The dynamics of thin liquid films that develop on a solid surface and are driven by an adjacent gas flow have many engineering applications including fuel systems in internal combustion engines, liquid atomizer systems, refrigerant flows in evaporators, and film drag over wetted surfaces. However, the lack of a reliable, nonintrusive technique to capture and analyze the characteristics of the film limits current efforts to validate models of the film flow. A primary parameter for understanding and predicting the film behavior is the determination of the average film thickness. An interferometric film thickness measurement technique, along with a fast Fourier transform-based postprocessing method, are investigated for use as a diagnostic tool to obtain the average film thickness of these dynamic films in the presence of surface waves. The approach centers on the concept that one single, unique interferometric fringe spacing will exist over an image with a valid film thickness measurement. Important considerations and limitations for accurate measurement of the film thickness are discussed along with experimental results showing the capability of the technique to capture the average thickness of the shear-driven film.
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