Skin Friction Measurement Technology for Underwater Applications

The measurement of skin friction on hydrodynamic surfaces at high Reynolds numbers is essential for the design of advanced Naval technology. Knowledge of the mean skin friction and flow separation is essential for the validation of computational models and design of advanced maneuvering systems. Unfortunately, the accurate measurement of wall skin friction on complex surfaces under high Reynolds number continues to be problematic. In this proposal we introduce an optical sensor for measurements of mean skin friction on large models that operates in water. This sensor is based on the diffusion of a fluorescent dye from a polymer film into the water, a mass transfer sensor. Mass transfer is determined by monitoring the rate of dye diffusion from the film and applying a transient model to the process. This technique has been demonstrated qualitatively by detecting boundary layer transition on an airfoil model in the 12-inch water tunnel at Penn State University. In the Phase I effort, a series of sensors will be manufactured and tested on a flat plate in the Penn State University water tunnel at Reynolds numbers of up to 9-million. Skin friction results from the new sensor will be compared to established techniques.