Method for determing shear direction using liquid crystal coatings

A method of determining the direction of shear stresses imparted to a liquid crystal coating by subsonic or supersonic fluid flows past the surface of the coating, said method comprising:

• directing a beam of white light at an oblique angle with respect to the surface of the liquid crystal coating so as to cause said white light to be reflected from said surface in a color spectrum comprising bands of different colors at different angular positions in a fixed angular sequence;
• calibrating the method by arranging an observer at a selected acute angle with respect to the surface of the coating and determining the color band observed by the observer at that angle under conditions wherein no shear stresses are applied to the coating to thereby establish a reference color band;
• determining the reflected color band observed by the observer at said selected acute angle when shear stresses are imparted to the surface of the liquid crystal coating;
• and
• determining the direction of said shear stresses based on the rotational direction of the observed color band relative to the reference color band.

A method of determining the direction of shear stresses imparted to a liquid crystal coating by supersonic injector flow past the surface of the coating in a wind tunnel facility, said method comprising:

• directing a beam of white light at an oblique angle with respect to the surface of the liquid crystal coating so as to cause said white light to be dispersed from said surface in a color spectrum comprising bands of different colors at different angular positions in a fixed sequence comprising blue, green, yellow and red bands;
• calibrating the method by arranging a observer at a selected acute angle with respect to the surface of the coating so that the green color band is observed by the observer at that angle under conditions wherein no shear stresses are applied to the coating;
• and
• determining whether the reflected color band observed by the observer at said selected acute angle when shear stresses are imparted to the surface of the liquid crystal coating is (i) a blue band indicating counter-clockwise rotation of the spectrum and that the shear direction is to the right or (ii) is a yellow or red band indicating clockwise rotation of the spectrum and that the shear direction is to the left, so as to thereby determine the direction of said shear stresses based on the rotational direction of the observed color band relative to the green color band.