Stability and dynamics of the laminar wake past a slender blunt-based axisymmetric body Articles uri icon

publication date

  • June 2011

start page

  • 110

end page

  • 144

volume

  • 676

international standard serial number (ISSN)

  • 0022-1120

electronic international standard serial number (EISSN)

  • 1469-7645

abstract

  • We investigate the stability properties and flow regimes of laminar wakes behind slender cylindrical bodies, of diameter D and length L, with a blunt trailing edge at zero angle of attack, combining experiments, direct numerical simulations and local/global linear stability analyses. It has been found that the flow field is steady and axisymmetric for Reynolds numbers below a critical value, Re-cs (L/D), which depends on the length-to-diameter ratio of the body, L/D. However, in the range of Reynolds numbers Re-cs (L/D) < Re < Re-co (L/D), although the flow is still steady, it is no longer axisymmetric but exhibits planar symmetry. Finally, for Re > Re-co, the flow becomes unsteady due to a second oscillatory bifurcation which preserves the reflectional symmetry. In addition, as the Reynolds number increases, we report a new flow regime, characterized by the presence of a secondary, low frequency oscillation while keeping the reflectional symmetry. The results reported indicate that a global linear stability analysis is adequate to predict the first bifurcation, thereby providing values of Re-cs nearly identical to those given by the corresponding numerical simulations. On the other hand, experiments and direct numerical simulations give similar values of Re-co for the second, oscillatory bifurcation, which are however overestimated by the linear stability analysis due to the use of an axisymmetric base flow. It is also shown that both bifurcations can be stabilized by injecting a certain amount of fluid through the base of the body, quantified here as the bleed-to-free-stream velocity ratio, C-b = W-b/W-infinity.

keywords

  • flow control ; instability control ; wakes