Combined/simultaneous gust and oscillating blade unsteady aerodynamics

Compressor blade row combined/simultaneous gust and oscillating blade unsteady aerodynamics were experimentally investigated from both forced response and flutter perspectives. This included the individual investigations of gust unsteady aerodynamics and oscillating airfoil unsteady aerodynamics. The effects of steady loading and oscillation amplitude were also studied. This research addressed the validity of the small perturbation assumption and the applicability of the superposition principle inherent in linear unsteady aerodynamic analyses. Gust unsteady aerodynamic forcing functions, experimentally modeled with two perforated plate wakes, had significant vortical and potential components. These vortical gusts satisfied the primary linear theory vortical gust requirements, but not the secondary. The rotor blade surface gust response data were correlated with predictions from two linear analyses LINSUB and SFLOW/LINFLO. Both predictions exhibited good trendwise correlation but poor amplitude correlation. The torsion mode oscillating blade unsteady aerodynamics were investigated utilizing an experimental influence coefficient. technique. Oscillation magnitude and steady loading have a significant effect on both the influence coefficient data and the equivalent all blades oscillating unsteady pressure data. These data correlated better with LINSUB than with LINFLO, particularly at high steady loading. Nonlinear blade unsteady aerodynamic responses were evident for oscillation amplitudes larger than 5$\sp\circ.$ The combined/simultaneous gust and oscillating blade unsteady aerodynamic data established limited applicability of superposition principle at high oscillation amplitudes and high steady loading, with superposition generally leading to underprediction of the unsteady lift but an overprediction of the unsteady moment. The combined/simultaneous gust and oscillating blade unsteady aerodynamics are significantly influenced by the phasing between the gust excitation and the blade motion. Gust-blade motion phase angles leading to a constructive interaction of the gust with the oscillating blade aerodynamics increase the unsteady lift and moment magnitudes with small changes in phase while gust-blade motion phase angles leading to a destructive interaction decrease the lift and moment magnitudes with large changes in phase. Thus, neglecting the aerodynamic damping can lead to serious errors in forced response prediction. Combining a gust excitation with an oscillating blade row can alter blade row aerodynamic stability, depending on the gust-blade motion phase angle