DOI: 10.1615/TSFP3
FLOW PAST AN OSCILLATING BI-CONVEX AEROFOIL
RÉSUMÉ
This preliminary study aims to investigate the flow
structure of an impulsively started bi-convex aerofoil, both at fixed incidences as well as in oscillation, using a digital cross correlation particle image velocimetry (PIV) technique. The experiments are conducted in a recirculating, piston (water) tunnel and the angular amplitude as well as the reduced frequency are varied for a given Reynolds number and linear acceleration.
The results of the experiments show that for the static case, an increase in the angle of attack intensifies the instabilities within the flow whilst for the oscillating cases, the reduced frequency, rather than the angular amplitude, is the key parameter which influences the fundamental characteristics of the flow.
The lower reduced frequency cases display characteristics
that are remarkedly similar to that of the static stall cases, with the main distinction being a chronological delay in the flow evolution characteristics that exists between the former and the latter at any particular angle of attack.
The higher reduced frequency cases, on the contrary, are set apart from the other cases in both leading edge and wake development. The leading edge activity seems to be out of phase with what would normally be predicted in a quasi-steady condition whilst the wake vortex generation is predominantly due to the rotation of the aerofoil rather than the effect of the translating flow, as in the lower reduced frequency cases.