Multiple Aperture Approach for the Study of Large-Scale Boundary-Layer Structures

Abstract

An investigation of large-scale boundary layer structure using two simultaneously sampled streamwise oriented apertures is presented. Measurements were conducted in Notre Dame’s Tri-Sonic facility at M = 0.5 at varying sampling frequencies and aperture separations. In this paper we investigate the convective nature of boundary layer structures using wavefront sensing techniques and POD analysis. The data has shown that the low order POD modes, corresponding to the larger structures within the flow, mostly convect and do so at a higher convective velocity. Despite the fact that higher order modes only account for $\approx 30$% of the energy in the wavefront, they contribute significantly in the residual wavefront error. For this reason, models beyond a linear, simply convecting model must be developed to accurately make wavefront predictions with separations greater than $3\delta$.