EFFECTS OF ROUGH WALL IN FULLY DEVELOPED TURBULENT PIPE FLOW

Hot wire measurement is carried in fully developed turbulent pipe flow which introducing the rough wall sections (containing d- and k-type roughness alternatively) and emphasis on the statistical properties of turbulence for each flows. Sufficient pipe length is provided to ensure for fully recovery after disturbed by rough wall. On comparison, the major differences between d- and k-type rough wall effect could be found in early response region (x/D = 0.1 to 4). The violent ejection from the k-type roughness is found to the large effect to the main flow which turns into larger additional turbulent energy production. The changing of wall friction could increase the local shear stress which leads to the formation of stress bore but depends on the amount of changes. This stress bore is found to propagate from the vicinity of the wall to the pipe center which does not depend on type or length of roughness. The effectiveness of rough wall can also be found in the power spectra of streamwise component. The energy containing region agrees to both undisturbed and disturbed flow but shifting in power spectra appears which primarily depends on strength of disturbances.