Experimental model studies of non-newtonian soluble coatings for drag reduction

Abstract

A soluble coating has been developed which can be applied to the surface of an underwater body, with a resulting reduction in friction drag. The coating dissolves in a predictable manner so that the body rides in a boundary layer of non-Newtonian fluid. A model test program was carried out in a simple drop-tank facility, using a small body of revolution. The distance-time relationship was accurately measured and the drag derived therefrom. Tests were made in both fresh water and sea water with very promising results, although the tests were not systematic and the location of the coating was limited to the stagnation region of the nose. Reductions in total model drag of 18% with fresh water and 16% with sea water were obtained which corresponded to reductions in model friction drag of 30 and 27%, respectively. Background T HE U. S. Navy and Merchant Marine require continual improvement in the performance of their surface ships and undersea craft in order to retain a favorable and competitive position on the international scene. Unfortunately, in past years, research in marine systems has been severely neglected, and advances in the state of the art have been very modest or nonexistent. However, specific needs have been identified and research and development recently has been stimulated to focus on the most critical problems. Programs are being pursued to increase the efficiency of propulsion systems and powerplants and to reduce wave drag and friction drag. However, for all practical considerations, because the friction drag of any marine craft increases exponentially with velocity, friction drag represents the major barrier limiting the attainment of higher speeds and major performance improvements. Development of concepts and techniques for penetration of this drag barrier represents the next major formidable challenge confronting designers of advanced marine systems.