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 - 4 of 4
  • Publication
    The autonomous cycle of near-wall turbulence
    (Cambridge University Press, 1999) Jiménez, Javier; Pinelli, Alfredo
    Numerical experiments on modified turbulent channels at moderate Reynolds numbers are used to differentiate between several possible regeneration cycles for the turbulent fluctuations in wall-bounded flows. It is shown that a cycle exists which is local to the near-wall region and does not depend on the outer flow. It involves the formation of velocity streaks from the advection of the mean profile by streamwise vortices, and the generation of the vortices from the instability of the streaks. Interrupting any of those processes leads to laminarization. The presence of the wall seems to be only necessary to maintain the mean shear. The generation of secondary vorticity at the wall is shown to be of little importance in turbulence generation under natural circumstances. Inhibiting its production increases turbulence intensity and drag.
  • Publication
    The role of coherent structure interactions in the regeneration of wall turbulence
    (Springer, 1998) Jiménez, Javier; Pinelli, Alfredo
    The near-wall region is characterized by the presence of organized structures [1], but the way in which they interact to maintain the local dynamics and to extract energy from the mean flow is still controversial. The two dominant structures are the streamwise velocity streaks and the quasi-streamwise vortices. The former consist of long (x + ~ 1000) wavy arrays of alternating streamwise jets with an average spanwise wavelength of z + ~ 100. The latter are vortical structures almost aligned with the mean flow but slightly tilted away from the wall. While it is generally accepted that the vortices induce streaks by transferring mean streamwise momentum towards and away from the wall [2], there is less consensus on the generation mechanism of the streamwise vortices. Two conceptual models, widely discussed in the literature, are illustrated in Fig. 1: A) the streamwise vortices are a consequence of the breakdown of the streaks, probably due to inflectional instabilities of the local velocity profiles; B) the streamwise vortices are formed directly, or at least triggered, by the amplification of outer flow perturbations. Hypothesis A assumes that an autonomous wall cycle exists, while B predicts that wall turbulence depends on the existence of an outer flow.
  • Publication
    The instability of streaks in near-wall turbulence
    (Center for Turbulence Research, 1998) Kawahara, Genta; Jiménez, Javier; Uhlmann, Markus; Pinelli, Alfredo
  • Publication
    Wall turbulence: How it works and how to damp it
    (American Institute of Aeronautics and Astronautics, 1997) Jiménez, Javier; Pinelli, Alfredo