Frictional Drag Reduction with Air Lubricant over Super-Water-Repellent Surface

This paper proposes a new concept for the frictional drag reduction technique. The new technique makes use of a specific coating surface (Super-Water-Repellent Surface) which has a highly repellent effect and an ability to form a thin air film over it under water. When supplying a small amount of air to the specific coating surface from the outside continuously, the supplied air (secondary air) is absorbed in and joined with the primary air film and spread to form a filmy air flow along the surface. This technique reduces the frictional drag because of this phenomenon.A frictional drag test in the rectangular pipe flow and a resistance test of horizontal flat plate were carried out in order to verify the validity of this technique. As a result of these tests, it was confirmed that drag reductions of about 80% and about 55% were obtained for flow velocities of 4 m/s and 8 m/ s, respectively.