Convection to rotating disks with rough surfaces in the presence of an axial flow

The effect of surface roughness on convective heat transfer from an axial f low to a rotating disk has been measured using the transient heating techni que. A hot air flow directed at the disk was set up in a time of less than a second and local heat transfer coefficients were deduced from the tempera ture response of the disk surface, which was monitored using thermochromic liquid crystals. The surface roughness took the form of small, isolated squ are studs arranged in a square array on the disk surface; three configurati ons were investigated and the results were compared with data for a smooth disk. The studs increased heat transfer rates in turbulent boundary layers by about a factor of two and reduced the transitional Reynolds number by an order of magnitude. Nusselt numbers in turbulent boundary layers could be correlated approximately using a Reynolds number, which combined the influe nces of the axial flow and the rotational flow. (C) 2001 Published by Elsev ier Science Inc.