Measured Rotor Wake and Potential Forcing Functions, Including Blade Row Interactions

A fundamental experiment is directed at the acquisition and analysis of data defining compressible forcing functions generated by a rotor, including interactions with the upstream-generated inlet guide vane (IGV) wakes, for application to wake forcing function models in turbomachine forced-response design systems. The research fan facility consists of an IGV row and a downstream rotor. IGV-rotor axial spacing is variable, with the IGV row able to be indexed circumferentially, thereby enabling the rotor wakes to be measured both in the IGV freestream and wakes. At a rotor-relative Mach number of 0.6 unsteady measurements are made of the rotor wake pressure and velocity fields for two IGV-rotor axial spacings and with the rotor wake measured in the IGV freestream and wake regions. The decay characteristics of the rotor blade wakes are compared to empirical correlations. After Fourier decomposition, a vortical-potential gust splitting analysis is implemented and applied to the first-harmonic data to determine the vortical and potential harmonic wake gust forcing functions both upstream and downstream of the rotor. The potential gust component of the rotor wakes upstream of the rotor is found to be dominated by the first-harmonic component with small contributions from the second and third harmonics. Higher harmonics of the vortical gust component of the rotor wakes measured both in and out of the IGV wakes are found to be significantly reduced in the IGV wake regions. (Author)