Mapping Skin Friction Fields in Complex Flows Using Luminescent Oil

This paper describes application of a global luminescent oil film skin friction meter to quantitative skin friction diagnostics in complex flows. This meter is developed based on the relationship between the oil film thickness and luminescent intensity of an oil film mixed with a luminescent dye. The projected thin oil film equation is given to relate the normalized luminescent intensity with skin friction. A variational formulation with a smoothness constraint on skin friction is proposed to obtain a snap shot solution from two consecutive images for a relative skin friction field. Then, a complete skin friction field is reconstructed through superposition of a sequence of snap shot solutions. The method is used to map skin friction fields in junction flows and flows over surface roughness elements, delta wings and low aspect ratio wing.