The Effects of Blade-Row Spacing on the Flow Capacity of a Transonic Rotor

Abstract

Results from the ongoing Air Force Stage Matching Investigation are presented. In the present work the effect of upstream blade row wakes on the flow capacity of a downstream stage (where the rotor sets the choking flow) is investigated. An embedded stage was simulated by placing a set of wake generators (similar to inlet guide vanes) in front of a highly loaded single stage transonic core compressor. The wake generator-to-rotor axial spacing was varied in addition to the vane count. A complete parametric test matrix was completed in order to determine which parameters were important to the choking flow capacity. The results show that for axial spacings above 50% of the upstream axial blade chord, simple wake mixing alone fully accounts for the upstream flow losses and a simple mass flow rate correction based on the rotor face mass averaged total pressure is sufficient. At spacings closer than this, other effects or loss mechanisms may be present. If these loss sources do exist, they are of unknown origin and magnitude and so an embedded overflow condition for these spacings cannot be ruled out. Research is ongoing that will attempt to identify and clarify the relevant details associated with these close blade row spacings.