A skin-friction measurement technique is proposed and demonstrated. The technique uses a distributed luminescent oil-film over the region of interest The thickness of the oil-film is measured by ratioing the luminescent signal from the fluorescent oil with the incident light from the excitation source which is scattered from the surface. The velocity distribution within the oil-film is revealed by tagging photochromic molecules in the oil. The tagged molecules can be followed and are used to measure the oil-film's velocity distribution. The velocity of the surface of the oil-film, ν_h, and the oil-film thickness, h, are used to determine skin-friction, which is given as τ = (μ_0ν_h)/h, where μ_0 is the oil-film viscosity. As a preliminary test, this technique is used to determine skin-friction values on a NACA 66-215. The results are compared with those from interferometric oil-film methods (FISF) and are shown to be encouragingly close.
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