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Wakes behind a prolate spheroid in crossflow

  • George K. El Khoury (a1), Helge I. Andersson (a2) and Bjørnar Pettersen (a1)

Abstract

Viscous laminar flow past a prolate spheroid has been investigated numerically at seven different Reynolds numbers; and . In contrast to all earlier investigations, the major axis of the spheroid was oriented perpendicular to the free stream flow. As expected, the flow field in the wake showed a strong resemblance of that observed behind a finite-length circular cylinder, yet had features observed in the axisymmetric wake behind a sphere. The following different flow regimes were observed in the present computational study: (i) steady laminar flow with massive flow separation and symmetry about the equatorial and the meridional planes at ; (ii) steady laminar flow with massive flow separation and symmetry about the equatorial and the meridional plane at , but the flow in the equatorial plane did no longer resemble the steady wake behind a circular cylinder; (iii) unsteady laminar flow with Strouhal number and symmetry about the equatorial plane at ; (iv) unsteady laminar flow with two distinct frequencies and without any planar symmetries at ; (v) transitional flow with a dominant shedding frequency and without any spatial symmetries at . For all but the two lowest hairpin vortices were alternately shed from the two sides of the spheroid and resulted in a ladder-like pattern of oppositely oriented vortex structures, in contrast with the single-sided shedding in the wake of a sphere. The contour of the very-near-wake mimicked the shape of the prolate spheroid. However, downstream the major axis of the wake became aligned with the minor axis of the spheroid. This implies that an axis switching occurred some downstream, i.e. the cross-section of the wake evolved such that the major and minor axes interchanged at a certain downstream location. This peculiar phenomenon has frequently been reported to arise for elliptical and rectangular jets, whereas observations of axis switching for asymmetric wakes are scarce.

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Corresponding author

Email address for correspondence: george.e.khoury@ntnu.no

References

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