An encased wind turbine has a casing, rotationally symmetrical in relation to the longitudinal axis and has the cross-section of an airfoil. The radially inner upper side delimits a flow channel. A guide element is rotationally symmetrical in relation to the longitudinal axis projects by part of its length, contrary to the direction of flow, over the casing. The propeller drives a generator, arranged in the housing, for generating electrical energy. The propeller viewed in the direction of flow, is located at least approximately at the guide-element trailing edge. Impinged on by the main flow of the wind, while a bypass flow, owing to the airfoil profile, generates a negative pressure downstream from the guide element and thus accelerates the main flow, is generated between the casing and the guide element. The propeller may be located downstream from the guide element and arranged to be adjustable in its longitudinal position.