Analysis of the hull wake of a twin-screw ship in steady drift by Borescope Stereo Particle Image Velocimetry

The hull wake of a twin-screw ship in steady drift is analysed by means of a novel Stereo Particle Image Velocimetry (SPIV) system based on rigid endoscopic devices (borescope). The measurement apparatus is described in detail; advantages, drawbacks, processing methodology are presented and discussed. In particular the main advantages are: on-board measurement capability, low intrusiveness and no need to develop water-proof camera casings. Steady drift testing are carried out at CNR-INM towing tank, drift angles β=8.4∘,±13∘,±27∘. Modifications of the windward and leeward sides of the hull wake are investigated and their asymmetric features highlighted. In particular, the former is found to be perturbed to a larger extent at moderate drift angles, whereas the latter is characterized by the presence of coherent vortex structures which feature a high degree of spatial and time coherency.