SINOPSIS

A comparison between the turbulent flows in a smooth and two different rough wall channels is reported. It is demonstrated that even though the outer layer may appear to be unaffected by the surface conditions, since the mean velocity defect profiles are very similar, modifications to the turbulent stresses as far out as y/h ~ 0.3 are found. Closer to the wall the contributions from the fourth quadrant are found to be much more dominant in the rough cases than over the smooth wall, confirming earlier findings that surface roughness tends to stimulate sweep type of motions. A velocity dependent effective angle method for the calibration of yaw-response of hot-wire X-probes at low velocities is presented. Comparisons with DNS (Moser et al., 1999) show that this approach significantly improves estimates of Reynolds stresses at low velocities compared to the conventional method assuming a fixed effective angle.