The determination of local turbulent skin friction from observations in the viscous sub-layer

Abstract

Observations made in the viscous sub-layer of turbulent shear flows with small surface pitot-tubes and hot wires show that such instruments give accurate values of boundaryiayer skin friction, at least in zero pressure gradient, but only when calibrated in turbulent flow: calibration in laminar flow gives incorrect results by about 10 per cent with u, d/v = 2. It is further shown that the region of universality of turbulent velocity profile is confined to the viscous sub-layer, and an upper limit u, d/v = 30 is suggested for the height d of a flat surface tube if reasonable accuracy is to be obtained in skin-friction measurements.