Vortical forcing function variations with axial spacing and blade count

Abstract

The aerodynamic forcing function experienced by a compressor rotor is investigated by a series of fundamental experiments in a high speed turbomachinery facility. Data is acquired and analyzed to determine the forcing function generated by an inlet guide vane (IGVs) row, in particular, the effect of variations in axial spacing and blade count is investigated. The research compressor facility is comprised of an IGV row upstream of a rotor/stator stage. A circumferential traverse assembly is inserted between the IGV and rotor/stator stage, thereby allowing measurements to be made across several IGV wakes. For an IGV relative Mach number of 0.53, measurements of the IGV wake velocity fields for three axial spacings with 24 and 40 IGV blades are made. After Fourier decomposition, a vortical gust analysis is implemented to determine the vortical wake gust forcing functions upstream of the rotor. Significant higher harmonic content is evident in the vortical gust forcing functions for both the 24 and 40 IGV cases with the high harmonics decaying at a uniform rate due to viscous diffusion, while the first harmonic remains relatively constant. Increasing the number of IGV blades increased the magnitude of the unsteady vortical forcing function by introducing more blade blockage. In addition, the decay rate of the higher vortical forcing function harmonics increased with increasing numbers of IGV blades.