On the use of Irwin and Preston wall shear stress probes in turbulent incompressible flows with pressure gradients

A set of wall shear stress pressure probes, of the type developed by Irwin and Preston, was tested in a duct flow under various positive and negative pressure gradients. A hot wire wall shear stress probe with temperature compensation was employed as the reference instrument. In the present study, the parameter Δ used by Patel to quantify the severity of the pressure gradient was made to vary between −0.035 and 0.05, thus extending the range of results available in the literature. The experimental facility constructed allowed the probes to be calibrated and tested without changing of position, as well as obtaining the same value of Δ with different types of flow. It was found that both pressure probes studied had broadly the same behaviour, and that, in the case of positive pressure gradients, the measuring errors produced by the Irwin and Preston probes depended very strongly on the conditions of the flow development. The use of an integral parameter to complement Δ is suggested in order to try to predict the errors produced by the pressure probes under study.