ABSTRACT
The combined effect of the length-to-height ratio and Reynolds number upon the recovery of the axial velocity in the wake of roughness element is rather complicated. Figure 53 shows the vertical profile of the velocity defect (velocity deficit at that height from the undisturbed velocity at the same height) as a function of axial location from the roughness element, length-to-height ratio of the roughness element, and Reynolds number obtained from different investigations [117,122,127,128]. For Ll H = 3, the defect at higher Reynolds number seems to be higher at XI H = 10. However, for Ll H = 9 and oo, the velocity defect is lower for higher Reynolds number. This result should be accepted with caution, as sufficient data are not available for further understanding of this phenomenon.
