow, using the subgrid scale WALE model. A radial basis function interpolation procedure is used to dynamically move the mesh according with the displacement of the valve. A simplified geometry of an axial hole plus a radial diffuser with a piston based inlet condition is considered. The valve dynamics is assumed to be given by a law according modal analysis of valve reed.

  • A parallel object oriented code framework for numerical simulation of reciprocating compressors - introduction of solid parts modeling

     Lopez Mas, Joan; Rigola Serrano, Joaquim; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
    International Conference on Compressors and Their Systems
    Presentation's date: 2013-09-09
    Presentation of work at congresses

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    A partitioned coupled approach is employed to modeling a reciprocating compressor in a modular way. The approach allows the implementation of an object oriented parallel code framework for simulation of multiphysics systems in general and hermetic reciprocating compressors in particular. Several works in compressor modeling have been presented before. Those works already addressed the resolution of the fluid flow by using this code framework. Now, a new model for simulation of solid components has been developed. In this way the thermal effect of the solid parts on the working fluid can be considered as well. Some numerical results are presented to show first achievements in this research line. © The author(s) and/or their employer(s), 2013.

  • Direct numerical simulation of viscoplastic-type non-Newtonian fluid flows in stenosed arteries

     Carmona Muñoz, Angel; Lehmkuhl Barba, Oriol; Perez Segarra, Carlos David; Oliva Llena, Asensio
    European Turbulence Conference
    Presentation's date: 2013-09-01
    Presentation of work at congresses

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    The aim of this work is to provide DNS solutions for turbulence flows of viscoplastic-type non-Newtonian fluids and thus contribute to gain insight into the underlying physics of the non-Newtonian turbulent flows. This knowledge may be useful, among many other things, for developing more accurate turbulence models which describe better the implicit physics of this subject. Nevertheless, from our point of view, few DNS solutions of viscoplastic-type non-Newtonian fluid flows have been provided with this objective, despite the growing presence of these kind of fluids in the field of CFD simulations.

  • Parallel large eddy simulations of wind farms with the actuator line method

     Baez Vidal, Aleix; Lehmkuhl Barba, Oriol; Martinez Valdivieso, Daniel; Perez Segarra, Carlos David
    International Conference on Parallel Computational Fluid Dynamics
    Presentation's date: 2013-05-21
    Presentation of work at congresses

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    Parallel Computation of wind farm Large Eddy Simulations (LES) requires the use of with Wind Turbine Models (WTM). CFD and WTM demand different domain decompositions as optimal CFD and WTM decompositions do not necessarily coincide. Nevertheless, data exchange between CFD and WTM must not penalize overall simulation performance. A coupling strategy for data exchange is described and has been tested. It enables the parallel simulation of wind farms with WTM. Simulations of wind turbine wakes have been achieved. Preliminary results show the parallelization works properly but that the simulations do not resolve flows with enough accuracy.

  • High performance computing of the flow past a circular cylinder at critical and supercritical Reynolds numbers

     Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Borrell, Ricard; Paniagua Sánchez, Leslye; Perez Segarra, Carlos David
    International Conference on Parallel Computational Fluid Dynamics
    Presentation's date: 2013-05-22
    Presentation of work at congresses

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    It is well known that the flow past a circular cylinder at critical Reynolds number combines flow separation, turbulence transition, reattachment of the flow and further turbulent separation of the boundary layer. In the critical regime, the transition to turbulence in the boundary layer causes the delaying of the separation point and, an important reduction of the drag force on the cylinder surface known as the Drag Crisis. In this paper advanced turbulence simulations at Reynolds numbers in the range of 1.4 × 105-8.5 × 105 will be carried out by means of large-eddy simulations. Numerical simulations using unstructured grids up to 70 million of control volumes have been performed on Marenostrum Supercomputer. One of the major outcomes is shedding some light on the shear layer instabilities mechanisms and their role on the drag crisis phenomena.

  • Study of the autoignition of a hydrogen jet in a turbulent co-flow of heated air using LES modelling

     Muela Castro, Jordi; Ventosa, Jordi; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
    European Combustion Meeting
    Presentation's date: 2013-06
    Presentation of work at congresses

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    The autoignition process of a hydrogen jet into a preheated turbulent air stream is numerically studied. A Progress-variable model with the turbulence-chemistry interaction s modelled using a Presumed Conditional Moment (PCM) closure has been used. Furthermore, the same case is studied using a Finite Rates model without closure for the reaction rate. The PV-PCM model reproduces satisfactorily the physical behaviour found in the experiments, although the model tends to underpredict the autoignition length. The results of the Finite Rates also capture accurately the autoignition phenomenology observed experimentally and the autoignition lengths are closer to those obtained in the experiment.

