Print Email Facebook Twitter Auto-generation in wall turbulence by the interaction of weak eddies Title Auto-generation in wall turbulence by the interaction of weak eddies Author Goudar Vishwanathappa, M. (TU Delft Fluid Mechanics) Breugem, W.P. (TU Delft Multi Phase Systems) Elsinga, G.E. (TU Delft Fluid Mechanics) Date 2016 Abstract For channel flow, we explore how commonly found weak eddies can still auto-generate and produce new eddies. Before, only strong eddies (above a threshold strength) were considered to auto-generate. Such strong eddies are rarely observed in actual turbulent flows however. Here, the evolution of two weak conditional eddies with different initial strengths, initial sizes, and initial stream-wise spacing between them is studied. The numerical procedure followed is similar to Zhou et al. [“Mechanisms for generating coherent packets of hairpin vortices in channel flow,” J. Fluid Mech. 387, 353 (1999)]. The two eddies are found to merge into a single stronger eddy when the initial upstream eddy is taller than the downstream eddy, which further auto-generates when the initial stream-wise separation is small (<120 wall units). However, it is observed that non-merging cases with small initial stream-wise separation also auto-generated. In the initial condition, the two conditional eddies are placed near to each other so their velocity fields (low-speed streaks and ejection events) get superimposed and amplified as a function of stream-wise spacing. To examine this effect, a divergence free low-speed streak is superimposed on an eddy. It is found that these low-speed streak simulations do not auto-generate. On the other hand, a rapid lift-up of an eddy by ejection events plays a role in the onset of auto-generation, which also leads to a modified interpretation of auto-generation mechanism. It differed from the existing auto-generation mechanism at the later stages of auto-generation where blockage of mean flow and shear layer deformation is considered instead of vortex dynamics. Subject EddiesRotating flowsVortex interactionsTurbulent channel flowChannel flows To reference this document use: http://resolver.tudelft.nl/uuid:d959bb0b-344d-4e68-8371-6cfa3e2f6fad DOI https://doi.org/10.1063/1.4944048 Embargo date 2017-03-21 ISSN 1070-6631 Source Physics of Fluids, 28 (3) Part of collection Institutional Repository Document type journal article Rights © 2016 M. Goudar Vishwanathappa, W.P. Breugem, G.E. Elsinga Files PDF 1.4944048.pdf 2.25 MB Close viewer /islandora/object/uuid:d959bb0b-344d-4e68-8371-6cfa3e2f6fad/datastream/OBJ/view