Modern developments in shear-stress measurement

This paper reviews three relatively modern categories of skin-friction measurement techniques that are broadly classified as microelectromechanical systems (MEMS)-based sensors, oil-film interferometry and liquid crystal coatings. The theory, development, limitations, uncertainties. and misconceptions of each of these techniques are presented. Current and future uses of the techniques are also discussed. From this review, it is evident that MEMS-based techniques possess great promise, but require further development to become reliable measurement tools. Oil-film techniques have enhanced capabilities and greater accuracy compared to conventional shear-stress measurement techniques (i.e.. Preston tube, Clauser plot, etc.) and, as a result, are being employed with increasing frequency. Liquid crystal coatings are capable of making measurements of mean shear-stress vector distributions over a region of a model, but complex calibration and testing requirements limit their usefulness. (C) 2002 Elsevier Science Ltd. All rights reserved.