Abstract

Method and apparatus for reducing aerodynamic drag and enhancing lift by using ultrasound to alter the structure of boundary layers. In one embodiment, a continuous thin sheet of ultrasound is radiated transversely into the boundary layer parallel to an aerodynamic surface, such as an aircraft wing, carrying that boundary layer.To ensure that the ultrasound sheet remains under (or over) the wing, means are provided to compensate for any downstream drift of the sheet with wing flow by transmitting it in a forward direction in proportion to the Mach number of the flow. The ultrasonic sheet may be applied as periodic strips spaced at predetermined downstream intervals.In order to decrease the amount of acoustical energy required to implement the techniques of the present invention and to operate in a more efficient manner, the ultrasound transmission is modulated with audio frequencies.Means for tuning the audio frequency to match various flight conditions are provided.