Wind tunnel experiments on a fully appended laminar flow submersible for oceanographic survey

Abstract

This paper reports experimental measurements of the hydrodynamics forces acting on a low drag submersible. The model was manufactured using standard, cost-effective methods without undue attention paid to the roughness or waviness of the model's surface. It was seen, using flow visualisation techniques, that the laminar boundary layer extended over 70% of the vehicle length; furthermore, no separation of the flow was seen over the remaining 30% of the body. Hydrodynamic forces were measured, and a significant reduction in drag was found compared with standard turbulent submersible shapes. The low drag performance was quite resilient to changes in incidence, showing a large drag “bucket” for angles of incidence between ± 4°. With the addition of a set of cruciform fins at the rear of the body, incorporating control surfaces, it was found that for a centre of gravity position forward of 41.3% of the body length, the vehicle would be statically stable both stick-free and stick-fixed. Finally, using a pitot tube wake rake the velocity profile of the boundary layer at the propeller location was found to be that of an attached, turbulent boundary layer closely matching a $\text{1}\text{5.35}$ power law. The importance of full interference measurement tests to allow for the support strut effects is clearly demonstrated.