PIV measurements of a wake from a rough flat plate

The structure of the wake behind a submersed body greatly affects the performance and design of many engineering applications. The behaviour of the wake partially dictates the drag experienced by the body, therefore optimisation of this wake behaviour can have a significant effect on the energy required to move the body relative to the fluid. The formation of wakes over smooth bodies is well understood, however, the implications of surface roughness on the near wake structure are not well known. Surface roughness is known to greatly affect the behaviour of a turbulent boundary layer and the nature of the structures within. The subsequent interaction of these modified boundary layers in the wake modifies the formation of the wake. Roughness can be introduced into a system in a range of ways, such as manufacturing processes, surface finishes and degradation and accumulation of fouling. Therefore, the prevalence of roughness in combination with the importance of wake behaviour on performance is the motivation for the investigation of the implications of surface roughness on plane wake flows. To investigate these implications a series of 2-component - 2-dimensional particle image velocimetry (2C-2D PIV) measurements were performed on a smooth and rough flat plate in the LTRAC large horizontal water tunnel facility. The boundary layer was tripped at the leading edge and measurements were acquired in the near wake of the blunt trailing edge of the plate. The surface was roughened using commercially available sandpaper adhered to the plate surface.