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Experimental study on the instability of wake of axisymmetric streamlined body

Published online by Cambridge University Press:  29 March 2011

MASAHITO ASAI ,
AYUMU INASAWA ,
YASUFUMI KONISHI ,
SHINICHI HOSHINO  and
SHOHEI TAKAGI
MASAHITO ASAI*
Affiliation:
Department of Aerospace Engineering, Tokyo Metropolitan University, 6-6 Asahigaoka, Hino, Tokyo 191-0065, Japan
AYUMU INASAWA
Affiliation:
Department of Aerospace Engineering, Tokyo Metropolitan University, 6-6 Asahigaoka, Hino, Tokyo 191-0065, Japan
YASUFUMI KONISHI
Affiliation:
Department of Aerospace Engineering, Tokyo Metropolitan University, 6-6 Asahigaoka, Hino, Tokyo 191-0065, Japan
SHINICHI HOSHINO
Affiliation:
Department of Aerospace Engineering, Tokyo Metropolitan University, 6-6 Asahigaoka, Hino, Tokyo 191-0065, Japan
SHOHEI TAKAGI
Affiliation:
Aerospace Plane Research Center, Muroran Institute of Technology, 27-1 Mizumoto-cho, Muroran 050-8585, Japan
*
†Email address for correspondence: masai@sd.tmu.ac.jp
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Abstract

The instability of wake of an axisymmetric body with the NACA aerofoil section was experimentally studied under low background turbulence. The body was suspended using a magnetic suspension and balance system to avoid undesirable influences of mechanical supports on the disturbance development. The Reynolds number based on the chord length of the aerofoil section ranged from 5.3 × 104 to 2.1 × 105. For the body with a NACA0015 aerofoil section where there is no boundary-layer separation on the body surface, the wake was convectively unstable, even at the highest Reynolds number examined. Although the wake maintained axisymmetry of mean flow, the instability waves often took a planar-symmetric form, indicating that the occurrence of disturbance can be influenced by minute variations in the position and orientation of the suspended body. For bodies with thicker NACA0018 and NACA0024 aerofoil sections where the flow involved a region of absolute instability immediately downstream of the trailing edge, the global mode could grow rapidly and attain saturation amplitude within a very short distance from the trailing edge despite that the region of absolute instability was limited only to small streamwise distance, about one tenth of the instability wavelength. The predominant frequency of vortex shedding was found to be very close to the absolute frequency near the trailing edge, especially at the upstream boundary of the region of absolute instability. This is consistent with the theoretical model for the development of a nonlinear global mode. It was also found that the mean flow axisymmetry was broken around the critical Reynolds number for global instability, which led to the appearance and growth of a planar-symmetric global mode.

JFM classification

Instability: Absolute/convective instability Wakes/Jets: Wakes
Type
Papers
Information
Journal of Fluid Mechanics , Volume 675 , 25 May 2011 , pp. 574 - 595
Copyright
Copyright © Cambridge University Press 2011

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