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Low-frequency unsteadiness of vortex wakes over slender bodies at high angle of attack

Authors
Journal
Chinese Journal of Aeronautics
1000-9361
Publisher
Elsevier
Volume
27
Issue
4
Identifiers
DOI: 10.1016/j.cja.2014.06.011
Keywords
  • Aerodynamics
  • Experiments
  • Fluid Dynamics
  • Unsteady Flow
  • Vortex Flow

Abstract

Abstract A type of flow unsteadiness with low frequencies and large amplitude was investigated experimentally for vortex wakes around an ogive-tangent cylinder. The experiments were carried out at angles of attack of 60–80° and subcritical Reynolds numbers of 0.6–1.8×105. The reduced frequencies of the unsteadiness are between 0.038 and 0.072, much less than the frequency of Karman vortex shedding. The unsteady flow induces large fluctuations of sectional side forces. The results of pressure measurements and particle image velocimetry indicate that the flow unsteadiness comes from periodic oscillation of the vortex wakes over the slender body. The time-averaged vortex patterns over the slender body are asymmetric, whose orientation is dependent on azimuthal locations of tip perturbations. Therefore, the vortex oscillation is a type of unsteady oscillation around a time-averaged asymmetric vortex structure.

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