Pinelli, Alfredo

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Universidad Complutense de Madrid
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Ciencias Matemáticas
Matemática Aplicada
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Now showing 1 - 8 of 8
  • Publication
    LES and RANS simulations of the MUST experiment. Study of incident wind direction effects on the flow and plume dispersion
    (2007) Santiago, J. L.; Dejoan, A.; Martilli, A.; Martín , F.; Pinelli, Alfredo
    In this study, we propose to assess and compare the performance of LES and RANS methodologies for the simulation of pollutant dispersion in an urban environment by making use of field and wind tunnel measurements of the MUST experiment configuration. First, the proposed analysis addresses the relevance of taking into account the small geometrical irregularities of the obstacle array in the computations. For this, local and spatial averaged time mean flow properties are compared for two geometries, one with a perfect alignment of the containers and another one including the irregularities present in the experiment. In both geometries the incident flow is orthogonal to the front array of obstacles. The second part of this study presents simulations with different approaching wind directions to analyse the effect of small changes in the incident wind direction on the flow and on the plume dispersion. In this second part, the mean concentration field is compared with the experimental data and an analysis that relates the channelling effects with the plume deflection is provided.
  • Publication
    Turbulent puffs in a horizontal square duct under stable temperature stratification
    (Begell House, 2012) Otsuki, T.; Kawahara, Genta; Uhlmann, Markus; Pinelli, Alfredo
    Direct numerical simulations of streamwise-localized turbulent flow (turbulent puff) in a horizontal square duct heated from above are performed at Richardson numbers 0 ≤ Ri ≤ 0.58 to characterize differences between isothermal and non-isothermal puffs. It is found that the structure of the non-isothermal puff exhibits significantly different properties from that of the isothermal puff. In particular, differences are observed in wall shear stresses. In the upstream part of the non-isothermal puff, higher shear appears on the horizontal walls than the vertical ones. In the downstream part, meanwhile, higher shear appears on the vertical walls than the horizontal ones. The higher shear on the horizontal walls in the upstream part is interpreted in terms of coherent streamwise vortices induced by buoyancy in the corner regions. The higher shear on the vertical walls in the downstream part is considered to be a consequence of higher wall-normal (horizontal) turbulence intensity on the vertical walls under the weaker constraint of the stable stratification.
  • Publication
    A spectral multidomain method for the numerical simulation of turbulent flows
    (Elsevier, 1997) Pinelli, Alfredo; Vacca, A.; Quarteroni, A.
    The primitive variable formulation of the unsteady incompressible Navier-Stokes equations in three space dimensions is discretized with a combined Fourier-Legendre spectral method. A semi-implicit pressure correction scheme is applied to decouple the velocity from the pressure. The arising elliptic scaler problems are first diagonalized in the periodic Fourier direction and then solved by a multidomain Legendre collocation method in the two remaining space coordinates. In particular, both an iterative and a direct version of the so-called projection decomposition method (PDM) are introduced to separate the equations for the internal nodes from the ones governing the interface unknowns. The PDM method, first introduced by V. Agoshkov and E. Ovtchinnikov and later applied to spectral methods by P. Gervasio, E. Ovtchinnikov, and A. Quarteroni is a domain decomposition technique for elliptic boundary value problems, which is based on a Galerkin approximation of the Steklov-Poincare equation for the unknown variables associated to the grid points lying on the interface between subdomains. After having shown the exponential convergence of the proposed discretization technique, some issues on the efficient implementation of the method are given. Finally, as an illustration of the potentialities of the algorithm for the numerical simulation of turbulent flows, the results of a direct numerical simulation (DNS) of a fully turbulent plane channel flow are presented.
  • Publication
    Comparison between LES and RANS computations for the study of contaminant dispersion in the MUST field experiment
    (AMS, 2007) Dejoan, A.; Santiago, J. L.; Pinelli, Alfredo; Martilli, A.
  • Publication
    DNS of non-isothermal turbulent flows carrying low Stokes number particles
    (Elsevier, 2003) Pinelli, Alfredo; García Ybarra, P. L.
  • Publication
    Chebyshev pseudospectral solution of advection-diffusion equations with mapped finite difference preconditioning
    (Elsevier, 1994) Pinelli, Alfredo; Benocci, C.; Deville, M.
    A new Chebyshev pseudo-spectral algorithm with finite difference preconditioning is proposed for the solution of advection-diffusion equations, A mapping technique is introduced which allows good convergence for any Peclet number both for one-dimensional and two-dimensional problems. Numerical results show that first-order Lagrange polynomials are the optimal mapping procedure for the one-dimensional problem and second-order Lagrange polynomials, for the two-dimensional one.
  • Publication
    A fast Lagrangian tracking method capturing finite-size effects in particulate flows
    (American Physical Society, 2011) Wu, M.; Favier, J.; Pinelli, Alfredo
    We 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.
  • Publication
    Immersed-boundary methods for general finite-difference and finite-volume Navier-Stokes solvers
    (Elsevier, 2010) Pinelli, Alfredo; Naqavi, I.Z.; Piomelli, U.; Favier, J.
    We present an immersed-boundary algorithm for incompressible flows with complex boundaries, suitable for Cartesian or curvilinear grid system. The key stages of any immersed-boundary technique are the interpolation of a velocity field given on a mesh onto a general boundary (a line in 2D, a surface in 3D), and the spreading of a force field from the immersed boundary to the neighboring mesh points, to enforce the desired boundary conditions on the immersed-boundary points. We propose a technique that uses the Reproducing Kernel Particle Method [W.K. Liu, S. Jun, Y.F. Zhang, Reproducing kernel particle methods, Int. J. Numer. Methods Fluids 20(8) (1995) 1081-1106] for the interpolation and spreading. Unlike other methods presented in the literature, the one proposed here has the property that the integrals of the force field and of its moment on the grid are conserved, independent of the grid topology (uniform or non-uniform, Cartesian or curvilinear). The technique is easy to implement, and is able to maintain the order of the original underlying spatial discretization. Applications to two- and three-dimensional flows in Cartesian and non-Cartesian grid system, with uniform and non-uniform meshes are presented.