Skin Friction from Surface Scalar Visualizations

This chapter describes extraction of a skin friction field from surface scalar visualizations with pressure sensitive paint (PSP) as an oxygen sensor and sublimating coatings. First, the exact relation between skin friction and surface scalar concentration is derived from the binary mass transport equation for an incompressible flow on a curved surface, and further the specific forms of this on-wall relation are formulated for its applications in several surface scalar visualizations. Then, the variational method is developed to determine a skin friction field from surface scalar visualization images when the source term is modeled (approximated). As examples, the approximate method is applied to PSP visualizations of nitrogen impinging jets and surface luminescent dye visualizations of delta wings in water flows.