Turbulent boundary layers developing over rough surfaces: From the laboratory to full-scale systems

An overview of recent work on the problem of turbulent boundary layers developing over surface roughness will be given. This includes experimental laboratory studies, numerical simulations and recent attempts at full-scale in-situ measurements on the hull of an operating ship. The overarching aim here is to be able to make full-scale predictions of the penalty (economic / environmental / performance) resulting from surface roughness on the hulls of operating ships. This roughness could be due to the build-up of marine organisms on the hull of the ship or due to the surface finish attained during the hull coating process. For a given surface topography of interest, a key element to making these full-scale predictions is the ability to determine the equivalent roughness height (which is a measure of the degree to which the surface topography affects the flow). Several methods of estimating this roughness height will be discussed as well as a methodology for using this to obtain full scale predictions. Finally, a direct method will be presented for inferring the roughness penalty from an in-situ measurement of the boundary layer over the hull of an operating ship. .