DSpace Community:
http://hdl.handle.net/2117/3190
2015-04-01T18:14:14ZSpectrally-consistent regularization of turbulent Rayleigh-Bénard convection
http://hdl.handle.net/2117/26901
Title: Spectrally-consistent regularization of turbulent Rayleigh-Bénard convection
Authors: Dabbagh, Firas; Trias Miquel, Francesc Xavier; Gorobets, Andrei; Oliva Llena, Asensio
Abstract: Direct numerical simulation (DNS) of turbulent Rayleigh-Bénard convection in an air filled (Pr = 0,7) rectangular cell of squared cross-section with periodic boundary conditions in the span-wise direction, has been carried out at Ra = 10^8. A fourth-order energy-conserving discretizations have been used that ensure non-physical dissipative effects introduced usually in other numerical schemes. The two sensitive fine-scales kinetic and thermal dissipation rates have been studied statistically to reveal high correlation within the thermal boundary layers and equilibrium zones of the two dissipations at strong thermal and kinetic interactions. It has been found that the foregoing zones could mark the plumes since these last reflect significant correlation regions of the kinetic and thermal fields. Afterwards, a novel class of symmetry-preserving regularization models that restrain the convective production of small scales of motion in unconditionally stable manner, have been applied on the studied problem. The obtained results are compared directly with the DNS ones to show a reasonable correspondence with and without model at this kind of moderate turbulence.2015-03-20T13:50:56ZUnstructured 3D numerical modeling of the melting of a PCM contained in a spherical capsule
http://hdl.handle.net/2117/26897
Title: Unstructured 3D numerical modeling of the melting of a PCM contained in a spherical capsule
Authors: Galione Klot, Pedro Andrés; Lehmkuhl Barba, Oriol; Rigola Serrano, Joaquim; Pérez Segarra, Carlos David; Oliva Llena, Asensio2015-03-20T13:34:04ZDirect numerical simulation of the flow over a spherical bubble in a turbulent pipe flow
http://hdl.handle.net/2117/26896
Title: Direct numerical simulation of the flow over a spherical bubble in a turbulent pipe flow
Authors: Jofre Cruanyes, Lluís; Balcázar Arciniega, Néstor; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Castro González, Jesús
Abstract: This work aims at investigating, by means of a direct numerical simulation, the flow over a clean spherical bubble fixed on the axis of a turbulent pipe flow. The simulation is performed by means of a parallel unstructured symmetry-preserving formulation on a mesh of 5.4M cells. The main features of the turbulent flow are described by analyzing the time-averaged data collected over a significant period of time. The numerical results conclude that the bubble generates a wake, similarly to the case of a solid sphere, however, it differs in the fact that the fluid slips through the surface of the bubble instead of stopping, thus, no boundary layer is created. Moreover, due to viscosity, a transfer of momentum from the fluid surrounding the bubble to the fluid inside of it is produced. This transfer of momentum generates a turbulent toroidal vortex inside the bubble. In consequence, two short recirculation zones are found at the extremes of the bubble’s diameter, while in between, the axial velocity inverts its sign.2015-03-20T13:21:20ZNumerical modeling of simultaneous heat and moisture transfer under complex geometry for refrigeration purposes
http://hdl.handle.net/2117/26805
Title: Numerical modeling of simultaneous heat and moisture transfer under complex geometry for refrigeration purposes
Authors: Hou, Xiaofei; Rigola Serrano, Joaquim; Lehmkuhl Barba, Oriol; Oliet Casasayas, Carles; Pérez Segarra, Carlos David
Abstract: 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.2015-03-18T13:40:45ZOn the IBM approximation for the wheel aerodynamic simulation
http://hdl.handle.net/2117/26777
Title: On the IBM approximation for the wheel aerodynamic simulation
Authors: Aljure Osorio, David E.; Lehmkuhl Barba, Oriol; Martínez Valdivieso, Daniel; Favre Samarra, Federico; Oliva Llena, Asensio
Abstract: Challenging large eddy simulations (CLES) are performed to the flow around simplified wheels in wheelhouses. Wheel geometry is modelled using immersed boundary methods.