  • Direct numerical simulation of incompressible flows on unstructured meshes using hybrid CPU/GPU supercomputers

     Oyarzún Altamirano, Guillermo; Borrell, Ricard; Gorobets, Andrei; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
    International Conference on Parallel Computational Fluid Dynamics
    Presentation's date: 2013-05-23
    Presentation of work at congresses

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    This paper describes a hybrid MPI-CUDA parallelization strategy for the direct numerical simulation of incompressible flows using unstructured meshes. Our in-house MPI-based unstructured CFD code has been extended in order to increase its performance by means of GPU co-processors. Therefore, the main goal of this work is to take advantage of the current hybrid supercomputers to increase our computing capabilities. CUDA is used to perform the calculations on the GPU devices and MPI to handle the communications between them. The main drawback for the performance is the slowdown produced by the MPI communication episodes. Consequently, overlapping strategies, to hide MPI communication costs under GPU computations, are studied in detail with the aim to achieve scalability when executing the code on multiple nodes.

  • On the CFD&HT of the flow around a parabolic trough solar collector under real working conditions

     Amine Hachicha, Ahmed; Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
    Solar Power and Chemical Energy Systems Conference
    Presentation's date: 2013-09
    Presentation of work at congresses

    Read the abstract Read the abstract  Share Reference managers Reference managers Open in new window

    Parabolic trough solar collector is currently one of the most mature and prominent solar applications for production of electricity. These systems are usually located in open terrain where strong winds may occur and affect their stability and optical performance, as well as, the heat exchange between the solar receiver and the ambient air. In this context, a wind flow analysis around a parabolic trough solar collector under real working conditions is performed. A numerical aerodynamic and heat transfer study based on Large Eddy Simulations is carried out to characterize the wind loads and the heat transfer coefficients. Computations are performed for two Reynolds number ReW1=3.9×10^5 and ReW2=1×10^6 and various pitch angles. The effects of wind speed and pitch angle on the averaged and instantaneous flow have been assessed. The aerodynamic coefficients are calculated around the solar collectorand validated with measurements performed in wind tunnel tests. The variation of the heat transfer coefficient around the heat collector element with the Reynolds number is presented and compared to the circular cylinder in cross flow.

  • Large-eddy simulations of turbulent flow around a wall-mounted cube using an adaptive mesh refinement approach

     Antepara Zambrano, Oscar; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio; Favre, Federico
    European Turbulence Conference
    Presentation's date: 2013-09-04
    Presentation of work at congresses

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    In the present work two LES models for predicting turbulent flow and an Adaptive Mesh Refinement (AMR) technique are proposed and tested for a fully 3D geometry: turbulent flow around a wall-mounted cube at Reh=7235. The wall-adapting eddy viscosity model within a variational multiscale method (VMS-WALE) and the QR model are tested to predict the flow around the body. The numerical algorithm used to solve the governing equations preserves the symmetry and conservation properties. AMR algorithm is applied to get enough grid-resolution to solve the vortical structures near the body, adapting the mesh according to physics-based refinement criteria. High order conservative schemes are applied in the connection between coarse and fine regions. The numerical results obtained are assessed and compared to the results of the direct numerical simulations (DNS) on the basis of first and second order statistics.

  • Large eddy simulation of hydrogen autoignition in a preheated turbulent co-flow

     Muela Castro, Jordi; Ventosa, Jordi; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
    Mediterranean Combustion Symposium
    Presentation's date: 2013-09
    Presentation of work at congresses

    Read the abstract Read the abstract  Share Reference managers Reference managers Open in new window

    The autoignition process of a hydrogen jet into a preheated turbulent air stream is numerically studied. A Progress-variable (PV) model with the turbulence-chemistry interactions modelled using a Presumed Conditional Moment (PCM) closure has been used. Furthermore, the same case is studied using a Finite Rates model without closure for the reaction rate. The PV-PCM model reproduces satisfactorily the physical behaviour found in the experiments, although the model tends to underpredict the autoignition length. The results of the Finite Rates model also capture accurately the autoignition phenomenology observed experimentally and the autoignition lengths are closer to those obtained in the experiment.

