US Patent 8646721 Fluid dynamic device with thrust control shroud

A fluid dynamic device (100) for directing fluid flow to generate thrust comprising a thrust control shroud (130) disposed about a central axis (210) of said fluid dynamic device (100) for directing a fluid flow between an upstream fluid intake region (220) and a downstream fluid exit region (222), forming a fluid exit area, of said shroud (130) to generate thrust wherein a displacement of said fluid exit region (222) of said shroud (130) with respect to said central axis (210) results in a translation of said fluid exit area (222) such that the level of shear stress induced in that part of the shroud (130) disposed laterally to the direction of translation of the shroud (130) is minimized.