Results are compared to previous numerical simulations. Instantaneous flows results and turbulent structures are analysed to asses the viability of this boundary treatment on the resolution of a rotating wheel.2015-03-17T18:27:29ZLarge eddy simulation of a turbulent jet diffusion flame using the Flamelet-Progress Variable model
http://hdl.handle.net/2117/22039
Title: Large eddy simulation of a turbulent jet diffusion flame using the Flamelet-Progress Variable model
Authors: Ventosa, Jordi; Lehmkuhl Barba, Oriol; Pérez Segarra, Carlos David; Oliva Llena, Asensio
Abstract: 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.2014-03-13T15:40:47ZStudy of the autoignition of a hydrogen jet in a turbulent co-flow of heated air using LES modelling
http://hdl.handle.net/2117/22038
Title: Study of the autoignition of a hydrogen jet in a turbulent co-flow of heated air using LES modelling
Authors: Muela Castro, Jordi; Ventosa, Jordi; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio
Abstract: 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.2014-03-13T15:33:05ZLarge-eddy simulations of turbulent flow around a wall-mounted cube using an adaptive mesh refinement approach
http://hdl.handle.net/2117/22037
Title: Large-eddy simulations of turbulent flow around a wall-mounted cube using an adaptive mesh refinement approach
Authors: Antepara Zambrano, Óscar; Lehmkuhl Barba, Oriol; Oliva Llena, Asensio; Favre, Federico
Abstract: 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.2014-03-13T15:28:58ZBlending regularization and large-eddy simulation. From homogeneous isotropic turbulence to wind farm boundary layers
http://hdl.handle.net/2117/22034
Title: Blending regularization and large-eddy simulation. From homogeneous isotropic turbulence to wind farm boundary layers
Authors: Folch Flórez, David; Trias Miquel, Francesc Xavier; Gorobets, Andrei; Oliva Llena, Asensio
Abstract: The incompressible Navier-Stokes equations form an excellent mathematical model for turbulent flows. However, direct simulations at high Reynolds numbers are not feasible because the convective term produces far too many relevant scales of motion.
Therefore, in the foreseeable future numerical simulations of turbulent flows will have to resort to models of the small scales. Large-eddy simulation (LES) and regularization models are examples thereof. In the present work, we propose to combine both approaches.
Restoring the Galilean invariance of the regularization method results into an additional hyperviscosity term. This approach provides a natural blending between regularization and LES. The performance of these recent improvements will be assessed through application to homogeneous isotropic turbulence, a turbulent channel flow and a wind-farm turbulent boundary layer.2014-03-13T15:24:24ZDirect numerical simulation of viscoplastic-type non-Newtonian fluid flows in stenosed arteries
http://hdl.handle.net/2117/21943
Title: Direct numerical simulation of viscoplastic-type non-Newtonian fluid flows in stenosed arteries
Authors: Carmona Muñoz, Ángel; Lehmkuhl Barba, Oriol; Pérez Segarra, Carlos David; Oliva Llena, Asensio
Abstract: 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.2014-03-07T16:20:34ZFrom extruded-2D to fully-3D geometries for DNS: a multigrid-based extension of the Poisson solver
http://hdl.handle.net/2117/21618
Title: From extruded-2D to fully-3D geometries for DNS: a multigrid-based extension of the Poisson solver
Authors: Gorobets, Andrei; Trias Miquel, Francesc Xavier; Soria Guerrero, Manel; Pérez Segarra, Carlos David; Oliva Llena, Asensio
