Person: Pinelli, Alfredo
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First Name
Alfredo
Last Name
Pinelli
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Matemáticas
Department
Area
Matemática Aplicada
Identifiers
56 results
Search Results
Now showing 1 - 10 of 56
Item Large Eddy simulation of turbulence on an alliant FX computer(Supercomputer, 1990) Benocci, C.; Pinelli, Alfredo; Abba, A.Item The autonomous near-wall turbulent region(American Physical Society, Division of Fluid Dynamics Meeting, November 22-24, 1998 Philadelphia, PA, abstract #AH.04, 1998) Jiménez, J.; Pinelli, AlfredoThe near-wall region is the only place in zero-pressure-gradient boundary layer where the production of turbulent energy exceeds dissipation. The excess energy helps maintain turbulence in the core region, where the opposite is true. It is shown that it is possible to maintain turbulence in the region below y^+≈ 60 without any input from the outer flow. In the numerical experiment all the fluctuations in a plane channel are artificially damped by increasing viscosity with height, and the outer flow is laminar above that level. The near-wall region nevertheless survives indefinitely, suggesting that wall turbulence can be studied in terms of modular units, with the near-wall and the logarithmic and outer layers as interacting but distinct phenomena. The cycle responsible for maintaining near-wall turbulence is shown to involve low-velocity streaks and streamwise vortices, but essentially no hairpins. The intensity of the near-wall longitudinal velocity fluctuations agrees well with those in fully developed flows, but the wall-normal fluctuations are weaker, in agreement with the Reynolds number behaviour found experimentally for those quantities. The reason is explored using higher Reynolds number simulations.Item Toward direct numerical simulation of reacting fluidized beds(Proceedings of the 3rd European Combustion Meeting, 2003) Uhlmann, Markus; Pinelli, Alfredo; GarcÃa Ybarra, P. L.Nowadays, the most used techniques to design dense gas-solid flow reactors rely upon numerical predictions obtained from hydrodynamic models, usually derived through some averaging processes of the complete conservation equations. The averaging process leads to unknown correlation terms that need further modeling for the final closure of the equations. Many of these terms represent complex interactions between phases and are usually modeled through semi-empirical relations. Direct Numerical Simulation (DNS) of idealized situations can help in grasping the basic mechanisms governing these systems, therefore fostering the development of improved models.Item Two-dimensional thermal convection flow with variable viscosity and embedded boundaries(2003) Uhlmann, Markus; Pinelli, AlfredoA two-dimensional model capable of simulating thermal convection flow in complex geometries has been implemented in a finite-difference setting and using a fictitious domain method of type “direct explicit forcing". The Boussinesq approximation is supposed to hold; the coupling between velocity and temperature fields is explicit; spatially varying viscosity is accounted for. The computation of a model for the thermally-induced flow in a three-chamber fuel tank reveals that the present method does not allow for sufficiently large time steps when the viscosity varies strongly.Item A fast Lagrangian tracking method capturing finite-size effects in particulate flows(Bulletin of the American Physical Society, 2011) Wu, M.; Favier, J.; Pinelli, AlfredoWe present a new method to capture the finite-size effects induced by particles transported by a fluid flow, with a low computational cost compared to available fully-resolved methods, thus allowing to tackle configurations with high volume fractions of particles. The basic idea consists in tracking a source/sink of momentum occurring within a compact support of the mesh, centered on the particle and taking the form of a mollified Dirac kernel, or blob. In the spirit of the immersed boundary method, the shape and the intensity of the kernel are found by imposing appropriate reproducing conditions on the blob (to model accurately a Dirac pulse) and spreading on the mesh cells a volume force determined by the desired boundary condition. The particles occupy a finite-size volume of fluid, therefore introducing a two-way coupled behavior, for the computational cost of only one Lagrangian point. To build the blobs, we will either spread a zero-velocity condition at the blob center, or spread a zero-velocity condition averaged on the fluid parcel enclosed within the support. Both methods