Skin friction measurements on reflective surfaces using nematic liquid crystal

A new liquid crystal technique for full surface skin friction measurements is introduced. With the new technique, the transmission of light through ne matic liquid crystal viewed in reflection provides a quantitative measureme nt of the skin friction. The measurement technique is discussed with the ai d of a model which describes the rotation dynamics of the liquid crystal mo lecules. Calibration experiments performed in a laminar flow duct demonstra te that the model captures the essential physics of the new technique. The measurement of skin friction downstream of a three dimensional roughness el ement in an incompressible laminar boundary layer is then presented as a de monstration of the utility of the technique.