  • Transient and dynamic numerical simulation of the fluid flow through valves based on large eddy simulation models

     Estruch Perez, Olga; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; Oliva Llena, Asensio; Perez Segarra, Carlos David
    International Conference on Compressors and Their Systems
    Presentation's date: 2013-09-09
    Presentation of work at congresses

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    The present paper attempts the dynamic simulation of the fluid flow through valve reed using the in-house implemented CFD and moving mesh coupled code TermoFluids. The CFD solver is based on a parallel, second-order, conservative and unstructured finite volume discretization. Large eddy simulation is performed to solve the turbulent flow, using the subgrid scale WALE model. The moving mesh technique uses RBF interpolation. As a preliminary approach, a simplified geometry of an axial hole plus a radial diffuser with a piston based inlet condition is considered. The valve dynamics is modelled by a specific law according modal analysis of valve reed. © The author(s) and/or their employer(s), 2013.

  • Large eddy simulation of a turbulent jet diffusion flame using unstructured meshes

     Ventosa, Jordi; Muela Castro, Jordi; Lehmkuhl Barba, Oriol; Perez Segarra, Carlos David; Oliva Llena, Asensio
    Mediterranean Combustion Symposium
    Presentation's date: 2013-09
    Presentation of work at congresses

    Read the abstract Read the abstract  Share Reference managers Reference managers Open in new window

    In this work an hydrogen enriched methane flame in a non-premixed configuration is studied, which corresponds to the DLR flame A. Large Eddy Simulation (LES) will be used to numerically analyse the case. Unstructured meshes are used and coupled with conservative discretisations of the differential operators. Chemical kinetics are modelled using the Flamelet/Progress-Variable model, taking into account differential diffusion effects. Computed first and second moments of the transported variables are shown to be in agreement with the experimental data.

  • Dynamic wall modelling for large-eddy simulation of wind turbine dedicated airfoils

     Calafell Sandiumenge, Joan; Lehmkuhl Barba, Oriol; Rodriguez Pérez, Ivette Maria; Oliva Llena, Asensio
    European Turbulence Conference
    Presentation's date: 2013-09
    Presentation of work at congresses

    Read the abstract Read the abstract  Share Reference managers Reference managers Open in new window

    This work aims at modelling the flow behaviour past airfoils used for wind turbine blades at high Reynolds number and large angles of attack (AoA). A previous work has been carried out on the airfoil profiles of DU-93-W-210, DU-91-W2-250 and FX-77-W-500 with a parallel unstructured symmetry preserving formulation together with wall-adapting Local-eddy viscosity model within a variational multi-scale framework (VMS-WALE) as a subgrid-scale model. However for the FX-77-W-500 profile, a mismatch between experimental results and numerical ones has been observed for the drag coefficient. To overcome this disagreement, a dynamic wall model has been implemented in order to compute accurately the wall shear stress without increasing prohibitively the computational costs.

  • Direct numerical simulation of incompressible flows on unstructured meshes using hybrid CPU/GPU supercomputers

     Oyarzún Altamirano, Guillermo; Borrell, Ricard; Gorobets, Andrey; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
    Procedia engineering
    Date of publication: 2013
    Journal article

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    This paper describes a hybrid MPI-CUDA parallelization strategy for the direct numerical simulation of incompressible flows using unstructured meshes. Our in-house MPI-based unstructured CFD code has been extended in order to increase its performance by means of GPU co-processors. Therefore, the main goal of this work is to take advantage of the current hybrid supercomputers to increase our computing capabilities. CUDA is used to perform the calculations on the GPU devices and MPI to handle the communications between them. The main drawback for the performance is the slowdown produced by the MPI communication episodes. Consequently, overlapping strategies, to hide MPI communication costs under GPU computations, are studied in detail with the aim to achieve scalability when executing the code on multiple nodes.

  • Advanced CFD&HT numerical modeling of solar tower receivers

     Colomer Rey, Guillem; Chiva Segura, Jorge; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
    Solar Power and Chemical Energy Systems Conference
    Presentation's date: 2013-09-18
    Presentation of work at congresses

    Read the abstract Read the abstract  Share Reference managers Reference managers Open in new window

    This paper presents an advanced methodology for the detailed modeling of the heat transfer and fluid dynamics phenomena in solar tower receivers. It has been carried out in the framework of a more ambitious enterprise which aims at modeling all the complex heat transfer and fluid dynamics phenomena present in central solar receivers. The global model is composed of 4 sub-models (heat conduction, two-phase flow, thermal radiation and natural convection) which are described.

