The viscosity balance method of skin friction measurement: further developments including applications to three-dimensional flow

Abstract

The application of oil film interferometry to the measurement of skin friction in air flow was described in an earlier paper by Tanner and Blows (see ibid., vol.9, no.4, p.194 (1976)). This work is extended in various ways. These include use of oil droplets as an alternative or in addition to continuous films, particularly for exploration of three-dimensional flows. The use of accidentally or deliberately introduced disturbances as streamline markers is described. The use of the characteristics method to follow transient changes of oil film profile is demonstrated. Many checks on the consistency of the methods and comparisons with theory are given. The results suggest that the methods can give a wealth of information concerning surface flows which would otherwise be difficult, if not impossible, to achieve.