Tip and Junction Vortices Generated by the Sail of a Yawed Submarine Model at Low Reynolds Numbers

Results are presented on the behavior of the tip and junction vortices generated by the sail of a SUBOFF submarine model at yaw angles from 6 deg to 17 deg for a Reynolds number of $94×103$ based on model length. The measurements were conducted in a water channel on a spanwise plane 1.3 chord lengths downstream from the trailing edge of the sail. In the vicinity of the sail hull junction, the presence of streamwise vortices in the form of horseshoe or necklace vortices locally dominates the flow. As the yaw angle is increased from 6 deg to 9 deg, the circulation of the sail tip vortex increases, and is in good accordance with predictions from finite wing theory. However, as the yaw angle is further increased, the sail boundary layer separates with an overall drop in circulation. In contrast, the circulation value for the junction vortex increases with yaw angle, and only drops slightly at the highest yaw angle.