Acta Mechanica

, Volume 149, Issue 1–4, pp 135–147 | Cite as

Aerodynamic properties of a wing performing unsteady rotational motions at low Reynolds number

  • S. L. Lan
  • M. Sun
Original Papers


The aerodynamic forces and flow structures of a wing of relatively small aspect ratio in some unsteady rotational motions at low Reynolds number (Re=100) are studied by numerically solving the Navier-Stokes equations. These motions include a wing in constant-speed rotation after a fast start, wing accelerating and decelerating from one rotational speed to another, and wing rapidly pitching-up in constant speed rotation. When a wing performs a constant-speed rotation at small Reynolds number after started from rest at large angle of attack (α=35°), a large lift coefficient can be maintained. The mechanism for the large lift coefficient is that for a rotating wing: the variation of the relative velocity along the wing-span causes a pressure gradient and hence a spanwise flow which can prevent the dynamic stall vortex from shedding. When a wing is rapidly accelerating or decelerating from one rotational speed to another, or rapidly pitching-up during constant speed rotation, even if the aspect ratio of the wing is small and the flow Reynolds number is low, a large aerodynamic force can be obtained. During these rapid unsteady motions, new layers of strong vorticity are formed near the wing surfaces in very short time, resulting in a large time rate of change of the fluid impulse which is responsible for the generation of the large aerodynamic force.


Vortex Reynolds Number Vorticity Aerodynamic Force Wing Surface 
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Copyright information

© Springer-Verlag 2001

Authors and Affiliations

  • S. L. Lan
    • 1
  • M. Sun
    • 1
  1. 1.Institute of Fluid MechanicsBeijing University of Aeronautics and AstronauticsBeijingP. R. China

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