Abstract: Direct numerical simulation (DNS) of incompressible flows is an essential tool for improving the understanding of the physics of turbulence and for the development of better turbulence models. The Poisson equation, the main bottleneck from a parallel point of view, usually also limits its applicability for complex geometries. In this context, efficient and scalable Poisson solvers on fully-3D geometries are of high interest.In our previous work, a scalable algorithm for Poisson equation was proposed. It performed well on both small clusters with poor network performance and supercomputers using efficiently up to a thousand of CPUs. This algorithm named Krylov-Schur-Fourier Decomposition (KSFD) can be used for problems in parallelepipedic 3D domains with structured meshes and obstacles can be placed inside the flow. However, since a FFT decomposition is applied in one direction, mesh is restricted to be uniform and obstacles to be 2D shapes extruded along this direction.The present work is devoted to extend the previous KSFD algorithm to eliminate these limitations. The extension is based on a two-level Multigrid (MG) method that uses KSFD as a solver for second level. The algorithm is applied for a DNS of a turbulent flow in a channel with wall-mounted cube. Illustrative results at Re τ = 590 (based on the cube height and the bulk velocity Re h = 7235) are shown.2014-02-17T15:33:45ZDNS of turbulent natural convection flows on the MareNostrum supercomputer
http://hdl.handle.net/2117/21617
Title: DNS of turbulent natural convection flows on the MareNostrum supercomputer
Authors: Trias Miquel, Francesc Xavier; Gorobets, Andrei; Soria Guerrero, Manel; Oliva Llena, Asensio
Abstract: A code for the direct numerical simulation (DNS) of incompressible turbulent flows that provides a fairly good scalability for a wide range of computer architectures has been developed. The spatial discretization of the incompressible Navier-Stokes equations is carried out using a fourth-order symmetry-preserving discretization. Since the code is fully explicit, from a parallel point of view, the main bottleneck is the Poisson equation. In the previous version of the code, that was conceived for low cost PC clusters with poor network performance, a Direct Schur-Fourier Decomposition (DSFD) algorithm was used to solve the Poisson equation. Such method, that was very efficient for PC clusters, can not be efficiently used with an arbitrarily large number of processors, mainly due to the RAM requirements (that grows with the number of processors). To do so, a new version of the solver, named Krylov-Schur-Fourier Decomposition (KSFD), is presented here. Basically, it is based on the Direct Schur Decomposition (DSD) algorithm that is used as a preconditioner for a Krylov method (CG) after Fourier decomposition. Benchmark results illustrating the robustness and scalability of the method on the MareNostrum supercomputer are presented and discussed. Finally, illustrative DNS simulations of wall-bounded turbulent flows are also presented.2014-02-17T15:22:24ZLow-frequency unsteadiness in the vortex formation region of a circular cylinder
http://hdl.handle.net/2117/21548
Title: Low-frequency unsteadiness in the vortex formation region of a circular cylinder
Authors: Lehmkuhl Barba, Oriol; Rodríguez Pérez, Ivette María; Borrell Pol, Ricard; Oliva Llena, Asensio
Abstract: 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 = U ref D/ν) 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 f m = 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.
Description: Electronic version of an article published as "Physics of fluids", vol. 25, no 8, 2013. DOI: http://dx.doi.org/10.1063/1.4818641.2014-02-12T15:33:46ZFlow past a NACA0012 airfoil: from laminar separation bubbles to fully stalled regime
http://hdl.handle.net/2117/21439
Title: Flow past a NACA0012 airfoil: from laminar separation bubbles to fully stalled regime
Authors: Rodríguez Pérez, Ivette María; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Oliva Llena, Asensio2014-02-03T15:40:09ZDirect numerical simulation of a NACA0012 in full stall
http://hdl.handle.net/2117/21438
Title: Direct numerical simulation of a NACA0012 in full stall
Authors: Rodríguez Pérez, Ivette María; Lehmkuhl Barba, Oriol; Borrell Pol, Ricard; Oliva Llena, Asensio
Abstract: 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.2014-02-03T15:29:47Z