Technology Commercialization Opportunity

Method For Measuring Surface Shear Stress Magnitude And Direction Using Liquid Crystal Coatings

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. The National Aeronautics and Space Administration now seeks partners to license the Liquid Crystal Coating method for measuring Surface Shear Stress Patterns.

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.

Technical Basics

Molecules within a shear-sensitive liquid crystal coating scatter white light as a spectrum of colors, with each color having a different orientation relative to the surface. Under normal illumination, any surface point exposed to a shear vector directed away from the observer exhibits a color change, with the color shift being a function of shear magnitude and direction relative to that observer. Conversely, if the shear vector is directed toward the observer, thecoating exhibits no color change and appears as a rust or brown color, independent of shear magnitude and direction. Based on these results, a full-surface shear stress visualization and measurement method, involving multiple oblique-view observations of the test surface, was formulated, successfully demonstrated, and patented.

Technology Commercialization Status

Licensing opportunities are available for U.S. companies interested in commercial applications of these inventions.The measurement capabilities are described in U.S. Patent #5,438,879 entitled "Method for Measuring Surface Shear Stress Magnitude and Direction Using Liquid Crystal Coatings" and the flow-visualization capabilities are described in U.S. Patent #5,394,752 entitled "Method for Determining Shear Direction Using Liquid Crystal Coatings" issued to Dr. Daniel C. Reda, and assigned to NASA.

Potential Commercial Uses

• Wind tunnel testing of aircraft and components, such as wings and control surfaces.
• Wind tunnel testing of automotive designs.
• Track testing of race cars.
• Wind tunnel testing of missiles.
• Water tunnel testing of racing yachts.
  

Benefits of Technology

• Non-intrusive: No requirements to penetrate the surface or disturb the flow.
• Ease of set-up: Optical access required only for illumination and video camera recording.
• Inexpensive: Coatings are less than $10/square foot of surface and are commercially available.
• Immediate full-surface results: Method immediately reveals cause-and-effect relationships between changes in model configuration or test environment and the resulting surface shear field.
• Compatibility: Method can be used simultaneously with force and moment balances.
• Fast response time: One millisecond response to changing conditions.
• Accuracy: When properly calibrated, accuracy is equivalent to that of existing point-measurement sensors.