Skin friction measurements in a Mach 6 inlet test

Experimental Investigation of High-Speed Boundary Layers with Wall Roughness

“…The uncertainty of the measurements associated with the skin friction gages has been previously documented at 6%. 25 However, it was found here that alignment for the skin friction gages proved to be a critical factor and increased the estimated uncertainty to approximately 15%. The skin friction was also evaluated with from the velocity profile using (1) the integral method as described in Section 4.1.2 and (2) the velocity gradient method as described in Section 4.2.1.…”

“…The smooth plate floating element skin friction errors have been previously documented. 25 The rough wall skin friction was evaluated with an integral method based on the velocity profile (described in Section 4.1.1), and the uncertaintywas evaluated by perturbing the inputs (6»" 6 and Ax) by the uncertainties listed in Table 3: the uncertainty result is also listed in Table 3. The uncertainty analysis of the laser Doppler velocimetry data accounted for probe volume location, record length, velocity gradient broadening, 27 ' 28 laser beam angular alignment, seed bias, 28 density bias, coincidence filtering and repeatability.…”