Oil film interferometry (OFI) is a measurement technique used to evaluate local wall shear stress and limiting streamline direction. It has been applied to aircraft wings in wind tunnel testing and in turbine cascade testing. The accuracy of the technique is largely dependent on the analysis of interferograms. A new technique for interferogram analysis is presented that is simple and particularly well suited to analyzing interferograms characterized by few fringes. For example, limited fringe definition can occur from dust contamination on the pressure surface of turbine airfoils during cascade wind tunnel testing. The new technique is described and illustrated with examples.

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