  • On the large-eddy simulation modelling of wind turbine dedicated airfoils at high Reynolds numbers

     Calafell Sandiumenge, Joan; Lehmkuhl Barba, Oriol; Rodriguez Pérez, Ivette Maria; Oliva Llena, Asensio
    International Symposium on Turbulence, Heat and Mass Transfer
    Presentation's date: 2012-09-27
    Presentation of work at congresses

    View View Open in new window  Share Reference managers Reference managers Open in new window

  • Towards the high performance computing of molten salt tanks for CSP plants

     Rodriguez Pérez, Ivette Maria; Perez Segarra, Carlos David; Estruch Perez, Olga; Oliva Llena, Asensio; Lehmkuhl Barba, Oriol
    Solar Power and Chemical Energy Systems Conference
    Presentation's date: 2012-09-12
    Presentation of work at congresses

     Share Reference managers Reference managers Open in new window

  • Flow and turbulent structures around simplified car models

     Aljure Osorio, David E.; Rodriguez Pérez, Ivette Maria; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Oliva Llena, Asensio
    Conference on Modelling Fluid Flow
    Presentation's date: 2012-09-06
    Presentation of work at congresses

    View View Open in new window  Share Reference managers Reference managers Open in new window

  • Numerical solutions for the fluid flow and the heat transfer of viscoplastic-type non-Newtonian fluids

     Carmona Muñoz, Angel; Perez Segarra, Carlos David; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
    European Thermal Sciences Conference
    Presentation's date: 2012
    Presentation of work at congresses

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    The aim of this work is to provide numerical solutions for the fluid flow and the heat transfer generated in closed systems containing viscoplastic-type non-Newtonian fluids. A lid driven cavity (LDC) and a differentially heated cavity (DHC) are used as test cases. These numerical solutions can be an appropriate tool for verifying CFD codes which have been developed or adapted to deal with this kind of non-Newtonian fluids. In order to achieve this objective, an in-house CFD code has been implemented and correctly verified by the method of manufactured solutions and by some numerical solutions too. Furthermore, a high-performance CFD code (Termo Fluids S.L.) has been adapted and properly verified, by the corresponding numerical solutions, to deal with this kind of non-Newtonian fluids. The viscoplastic behaviour of certain non-Newtonian fluids will be generated from a viscous stress which has been defined by a potential-type rheological law. The pseudoplastic and dilatant behaviours will be studied. On this matter, the influence of different physical aspects on the numerical simulations will be analysed, e.g. different exponent values in the potential-type rheological law and different values of the non-dimensional numbers. Moreover, the influence of different numerical aspects on the numerical simulations will also be analysed, e.g. unstructured meshes, conservative numerical schemes and more efficient and parallel algorithms and solvers.

  • Numerical modeling of simultaneous heat and moisture transfer under complex geometry for refrigeration purposes

     Hou, Xiaofei; Rigola Serrano, Joaquim; Lehmkuhl Barba, Oriol; Oliet Casasayas, Carles; Perez Segarra, Carlos David
    European Thermal Sciences Conference
    Presentation's date: 2012
    Presentation of work at congresses

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    The aim of the paper is to gain a better insight into heat and moisture transfer in refrigerator and to do fundamental study for water evaporation and condensation in refrigeration application. The governing transport equations (continuity, momentum, energy and concentration equations) in 3D Cartesian coordinates are firstly introduced. As the mixed convection is simulated in the paper, buoyancy forces caused by both temperature and concentration gradient are considered and are also included in momentum equation. Numerical results are carried out by using Termofluids code. The pressure-velocity linkage is solved by means of an explicit finite volume fractional step procedure. In order to validate the code, a humid air flowing in a horizontal 3D rectangular duct case is carried out and compared with the published numerical and experimental results. The contour of temperature and vapor density of air at a cross section is provided and analyzed. Finally, the heat and mass transfer process during the moist air flow through complicated geometry is simulated and temperature and humidity distributions are obtained.

