Computational aerodynamics of oscillating cascades with the evolution of stall

The applicability of the vortex method to cascades of oscillating airfoils is assessed by computing the unsteady incompressible lift, drag, and moment for small incidence, thickness, and vibratory displacement—the so-called “classical” case. The results for a limited sampling of cascade geometries, reduced frequencies, vibration amplitudes, and interblade phase angles are in excellent agreement with available analytical results. Instantaneous streamline patterns and discretized vorticity distributions are presented as an aid in physical understanding. The importance of the interblade phase angle as a governing parameter is confirmed. Then the effects of mean incidence, vibration amplitude, and stagger angle are studied. Important new results are presented showing the evolution of the classical reactions into the stalled-flow reactions with incidence, frequency, and amplitude as parameters. In particular, the complicated interaction is demonstrated between the structural frequency of the blades (considered as one of the “inputs” to a nonlinear aeroelastic system) and the output frequency spectrum of the aerodynamic reactions. The implications for future direction of research and design code implementation are discussed.