Characterization of Transitional, High-Enthalpy Boundary Layers on a Blunted Cone. Part II: FLDI and Higher Order Spectral Analysis

Abstract

FLDI is used to characterize an unstable boundary layer on a 5-degree cone. Results from two experiments are presented: shot 2990 represented a high-enthalpy condition with a 2 mm nosetip and shot 2955 represented a moderate-enthalpy condition with a 5 mm nosetip. For shot 2990, the measured frequency of the second-mode instability using FLDI agreed well with the results obtained using schlieren for an experiment performed at similar conditions, and was in good agreement with the maximum N factor frequency obtained using stability analysis. Cross-bicoherence analysis of the FLDI data revealed several sum and difference interactions which contributed to the generation of the first and second harmonics of the second mode within the boundary layer as well as provided the mechanism of energy exchange between the second mode and the mean flow.

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