  • Access to the full text
    Numerical simulation of heat transfer and fluid flow in a flat plate solar collector with TIM and ventilation channel  Open access

     Kessentini, Hamdi; Lehmkuhl Barba, Oriol; Capdevila Paramio, Roser; Castro Gonzalez, Jesus; Oliva Llena, Asensio
    ISES Europe Solar Conference
    Presentation's date: 2012-09-20
    Presentation of work at congresses

    Read the abstract Read the abstract Access to the full text Access to the full text Open in new window  Share Reference managers Reference managers Open in new window

    Flat plate solar collector with plastic transparent insulation materials and ventilation channel as overheating protection system inserted between the absorber and the back insulation has been studied numerically. First, a general object-oriented unsteady model of this solar collector is developed and presented. It allows solving, in parallel way, every component separately and interacting with its neighbors to set the boundary conditions in every time step of the simulation. Every component can be simulated using its own mesh and the number of CPUs necessary (depending on the simulation level needed). Second, the numerical simulations of the fluid flow and heat transfer by natural convection in the bottom part (ventilation channel) and the upper part (air gap + TIM) of the collector are done separately. The simulation has taken into account the different operation modes of the channel (opened at high operation temperatures and closed in normal operations). A three dimensional parallel turbulent CFD model based on Large Eddy Simulation is used in the simulations. The obtained numerical results are validated with experimental and benchmark results found in the literature.

  • Numerical simulation of incompressible two phase flows by conservative level set method

     Balcazar Arciniega, Nestor Vinicio; Jofre Cruanyes, Lluís; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; Castro Gonzalez, Jesus
    Conference on Modelling Fluid Flow
    Presentation's date: 2012-09-04
    Presentation of work at congresses

    View View Open in new window  Share Reference managers Reference managers Open in new window

  • Low Mach Navier-Stokes equations on unstructured meshes

     Ventosa Molina, Jordi; Chiva Segura, Jorge; Lehmkuhl Barba, Oriol; Perez Segarra, Carlos David; Oliva Llena, Asensio
    Conference on Modelling Fluid Flow
    Presentation's date: 2012-09-04
    Presentation of work at congresses

    View View Open in new window  Share Reference managers Reference managers Open in new window

  • Combined heat and moisture transfer in buildings systems

     Damle, Rashmin; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; Oliva Llena, Asensio
    International High Performance Buildings Conference
    Presentation's date: 2012-07-18
    Presentation of work at congresses

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    Temperature and humidity are the two main parameters indicating the comfort level of the building occupants. Although the effect of temperature is taken into account in thermal simulation of buildings, the moisture transfer through the rooms and porous building walls is sometimes neglected. The level of humidity can give different sensations of thermal comfort. It is necessary to take into account both heat and moisture transport in and around buildings to predict the hygrothermal behavior of rooms and building walls so as to calculate the energy demands correctly. In this work some benchmark exercises are worked out to see the performance of the heat and moisture transfer model implemented for rooms and porous walls. Finally, numerical results are compared with the measured data for a room exposed to varying outdoor conditions.

  • Direct numerical simulation of the turbulent natural convection flow in an open cavity of aspect ratio 4

     Chiva Segura, Jorge; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Oliva Llena, Asensio
    International Symposium on Turbulence, Heat and Mass Transfer
    Presentation's date: 2012-09-24
    Presentation of work at congresses

    View View Open in new window  Share Reference managers Reference managers Open in new window

  • Large-eddy simulation of turbulent dynamic fluid-structure interaction

     Estruch Perez, Olga; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Perez Segarra, Carlos David
    International Symposium on Turbulence, Heat and Mass Transfer
    Presentation's date: 2012-09-24
    Presentation of work at congresses

    View View Open in new window  Share Reference managers Reference managers Open in new window

  • Flow and heat transfer in a wall-bounded pin matrix

     Paniagua Sánchez, Leslye; Oliet Casasayas, Carles; Lehmkuhl Barba, Oriol; Perez Segarra, Carlos David
    International Symposium on Turbulence, Heat and Mass Transfer
    Presentation's date: 2012-09-26
    Presentation of work at congresses

    View View Open in new window  Share Reference managers Reference managers Open in new window

  • Conservation properties and accuracy of unstructured mesh schemes for the Navier Stokes equations

     Jofre Cruanyes, Lluís; Lehmkuhl Barba, Oriol; Ventosa Molina, Jordi; Oliva Llena, Asensio
    International Symposium on Turbulence, Heat and Mass Transfer
    Presentation's date: 2012-09-26
    Presentation of work at congresses

