Variability of Rotor Wake Interactions and Airfoil Unsteady Aerodynamics

Multistage interaction effects on rotor blade-to-blade wake variability and the resulting downstream vane row unsteady aerodynamic response are experimentally investigated in a high speed fan stage. Multistaging effects on the rotor wake are quantified by acquiring data over two complete rotor revolutions at each of several IGV clocking positions relative to downstream stationary probes. The resulting downstream vane response data are acquired over a range of steady loading conditions, with both design and off-design operation of the rotor considered. Multistage interactions are shown to significantly affect the rotor wake characteristics and lead to the generation of rogue wakes. The fundamental periodicity of these interactions is one complete rotor revolution due to the unequal number of blades and vanes in the machine. The rotor wake and resultant vane row unsteady aerodynamic response variability are also quantified. Off-design rotor operation results in wakes with the largest variability, on the order of the average velocity deficit. The vane response variability is even more pronounced, being as large as 160% of the maximum average unsteady lift over one blade pass period.