High Resolution Boundary Layer Measurements on a Wing-Fuselage Model

A persistent problem in boundary layer experiments has been the inability to experimentally measure close enough to the wall the resolve the near wall region. This can be because a physical probe, like a hot wire anemometer, is larger than the near wall scales or because an optical probe, like laser Doppler velocimetry, lacks the resolution to get close enough to the wall. A variation on particle image velocimetry (PIV), has been developed by one of us (Willert), where a long-range micro PIV setup is used to resolve down to sub-layer scales in a turbulent boundary layer. This type of micro PIV setup was used on a semi-span wing-fuselage model to measure the boundary layer on the fuselage ahead of the wing at Re_\theta up to 2700, where the sub-layer could be characterized down to y^+ \approx 1. Since this is a PIV based technique, the measurement includes not just the mean profile, but also the variance and co-variance terms. The extension of the profile into the sub-layer means that the wall shear stress can be directly checked against the Clauser method. This talk will include an overview of the technique and challenges of implementing it in this setting, as well as preliminary results from wind tunnel testing