are discussed and validated by comparing with free falling fully-resolved particles, in 2D and 3D.Item Interaction of multiple flapping filaments for cylinder wake modification using the Lattice Boltzmann Method(ICCFD7 : International Conference On Computational Fluid Dynamics, July 9-13, 2012, Mauna Lani Bay Hotel, Island of Hawaii, 2012) Revell, A.; Favier, J.; Pinelli, AlfredoThis paper introduces the recent work undertaken on the development of a code based on the combination of the Lattice Boltzmann Method (LBM) with a recent version of the Immersed Boundary Method (IBM). The code is first validated against existing results, before being applied to investigate the different modes of flapping behaviour for single and multiple filaments at various separation distances. The work proceeds to investigate the cylinder wake modification for moderate Reynolds number when groups of said filaments are attached to the ley-side of a circular cylinder.Item The instability of streaks in near-wall turbulence(Center for Turbulence Research, Annual Research Briefs, 1998) Kawahara, Genta; Jiménez, Javier; Uhlmann, Markus; Pinelli, AlfredoItem Control of the separated flow around an airfoil using a wavy leading edge inspired by humpback whale flippers(Comptes rendus. Mécanique, 2012) Favier, J.; Pinelli, Alfredo; Piomelli, U.The influence of spanwise geometrical undulations of the leading edge of an infinite wing is investigated numerically at low Reynolds number, in the context of passive separation control and focusing on the physical mechanisms involved. Inspired by the tubercles of the humpback whale flippers, the wavy leading edge is modeled using a spanwise sinusoidal function whose amplitude and wavelength constitute the parameters of control. A direct numerical simulation is performed on a NACA0020 wing profile in a deep stall configuration (α=20°), with and without the presence of the leading edge waviness. The complex solid boundaries obtained by varying the sinusoidal shape of the leading edge are modeled using an immersed boundary method (IBM) recently developed by the authors [Pinelli et al., J. Comput. Phys. 229 (2010) 9073–9091]. A particular set of wave parameters is found to change drastically the topology of the separated zone, which becomes dominated by streamwise vortices generated from the sides of the leading edge bumps. A physical analysis is carried out to explain the mechanism leading to the generation of these coherent vortical structures. The role they play in the control of boundary layer separation is also investigated, in the context of the modifications of the hydrodynamic performances which have been put forward in the literature in the last decade.Item Large eddy simulation of a fully turbulent plane channel flow(1989) Pinelli, Alfredo; Benocci, C.The development of a code for the large eddy simulation of wall bounded turbulent shear layers is described. The numerical approach selected is a finite difference discretization of the filtered Navier-Stokes equations, where the unresolved part of the turbulence is introduced through the Smagorinsky model of subgrid viscosity. A systematic study of the influence of mesh resolution, wall boundary condition and formulation of the advection term was performed for the case of a fully turbulent plane channel flow.Item Turbulent channel flow concentration profile and wall deposition of a large Schmidt number passive scalar(Comptes rendus. Mécanique, 2006) GarcÃa Ybarra, P. L.; Pinelli, AlfredoThe transport of a passive scalar within a turbulent plane channel flow has been theoretically analyzed by assuming that the Schmidt number Sc, associated to the molecular diffusivity of the passive scalar, is a large parameter. Throughout most of the channel cross-section the mean passive scalar density is constant, but adjacent to the walls a thin boundary layer develops embedded in the viscous sublayer, with a relative thickness of order Sc(-1/3). In this narrow region a passive scalar profile arises due to the non-vanishing flux normal to the wall. This profile is parameter independent (universal) and leads to a constant flux of passive scalar that results from the addition of both the molecular diffusion flux and the turbulent transport one. The Sc-asymptotic matching of this profile with the constant core value provides an analytical expression for the wall-normal flux that depends on the fluid dynamics of the carrier flow. By using a DNS code to solve the external turbulent flow, the analytical expression has been quantified and compared with empifical expressions based on experimental data, showing excellent agreement.