The present study experimentally investigates a NACA 65-410 cambered airfoil under oscillating motions at moderate Reynolds number. Two oscillation frequencies were tested, which corresponded to a reduced frequency factor, below and above that representative of dynamic stall (i.e. kr > 0.05). Effects of the oscillation frequency, oscillation amplitude as well as the mean oscillation angle of attack on the far-field noise and near-field surface pressure fluctuations were examined. In general, an increase in both the oscillation amplitude and frequency results directly an increase in the far-field noise of an oscillating airfoil, at relatively high mean angles of attack. From the near-field pressure measurements, the surface pressure fluctuations are seen to be either comparable or consistently higher for the oscillating airfoil, as compared to its static counterpart, consistent with previous findings. Moreover, a detailed coherence results along the chord-wise direction reveals that while the coherence increases and spreads towards the leading-edge at low mean angles of attack, it reduces when the flow begins to separate from the airfoil. Short-time Fourier transform analyses of the oscillating airfoil show that for the separated flow conditions, the energy contents are concentrated in the low frequency regions throughout a full oscillation cycle.
|Title of host publication||AIAA Aviation Forum 2020|
|Publisher||American Institute of Aeronautics and Astronautics Inc. (AIAA)|
|Publication status||Published - 15 Jun 2020|
- Oscillating aerofoil acoustics
- NACA 65-410
- Dynamic stall