Last modified: 2017-07-07
Abstract
In the present study, the wake field of a ship model was measured using a Stereo towed under water particle image velocimetry (PIV) system to identify the flow characteristics around a hull with a high block coefficient. Meanwhile, a numerical model is established based on computational fluid dynamics to provide expansion information for the experimental measurement. Detached Eddy Simulation (DES) method is employed to track the main features in the wake field. The bare hull wake was measured for a 76000 DWT Panamax Bulker model, at different Froude number of 0.056, 0.100, 0.145 and 0.167 based on the length between perpendiculars (LPP).
The measurement results show that the 76000 DWT Panamax Bulker has a similar U shaped stern as in a large vessel, such as the KVLCC, and incoming flows through the U shaped stern gradually produce a strong stern bilge vortex. The axial velocity of the propeller plan has a "hook-shaped" velocity contour at the rotating bilge vortex. In addition, under the bilge vortex, there is a propeller boss cap vortex in the opposite direction of rotation of the bilge vortex, which is close to the longitudinal section in the center disc of the ship. The presence of the hook-like bilge vortex and the counter-rotating boss cap vortex has a positive effect on improving the rotation efficiency of the propeller. The numerical results are consistent with the experimental results. By the analysis of three-dimensional flow fields, the same velocity contours (U shaped and hook-shaped) and similar vortex structures are observed. The numerical calculation has advantages in performing the spatial evolution of the complex wake vortex structure. The combination of numerical calculation method and the experimental method could enrich the wake field study for large vessels, and make the results more reliable.