A set of inlet guide vane (IGV) unsteady surface pressure measurements is presented. The unsteady aerodynamic effects of a highly loaded, high speed downstream compression stage on the upstream inlet guide vane/stator surface pressures are characterized by experimental analysis methods. The axial spacing between the IGV and rotor was varied between 12%, 26%, and 56% of the rotor chord for a 105% speed near stall operating condition, which is transonic. Unsteady IGV surface pressures were acquired for two spanwise locations on both blade surfaces. Variations in axial spacing have significant influence on the magnitude and phase of the upstream pressure fluctuations. The largest unsteady surface pressure magnitude, 49.6 kPa, was obtained for the 12% axial spacing configuration at 75% span and 95% chord. Spanwise variation effects caused by the increased relative Mach number were measured. The upstream bow shock effect is strongly non-linear in character. The results of the study indicate significant variations in the IGV unsteady loading caused by axial spacing variations.
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