Design, Test and Validation of a Probe for Time-Resolved Measurement of Skin Friction

A probe for wall shear stress measurements in nominally 2-D flows has been developed and tested. In contrast to most existing methodologies for skin friction measurement, this probe may be used in non-canonical flows and provides a frequency response suitable for the study of unsteady flow behaviours. The probe consists essentially of two electrically heated parallel hot wires across a small cavity and has the capability to measure the absolute value and the direction of the wall shear stress. The calibration procedure is presented together with results regarding the loss of precision deriving from anomalous positioning of the probe. Applications to a channel flow, to the flow over an oscillating plate and to the flow downstream of a back facing step are shown and compared to results obtained with other techniques in order to validate the probe.