Incidence effects on chordwise bending cascade unsteady aerodynamics

Experiments directed at investigating and quantifying the effects of off-de sign conditions, including mean how incidence and leading-edge dow separati on, on chordwise bending mode unsteady aerodynamics are described. An influ ence coefficient technique is used wherein a single airfoil in the cascade is oscillated in a chordwise bending mode, accomplished with a piezoelectri c crystal-based drive system. The resulting unsteady surface pressures on t he oscillating airfoil and its stationary neighbors are measured and the un steady aerodynamic influence coefficients determined, with the cascade unst eady aerodynamics defined through a vector summation. Unsteady aerodynamic data are obtained over a range of reduced frequency values and mean dow inc idence angles, with the effects of steady loading and leading-edge separati on examined. Significant effects of mean incidence on cascade unsteady aero dynamics that deviate significantly from linearized theory occur near the l eading edge, with the nonlinear region increasing with increasing mean inci dence. The large-scale effects of mean incidence on the leading-edge unstea dy aerodynamic loading are attributable to both steady loading and suction surface separation.