Experimental study of the velocity field induced by a propeller jet in an inland-ship model and the related bed scour

The highly turbulent flow induced by ship propellers has a great potential to scour the alluvial bottom of navigational rivers and canals. Characterization of the complex flow field behind propellers is essential for forecasting the scouring action. In this study the velocity field and scour induced by two standard arrangements of propeller, nozzle and rudder from inland vessels are investigated experimentally with a ship model on a scale of 1:16. There are two objectives: first, to identify the influence of the ship stern on the flow field, and second, to assess induced scour depths in relation to maximum current velocities close to the bottom. It is found that the equilibrium scour depths for the two propeller arrangements are of the same order of magnitude, but that the time development of scour is different. The differences can be explained by the converging trend of the flow velocities at the bottom level for the two situations, when the vertical distance between the propeller and the bottom is high. It is also shown that existing relations for the velocity field require amendment when the propeller is ducted, and for adequately considering the effect of the ship stern and rudder type