In the near-stall regime, the shedding of coherent structures can result in large unsteady aerodynamic loads. Under such conditions, high-aspect-ratio wings will experience some degree of structural motion. Simulations and experiments for a chord-based Reynolds number of Re = 200;000 are carried out for a wing section with an X-56A airfoil to investigate the effect of a harmonic heaving/plunging motion on the unsteady aerodynamics. The reduced frequency of the structural motion is 0.35 < k < 1.4, and the amplitude is 3.2-9.6% based on chord length. For a plunging motion at a 10 deg mean angle of attack, the unsteady lift is in good agreement with the Theodorsen theory. As the mean angle of attack is increased up to 14 deg, the flow begins to separate intermittently from the suction side of the wing. The onset of flow separation and the shedding of the resultant stall vortex depend on the frequency and amplitude of the structural motion. Steady spanwise disturbances that are introduced at the leading edge are found to strengthen the stall vortex. For a 16 deg angle of attack, the wing section is fully stalled. However, when subjected to a low-amplitude plunging motion, the flow intermittently reattaches and the mean lift is increased.
ASJC Scopus subject areas
- Aerospace Engineering