Rotor Wake Variability in a Multistage Compressor

Abstract

Rotorwakevariability isnot typically accountedforin computational fluid dynamics models,yet small deviations from the modeled average wake could have impacts on performance and forced vibratory response of airfoils. This paper quantifies rotor wake variability, in terms of wake depth and width, for each stage in a three-stage research compressor. Time-resolved flow angle data are acquired with a cross-film sensor at midspan for all three rotor exits for 50 circumferential positions spanning a vane passage. This research focuses on rotor wake variability driven by blade row interactions. The scope of the study includes wake variations caused by blade-to-blade differences, interactions with upstream rotor wakes, and interactions with the potential field of the downstream vane row. The lowest levels of variability are associated with rotor 1. In the downstream rotors, ensemble-averaged revolutions of data show an amplitude modulation caused by interactions with the rotor wakes from the upstream blade rows and, thus, increased levels of blade-to-blade wake variability. The main effect of the downstream vane row is to shift the mean levels of the wake without significantly influencing the wake shape. Nomenclature mc = corrected mass flow rate Nc = corrected rotational speed R = rotor Rec = Reynolds number based on chord length S = stator t = time U = wheel speed V = flow velocity in the absolute reference frame W = flow velocity in the rotating reference frame � = absolute flow angle � = relative flow angle � = adiabatic efficiency � = standard deviation