Skin Friction Measurements on the NASA Hump Model

The skin-friction distribution on a wall-mounted hump model has been obtained using oil-film interferometry. This effort is part of a larger study to provide validation cases for simulations of unsteady flows. The challenges of using oil-film interferometry on this model, including model curvature and close camera proximity, are discussed. Skin-friction measurements are obtained over most of the hump model, including especially high-quality measurements in the separated and reattachment regions. These results highlight the method’s ability to capture a wide range of skin friction including measurements in reverse-flow and high-gradient regions. The wall skin-friction data are shown to complement other experimental data, and the use of independent skin-friction measurements for scaling in wall-bounded flows is emphasized. A comparison with results from several computational simulations of the same flow is presented. The comparison indicates that, for the most part, the computations accurately predict the skin-friction ahead of separation, but fail to predict the reattachment point correctly, and thus the comparison in the separated and recovery regions of the flow is poor. The ability of the skin-friction measurements to pinpoint regions where the computation performs poorly in the near-wall region is also presented. From these results, it is evident that independent skin-friction measurements should be a part of all validation experiments conducted in wall-bounded flows.