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 - 3 of 3
  • 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 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.