The Coandă effect is the tendency of a fluid jet to stay attached to a surface of any form. Merriam-Webster describes it as "the tendency of a jet of fluid emerging from an orifice to follow an adjace
A diagram of a generic engine that harnesses the Coandă effect to generate lift (or forward motion if tilted 90° on its side). The engine is approximately bullet or inverted bowl shaped, with fluid being expelled horizontally from a circular slit near the top of the bullet. A small step at the lower edge of the slit ensures that a low pressure vortex develops immediately below the point where the fluid exits the slit (see Diagram 5). From there on the Coandă effect causes the sheet of fluid to cling to the curved outer surface of the engine. The entrainment of the ambient fluid into the stream flowing over the bullet, causes a low pressure area above the bullet (Diagrams 1–5) . This, together with the ambient ("high") pressure below the bullet causes lift, or, if mounted horizontally, forward motion in the direction of the apex of the bullet.