Parametric Study of the Pressure Stability on an Oscillating Airfoil From Stable to Stalled Flow Conditions

Abstract

This paper presents investigations on the suction side of an oscillation blade at an inlet Mach number of 0.5, with oscillation frequencies from 60 to 210Hz, mean incidence angles from 0° to 10° and with blade amplitudes up to 4.2° (for 60Hz). The time-dependent pressures show that the aerodynamic loads are not linear for the stall region. It was found that an increased mean incidence caused a higher excitation of the blade from the aerodynamic forces, while the effects of varying the blade amplitudes and frequencies were more difficult to determine. At 6° mean incidence, and below, increased blade amplitude for a constant frequency caused the blade suction surface to experience an increased excitation, while for the 7° incidence, and above, the opposite was shown. The fact that the blade amplitude dependence changes when the mean incidence increases above the steady state stall angle is explained by the increased portion of the oscillation cycle spent at stalled conditions. A shift in phase was seen for the highest investigated frequency, which might be due to a phase lag between the blade motion and the leading edge vortex, increasing with increasing frequency.