Luminescent Oil Film Flow Tagging Skin Friction Meter Applied to FAITH Hill

Abstract

The luminescent oil film flow tagging skin friction meter is presented and used to collect time-averaged spatially distributed skin friction data on the surface of NASA’s FAITH model. The technique estimates skin friction by monitoring the evolution of a luminescent oil film evolving under the influence of skin friction, pressure gradients, and gravity. The thickness distribution of the oil film, , and the velocity of the surface of the oil film, , are measured experimentally, and the dynamic viscosity of the oil, , is taken from the oil manufacturer or is determined through calibration. Then, skin friction is estimated as . The thickness distribution of the oil film is measured by ratioing the intensity of the luminescent signal from the fluorescent oil with the intensity of the incident light that is scattered from the surface of the model. The resulting quotient is independent of the intensity of the incident light and directly proportional to the thickness of the oil film. The velocity of the surface of the oil film is measured by tagging and following photochromic molecules in the oil film. The new luminescent oil film flow tagging skin friction data compare well with fringe image skin friction data. Also, an experimental study is conducted to determine the extent to which it is appropriate to neglect the effects of a pressure gradients and gravity when determining skin friction from the evolution of an oil film. Results are presented supporting that this approximation is appropriate for a sufficiently thin film of oil or for a sufficiently high skin friction magnitude.