    View View Open in new window  Share Reference managers Reference managers Open in new window

  • Detailed numerical model for the receiver of a solar power tower plant

     Chiva Segura, Jorge; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
    Solar Power and Chemical Energy Systems Conference
    Presentation's date: 2012-09-12
    Presentation of work at congresses

     Share Reference managers Reference managers Open in new window

  • Numerical modelling of the phase change material heat accumulator under fast transient gasification conditions in a low thrust cryogenic propulsion (LTCP) system

     Castro Gonzalez, Jesus; Galione Klot, Pedro Andres; Morales Ruíz, Juan José; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; Perez Segarra, Carlos David; Oliva Llena, Asensio
    International Conference on Space Propulsion
    Presentation's date: 2012-05-09
    Presentation of work at congresses

    View View Open in new window  Share Reference managers Reference managers Open in new window

  • Use of a Low-Mach model on a CFD&HT solver for the elements of an object oriented program to numerically simulate hermetic refrigeration compressors

     Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; Lopez Mas, Joan; Perez Segarra, Carlos David
    International Compressor Engineering Conference
    Presentation's date: 2012-07-19
    Presentation of work at congresses

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    A powerful object oriented approach for the simulation of generic thermal systems (Damle et al., 2008) is used as a framework to numerically simulate the thermal and fluid behavior of hermetic reciprocating compressors. A physical abstraction of the compressor system provides a vertex-edge graph, defining the elements and the neighborhood relations of the system to be solved. Each one of these resulting elements is modeled in order to be solved by itself by giving their respective boundary conditions. Since each element provides its own solver tool, the coupled system can be solved in an integrated form. Into previous works, an unstructured and parallel object oriented Computational Fluid Dynamics and Heat Transfer code (from now on CFD&HT) for accurate and reliable solving of turbulent industrial flow, called TermoFluids (Lehmkuhl et al., 2007), was used to provide with CFD&HT capability the system elements (López et al., 2010). In this work, a Low-Mach based CFD&HT module (Chiva et al., 2011) implemented within the TermoFluids software has been used solve the fluid domain existing inside the shell of a reciprocating compressor, which is identified as one of the compressor elements in the abstraction stage. This improvement allows us to numerically simulate the recirculation flow inside the shell of a reciprocating compressor, providing detailed information about suction area of the compressor and allowing study of new geometric configurations of such part. Furthermore, in comparison with previously tested CFD&HT modules, the Low-Mach model allows better treatment of the compressibility effects generated at the inner elements of the compressor such as chambers, tubes and undoubtedly the compression chamber.

  • A filtered kinetic energy preserving finite volumes scheme for compressible flows

     Baez Vidal, Aleix; Lehmkuhl Barba, Oriol; Perez Segarra, Carlos David; Oliva Llena, Asensio
    Conference on Modelling Fluid Flow
    Presentation's date: 2012-09-04
    Presentation of work at congresses

    View View Open in new window  Share Reference managers Reference managers Open in new window

  • Modular simulation of vapour compression systems with an object oriented tool

     Ablanque Mejia, Nicolas; Oliet Casasayas, Carles; Rigola Serrano, Joaquim; Lehmkuhl Barba, Oriol; Perez Segarra, Carlos David
    International Referigeration and Air Conditioning
    Presentation's date: 2012-07-16
    Presentation of work at congresses

    Read the abstract Read the abstract View View Open in new window  Share Reference managers Reference managers Open in new window

    The objective of this work is to simulate vapour compression refrigeration systems through a modular approach by means of an object - oriented numerical tool called NEST. For this purpose, the global system is modeled as a collection of different elements which are linked between them. Each element represents a specific part of the system (e.g. heat exchanger, compressor, expansion device, tube, cavity, wall, etc.) and can be independently solved for given boundary conditions. The global resolution procedure is carried out by solving all the elements iteratively, transferring information between them, until a converged solution is reached. The system is easily modified by adding, subtracting or substituting any of its elements. This feature gives great flexibility to the model, not only because the configuration of the system can be clearly altered, but also because the numerical model of any element can be easily replaced allowing different levels of simulation. In this work the object - oriented methodology together with the elements description and their resolution procedures are presented. The model is validated against experimental data obtained from a refrigeration cycle working with isobutane. In addition to this, an illustrative case is presented in order to show the system capabilities.