Partial Cavity Drag Reduction at High Reynolds Numbers

摘要

Air lubrication to reduce hull skin friction is an idea that originated more than a century ago. There are few implementations of this concept, and there are even fewer systematic investigations at high Reynolds numbers. To address this, an experimental investigation was performed at the W. B. Morgan Large Cavitation Channel that examined the drag-reducing effects of a ventilated partial cavity at high Reynolds numbers. The design was accomplished using both linear gravity wave theory and a two-dimensional inviscid numerical model via Fluent. The physical model was a 12 m long flat plate with a plenum on the bottom. The plenum was formed by an abrupt step near the nose and a long sloping reattachment region toward the rear. Air was injected from the aft face of the step to create a cavity approximately 17.8 cm deep. Friction loads, air flow, and cavity pressure were measured over a range of air fluxes and speeds near the cavity design speed of 3.4 m/s. Cavities were shown to be stable with respect to large changes in air flux and slow perturbations in tunnel speed and pressure. Stable cavities were produced that reduced the skin drag by more than 95% over the extent of the cavity, including the cavity closure.