Incidence effects on chordwise bending cascade unsteady aerodynamics

Experiments directed at investigating and quantifying the effects of off-design conditions, including mean how incidence and leading-edge dow separation, on chordwise bending mode unsteady aerodynamics are described. An influence coefficient technique is used wherein a single airfoil in the cascade is oscillated in a chordwise bending mode, accomplished with a piezoelectric crystal-based drive system. The resulting unsteady surface pressures on the oscillating airfoil and its stationary neighbors are measured and the unsteady aerodynamic influence coefficients determined, with the cascade unsteady aerodynamics defined through a vector summation. Unsteady aerodynamic data are obtained over a range of reduced frequency values and mean dow incidence angles, with the effects of steady loading and leading-edge separation examined. Significant effects of mean incidence on cascade unsteady aerodynamics that deviate significantly from linearized theory occur near the leading edge, with the nonlinear region increasing with increasing mean incidence. The large-scale effects of mean incidence on the leading-edge unsteady aerodynamic loading are attributable to both steady loading and suction surface separation.