Bodies with reduced surface drag

Claim 1

An annular nacelle adapted to surround a gas turbine engine, said nacelle having an inner surface and an external surface, said external surface including an upstream portion and a downstream portion adapted to receive an unbounded flow of fluid thereover in the downstream direction, said inner and outer surface extending downstream and forming a thin trailing edge of said nacelle, said trailing edge defining an outlet of said nacelle of cross-sectional area C, a plurality of alternating, adjoining, smoothly undulating generally U-shaped ridges and troughs formed in said downstream portion of said external surface, said ridges and troughs extending downstream from said upstream surface portion to said trailing edge, wherein said trailing edge is wave-shaped, said troughs in said external surface defining corresponding ridges in said inner surface and said ridges of said external surface defining corresponding troughs in said inner surface, and wherein said troughs and ridges are sized and contoured such that under a selected operating condition no significant streamwise two-dimensional boundary layer separation occurs on said external surface over the length of said troughs and ridges, wherein a prior art non-undulating smooth convexly curved surface blending smoothly with said upstream portion external surface, extending to said trailing edge and having the same cross-sectional outlet area C would have streamwise boundary layer separation over said downstream portion of said external surface during said selected operating condition.