In this paper, a method for measuring the instantaneous shear-stress distribution over a solid surface in a fluid flow is studied by using a surface-flow visualization technique with a shear-sensitive liquid-crystal coating. The colour response of the liquid-crystal coating is calibrated against the various shear-stress magnitudes and directions with an experimental test section of laminar channel flow. The measurement of instantaneous shear-stress distribution is carried out using two colour CCD cameras, which are situated side by side in stereoscopic arrangement. The colour-to-shear-stress transformation is conducted by analysing the hue distribution of the visualized colour image with the calibrated relationships between the hues from the two colour CCD cameras and the shear-stress magnitude and direction. The usefulness of this technique was demonstrated by the measurement of shear-stress distribution around a circular cylinder on a surface under decelerating flow conditions.

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The shear-stress measurement by liquid-crystal visualization was extended to the flow

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