High accuracy skin friction measurements demonstrated in a wall jet

The demand for high accuracy mean skin friction $C_f$ measurements has increased recently due, in part, to the need to have accurate friction velocities for scaling wall bounded flows. Other areas that will benefit from accurate $C_f$ values are validation cases for computational fluid dynamics and wall-bounded flow control studies. Here we consider a $C_f$ measurement technique capable of high accuracy, oil film interferometry (OFI). Specifically, the steps required for quality measurements in general flows are discussed including image registration and image analysis with a focus on one, two, and multiple image analysis approaches. The methods are applied to interferograms taken in a wall jet flow using OFI, and the results are applied to scaling wall jet velocity profiles obtained using laser Doppler anemometry.