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A flight test investigation was conducted to evaluate an infrared (IR) imaging technique to visualize off-surface flow phenomena. A single-engine, general-aviation airplane was equipped with an IR imaging system that viewed the region around the left wingtip. Vortical flow at the wingtip was seeded with sulfur hexafluoride, a gas with strong infrared absorbing and emitting characteristics. Different terrain and sky backgrounds were evaluated for their effect on IR images of vortical flow. The best IR images were obtained with a clear sky background. The results of the investigation indicate that IR flow visualization compliments existing smoke generator methods for off-surface flow visualization.

The ability of modern airplane surfaces to achieve laminar flow over a wide range of subsonic and transonic cruise flight conditions has been well-documented in recent years. Current laminar flow flight research conducted by NASA explores the limits of practical applications of laminar flow drag reduction technology. Past laminar flow flight research focused on measurements of transition location, without exploring the dominant instability(ies) responsible for initiating the transition process. Today, it is important to understand the specific causes(s) of laminar to turbulent boundary layer transition. This paper presents results of research on advanced devices for measuring the phenomenon of viscous Tollmien-Schlichting (T-S) instability in the flight environment. In previous flight tests, T-S instability could only be inferred from theoretical calculations based on measured pressure distributions.