Extraction of skin friction topology of turbulent wedges on a swept wing in transonic flow from surface temperature images

This paper describes a first-order approximate method of extracting the skin friction topology of turbulent wedges from temperature sensitive paint (TSP) images on a NASA Common Research Model with Natural Laminar Flow (CRM-NLF) wing at Mach 0.85 in the National Transonic Facility (NTF) for full-flight Reynolds number testing. The extracted skin friction topology of a typical turbulent wedge exhibits the similarity in the distributions of the surface temperature, skin friction magnitude and skin friction divergence. The developed method computes a normalized skin friction field associated with a surface temperature variation superposed on a simple known base flow. The selection of the relevant parameters in the application of this method is discussed, including the base-flow power-law exponent, relative amplitude of the surface temperature variation to the base flow, Lagrange multiplier, spatial resolution, and filter size. Graphic abstract Surface temperature and skin friction fields of a typical turbulent wedge: (a) temperature, (b) skin friction magnitude, and (c) skin friction divergence. The color bar has no unit.