Coating provides visualization of surface shear stress rapidly

In order to assist rapid, nonintrusive analysis of surface shear stress, NASA's Ames Research Center has developed a liquid crystal coating technique that provides researchers with rapid visual information and measurements.

NASA scientists rely on information obtained in aerodynamic research to design new, improved structures. "The Liquid Crystal Coating Method for Measuring Surface Shear Stress Patterns" provides a method for visualizing and measuring the magnitudes and directions of continuous aerodynamic surface shear stress vector distributions. Time response of the coatings is on the order of a millisecond. This method immediately reveals the cause and effect relationships among changes in model configuration or test environment and the resulting surface shear field. The results obtained by this method, when properly calibrated, reflect an accuracy equivalent to that of existing point measurement sensors.

To start, the test surface gets an application of a shear-sensitive liquid crystal coating, which is then illuminated by a white light source and observed at multiple viewing angles, Application of aerodynamic shear to the surface layer of the liquid crystal coating causes the molecules in the coating to align. These molecules then scatter white light into a spectrum of colors with different orientations to the surface that a video camera can record.

This nonintrusive method does not require any surface penetration or flow disruption. Further, the only optical access required by this technique is for illumination and video camera recording. Testers can also use this method in conjunction with force and moment balances.

The potential applications of this technology include wind tunnel testing of aircraft and components, wind tunnel testing of automotive designs, track testing of race cars, wind tunnel testing of missiles, and water tunnel testing of racing yachts. This technology may transfer to a commercial product line without modification. The coatings employed by this technique are commercially available at a cost of less than $20 per square foot of surface. NASA is now seeking partners to license this technology.

For more information on this NASA technology, contact John Bacon, MTAC/ISA liaison, at (412) 383-2530; fax (412) 383-2595; or jbacon@mtac.pitt.edu.