The ultra-low Reynolds number airfoil wake |
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Authors: | Md Mahbub Alam Y Zhou H X Yang H Guo J Mi |
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Institution: | (1) Department of Mechanical Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong;(2) Department of Building Services Engineering, The Hong Kong Polytechnic University, Kowloon, Hong Kong;(3) School of Aeronautical Science and Engineering, Beijing University of Aeronautics and Astronautics, Beijing, China;(4) College of Engineering, Peking University, Beijing, China |
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Abstract: | Lift force and the near wake of an NACA 0012 airfoil were measured over the angle (α) of attack of 0°–90° and the chord Reynolds
number (Re
c
), 5.3 × 103–5.1 × 104, with a view to understand thoroughly the near wake of the airfoil at low- to ultra-low Re
c
. While the lift force is measured using a load cell, the detailed flow structure is captured using laser-Doppler anemometry,
particle image velocimetry, and laser-induced fluorescence flow visualization. It has been found that the stall of an airfoil,
characterized by a drop in the lift force, occurs at Re
c
≥ 1.05 × 104 but is absent at Re
c
= 5.3 × 103. The observation is connected to the presence of the separation bubble at high Re
c
but absence of the bubble at ultra-low Re
c
, as evidenced in our wake measurements. The near-wake characteristics are examined and discussed in detail, including the
vortex formation length, wake width, spanwise vorticity, wake bubble size, wavelength of K–H vortices, Strouhal numbers, and
their dependence on α and Re
c
. |
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Keywords: | |
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