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    Sherry, M. Lo Jacono, D. and Sheridan, J. 2010. An experimental investigation of the recirculation zone formed downstream of a forward facing step. Journal of Wind Engineering and Industrial Aerodynamics, Vol. 98, Issue. 12, p. 888.


    Abdalla, Ibrahim Elrayah Yang, Zhiyin and Cook, Malcolm 2009. Computational analysis and flow structure of a transitional separated-reattached flow over a surface mounted obstacle and a forward-facing step. International Journal of Computational Fluid Dynamics, Vol. 23, Issue. 1, p. 25.


    Hetsch, T. and Rist, U. 2009. The influence of sweep on the linear stability of a series of swept laminar separation bubbles. European Journal of Mechanics - B/Fluids, Vol. 28, Issue. 4, p. 494.


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    Mittal, Sanjay Kottaram, Jacob J. and Kumar, Bhaskar 2008. Onset of shear layer instability in flow past a cylinder. Physics of Fluids, Vol. 20, Issue. 5, p. 054102.


    Nishino, Takafumi and Roberts, Graham T. 2008. Absolute and convective instabilities of two-dimensional bluff body wakes in ground effect. European Journal of Mechanics - B/Fluids, Vol. 27, Issue. 5, p. 539.


    Abdalla, Ibrahim E. Cook, Malcolm J. and Yang, Zhiyin 2007. Numerical study of transitional separated–reattached flow over surface-mounted obstacles using large-eddy simulation. International Journal for Numerical Methods in Fluids, Vol. 54, Issue. 2, p. 175.


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  • Journal of Fluid Mechanics, Volume 532
  • June 2005, pp. 389-411

The stability of laminar symmetric separated wakes

  • IAN P. CASTRO (a1)
  • DOI: http://dx.doi.org/10.1017/S0022112005004301
  • Published online: 27 May 2005
Abstract

Time-dependent computations of the two-dimensional incompressible uniform-velocity laminar flow past a normal flat plate (of unit half-width) in a channel are presented. Attention is restricted to cases in which the well-known anti-symmetric (von Kármán-type) vortex shedding is suppressed by the imposition of a symmetry plane on the downstream plate centreline. With a further symmetry plane at the channel's upper boundary, the only two governing parameters in the problem are the channel half-width, $H$, and the Reynolds number, $Re$ (based on the body half-width and the upstream velocity, $U$). The former is restricted to the range $3\,{\leq}\, H \,{\leq}\,30$ and the interest lies in determining the nature of the initial instability which occurs in the separated wake as $Re$ is gradually increased. It is found that for sufficiently large $H$ and at a critical $Re$, a long-time-scale global (supercritical) instability is initiated, which in its saturated (limit) state takes the form of ‘lumps’ of vorticity being periodically shed from the tail end of the separated bubble. Stability calculations of corresponding mean flow profiles (typical of those found in the separated wake) are undertaken by examining the impulse response of particular profiles via appropriate solution of the Orr–Sommerfeld equation. The results of this analysis extend those available from related published work and are consistent with the behaviour found from the numerical computations. Taken together, all the results suggest that this type of global instability may be generic to many kinds of separated wakes and, indeed, may provide the fundamental explanation for the very low-frequency oscillations often noticed in fully turbulent wake bubbles.

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Journal of Fluid Mechanics
  • ISSN: 0022-1120
  • EISSN: 1469-7645
  • URL: /core/journals/journal-of-fluid-mechanics
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