Near-wall velocity measurements in two-dimensional turbulent boundary layers

Significant differences involving near-wall velocity profiles in two-dimensional turbulent boundary layers when such data was plotted on law of the wall coordinates were reported by D. Coles in the Stanford Conference. These discrepancies can be especially important when near-wall velocity data is used to infer the local wall shear stress from law of the wall similarity laws. With emphasis on the near-wall measurements, this study systematically investigated the effects of the following parameters on the velocity profile: probe type (straight-stem claw probe, gooseneck probe, and hot-wire probe), probe tip diameter, streamwise pressure gradient, and boundary layer tripping. In addition, the local wall shear stress was inferred from the near-wall data, and the effects from the previously mentioned parameters and the choice of both the law of the wall constants and formulas on the inferred wall shear stress were examined.