Method for Measuring Surface Shear Stress Magnitude and Direction Using Liquid Crystal Coatings (ARC-12052)

In aerodynamics research, much valuable information can be gained from visualizing and measuring shear stress patterns on solid surfaces. Frictional forces generated by gases or liquids flowing over these surfaces can significantly influence the performance of aircraft, ships, or surface-transport vehicles. Internal frictional forces, such as those caused by air compression through a jet engine or blood flow through an artificial heart chamber, also affect aerodynamic or mechanical performance. To date, measuring surface shear stress requires expensive mechanical balances or intrusive probes and sensors. This liquid crystal coating technique developed at NASA Ames is a diagnostic technique that gives rapid visual information and measurements of surface shear stress magnitude and direction over an entire surface in a continuous, non-intrusive manner. A shear-sensitive liquid crystal coating is applied to the test surface, illuminated by a white light source, and the reflected color patterns are recorded using a color video camera. Shear-induced color changes are recorded continuously, with time responses on the order of milliseconds.

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