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The effect of Reynolds number on the elliptical cylinder wake

  • Shi, Xiaoyu (Institute of Turbulence-Noise-Vibration Interaction and Control, Harbin Institute of Technology (Shenzhen)) ;
  • Alam, Md. Mahbub (Institute of Turbulence-Noise-Vibration Interaction and Control, Harbin Institute of Technology (Shenzhen)) ;
  • Bai, Honglei (School of Aeronautics and Astronautics, Sun Yat-sen University (Shenzhen)) ;
  • Wang, Hanfeng (School of Civil Engineering, Central South University)
  • Received : 2019.11.14
  • Accepted : 2020.01.26
  • Published : 2020.05.25
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Abstract

This work numerically investigates the effects of Reynolds number ReD (= 100 - 150), cross-sectional aspect ratio AR = ( 0.25 -1.0), and attack angle α (= 0° - 90°) on the forces, Strouhal number, and wake of an elliptical cylinder, where ReD is based on the freestream velocity and cylinder cross-section height normal to the freestream flow, AR is the ratio of the minor axis to the major axis of the elliptical cylinder, and α is the angle between the cylinder major axis and the incoming flow. At ReD = 100, two distinct wake structures are identified, namely 'Steady wake' (pattern I) and 'Karman wake followed by a steady wake (pattern II)' when AR and α are varied in the ranges specified. When ReD is increased to 150, an additional wake pattern, 'Karman wake followed by secondary wake (pattern III)' materializes. Pattern I is characterized by two steady bubbles forming behind the cylinder. Pattern II features Karman vortex street immediately behind the cylinder, with the vortex street transmuting to two steady shear layers downstream. Inflection angle αi = 32°, 37.5° and 45° are identified for AR = 0.25, 0.5 and 0.75, respectively, where the wake asymmetry is the greatest. The αi effectively distinguishes the dependence on α and AR of force and vortex shedding frequency at either ReD. In Pattern III, the Karman street forming behind the cylinder is modified to a secondary vortex street. At a given AR and α, ReD = 150 renders higher fluctuating lift and Strouhal number than ReD = 100.

Keywords

Acknowledgement

The authors wish to acknowledge the support given by the National Natural Science Foundation of China through Grants 11672096, 91752112 and 11872018 and by Research Grant Council of Shenzhen Government through grant JCYJ20180306171921088.

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