Upwind Distortion Due to Probe Support in Boundary-Layer Observation

Abstract

An obstacle in a boundary-layer flow creates a disturbance upwind of the obstacle, consisting of a stationary vortex extending downstream on both sides of the obstacle. This flow disturbance may interfere with observation of wind profiles or fluxes. The distance of the vortex from the obstacle is of the order of the obstacle width or height, whichever is the smaller, and for obstacles which do not possess an obvious length scale, the separation distance is of the order of the boundary-layer displacement thickness. Observation from ship-mounted booms or from oil platforms should be designed so as to avoid the upstream disturbance in the boundary layer. Illustrations and examples given are taken from wind tunnel tests of R/V Flip.