Measurement of Unsteady Wake-Velocity at Ship-Model Stern

Abstract

In order to clarify the characteristics of the unsteady wake of a ship in waves, the velocity distributions at a stern section of a ship model in forced pitching motion or in incident head wave are measured by use of a propeller-type velocimeter. It is found that the variation of the time-mean velocity in pitching motion increases near the propeller position and decreases near the bottom and the water line region. The profiles of time-mean velocity in unsteady flow are similar to those of steady boundary layers. The oscillating velocity component is found to be comparable to the unsteady Stokes' solution for an oscillating flat plat, although the theoretical values are slightly different from the measured one in case of pitching motion. The result of the measurement, however, indicates that the viscous effect of the unsteady wake velocity is restricted within the region of the steady boundary layer along the hull.