USE OF THE POLAROGRAPHIC METHOD TO MEASURE WALL SHEAR-STRESS

The measurement of the current to a small polarized electrode mounted flush to the wall allows the determination of the local velocity field closer to a surface than any other method. This technique has found use in measuring wall shear stresses in boundary-layer flows and in studying the structure of turbulence in the viscous sublayer. The interpretation of measurements in the wake behind a cylinder or behind a large amplitude wave is not clear because large amplitude flow oscillations make present analysis of the performance of these electrodes inapplicable. Recent numerical work on the inverse mass transfer problem seems to offer an approach that can handle measurements in these difficult flows.