The Effect of IGV Wake Impingement on a Rotor Boundary Layer

Abstract

This paper examines the response of a rotor boundary layer on a rotor blade to an impinging wake of an Inlet Guide Vane (IGV) located upstream of this blade. High resolution two-dimensional Particle Image Velocimetry (PIV) measurements are conducted in a refractive index matched facility that provides an unobstructed view of the entire flow field. Analysis of data obtained at several rotor phases enables us to examine the changes in the boundary layer structure as the rotor blade dissects the impinging wake. We focus on the suction side boundary layer near the trailing edge of the blade, in regions with adverse pressure gradients. The results show that during wake impingement the boundary layer becomes significantly thinner, and has a more stable profile compared to other phases at the same location. We measure the phase-averaged momentum and displacement thicknesses, and show that they indeed decrease in the regions impinged by the wake. In an attempt to explain this trend, we examine different terms in the integral momentum equation that can be determined from planar PIV data. The results show that the phase-averaged unsteady term is a primary contributor to the decrease in momentum thickness within the impinging wake, and that the terms involving Reynolds stresses are small. Curvature effects play a significant role in the analysis. The estimated Coriolis force is small but not negligible.