Evaluation of Three Techniques for Wall-Shear Measurements in Three-Dimensional Flows

Recent improvements in three techniques for measuring skin friction in two- and three-dimensional turbulent wall-shear flows are pre-sented. The techniques are: oil-film interfer-ometry, hot-wires mounted near the wall, and surface hot-film sensors based on MEMS tech-nology. First, we demonstrate that the oil-film interferometry technique can be used to measure the skin friction magnitude and its direction in two and three-dimensional wall-shear flows. Secondly, a simple method is outlined to measure the skin friction with a wall-wire located outside of the laminar sub-layer in the same flows. Finally, a system-atic study of the parameters influencing wall-friction measurements with MEMS sensors is presented. The results demonstrate that ac-curate measurements of the mean skin friction with MEMS sensors are possible in two and three-dimensional wall flows. Measurements by the three techniques are compared to each other and with past measurements in the same facility