THE EFFECTS OF WALL ROUGHNESS ON THE TURBULENT BOUNDARY LAYER

摘要

The Turbulent flows over a zero-pressure-gradient boundary layer are investigated to observe the effect of a -dimensional wall wavy roughness, perpendicular to the mean flow, and of two -dimensional wall roughness on the organization of the coherent motions characterizing the turbulent flow. article image velocimetry is used to describe instant flow fields in the streamwise plane normal to the wall and in planes parallel to the wall. In the outer layer the organization of coherent motions appears to be very similar to the one observed for the case of a smooth wall. Two-point spatial correlations of the longitudinal and wall normal velocity fluctuations suggest the recurrence of packets of hairpin vortices travelling coherently as expected in a turbulent boundary layer over a smooth wall. The flow velocity correlations enlighten differences in scale and orientation of the structures.