Modal Analysis of the Cycle-to-Cycle Variations Observed in Dynamic Stall

An experiment was conducted on a two-dimensional SC1094R8 airfoil model with the intention of investigating the cycle-to-cycle variations observed in dynamic stall. Unsteady surface pressure measurements were recorded at numerous points along the airfoil surface at specific pitching conditions that displayed more than one preferred reattachment process. Sets of individual cycles that represented the dominant reattachment processes were identified and compared to the phase-average, showing significant differences in pressure distributions and aerodynamic loads. Proper Orthogonal Decomposition was then employed to the unsteady pressure distributions with the intent of isolating the influence of specific modes on the cycle-to-cycle variations. The results indicate that the importance of the modes changes depending on the particular reattachment process observed. Approved for public release: distribution unlimited. Review completed by the AMRDEC Public Affairs Office (PR3 3750, 10 April 2018).