A wind tunnel study of the mean airflow around a simple representation of a merchant ship

An investigation has been carried out to measure mean velocities above a solid block located in a wind tunnel. A Particle Image Velocimetry (PIV) system was used. The purpose of the investigation was to quantify the change in the mean flow speed caused by the bluff body and hence to determine the possible bias in wind speed measurement made from anemometers located above the superstructure of merchant ships. Possible sources of experimental error were investigated and resulted in; a) a blockage ratio correction which varied with position, b) the use of 2-dimensional maps of the free stream flow to obtain reference velocities and c) an estimate of a residual bias of up to 4 % in the PIV wind speed data. The wind speed was accelerated by up to 28 % compared to the free stream (or undistorted) wind speed. Close to the top of the block the wind speed is severely decelerated and the airflow reverses in direction. There was no dependence of either the pattern of the flow or of the magnitude of the wind speed bias on changes in wind directions of up to 30 degrees.