Variations in Upstream Vane Loading With Changes in Back Pressure in a Transonic Compressor

Dynamic loading of an inlet guide vane (IGV) in a transonic compressor is characterized by unsteady IGV surface pressures. This pressure data was acquired for two spanwise locations at a 105% speed operating condition, which produces supersonic relative Mach numbers over the majority of the rotor blade span. The back pressure of the compressor was varied to determine the effects from such changes. Strong bow shock interaction was evident in both experimental and computational results. Variations in the back pressure have significant influence on the magnitude and phase of the upstream pressure fluctuations. The largest unsteady surface pressure magnitude, 40 kPa, was obtained for the near stall mass flow condition at 75% span and 95% chord. Radial variation effects caused by the spanwise variation in relative Mach number were measured. Comparisons to a two-dimensional non-linear unsteady blade/vane Navier-Stokes analysis shows good agreement for the 50% span results in terms of IGV unsteady surface pressure. The results of the study indicate that significant non-linear bow shock influences exist on the IGV trailing edge due to the downstream rotor shock system.