A propulsion system is provided. The propulsion system comprises a ducted electric bypass fan and an electrical generator powered by a turbine in an engine and configured to provide electricity to the electric bypass fan.

A maritime vehicle includes a surface for contacting a fluid medium through which the maritime vehicle is propelled. The maritime vehicle also includes an array of transducers and a controller. The transducers in the array are arranged across the maritime vehicle's surface for generating pressure waves in the fluid medium. Each transducer in the array is arranged to vibrate for generating a respective pressure wave, which propagates away from the surface in the fluid medium. The controller vibrates the transducers in the array so that the pressure waves control the drag of the maritime vehicle from the fluid medium.

Variable-porosity panel systems and associated methods. A variable-porosity panel system includes a panel assembly with an exterior layer defining a plurality of exterior layer pores and a sliding layer adjacent to the exterior layer and defining a plurality of sliding layer pores. The variable-porosity panel system additionally includes a shape memory alloy (SMA) actuator configured to translate the sliding layer relative to the exterior layer to modulate a porosity of the panel assembly. The SMA actuator includes an SMA element configured to exert an actuation force on the sliding layer and at least partially received within an SMA element receiver of the sliding layer. The SMA element extends out of the sliding layer only at a sliding layer first end. A method of operating the variable-porosity panel system includes assembling the variable-porosity panel system and/or transitioning the panel assembly of the variable-porosity panel system among the plurality of panel configurations.

Systems and methods are described herein to implement transverse momentum injection at low frequencies to directly modify large-scale eddies in a turbulent boundary layer on a surface of an object. A set of transverse momentum injection actuators may be positioned on the surface of the object to affect large-scale eddies in the turbulent boundary layer. The system may include a controller to selectively actuate the transverse momentum injection actuators with an actuation pattern to affect the large-scale eddies to modify the drag of the fluid flow on the surface. In various embodiments, the transverse momentum injection actuators may be operated at frequencies less than 10,000 Hertz.

Lifting devices are described that provide aeronautical lift by either pushing air sideways off its top surface, or by pulling away from top surface air, without changing upward air pressure on its bottom surface. In a first implementation, a pyramid shaped structure is composed of a stack of thin sections whose dimensions are rapidly extended and retracted using ultrasonic movements. Top surface air is pushed sideways when extended followed by momentary low pressure when retracted, thus providing lift. In a second implementation, a rapidly rotating lifting device is composed of a stack of thin round teethed plates, resembling circular saw blades, in which the diameter of each upper plate is slightly smaller than each lower plate. This device also creates lift as teeth push air sideways and gaps between teeth create momentary low pressure. In a third implementation, a lifting device top surface contains an array of MicroElectroMechanical Systems (MEMS) devices, such as Capacitive Micromachined Ultrasonic Transducers (CMUTs), which momentary produce lift by their upper pointing membranes rapidly pulling away from lifting device top surface air when oscillating at high frequency.

An aircraft steering system includes an electric actuator, a clutch, at least one plasma actuator, and a controller. The electric actuator is configured to vary an angle of a flight control surface of an aircraft. The clutch is configured to cut off torque by driving of the electric actuator. The torque is to be transmitted to the flight control surface. The at least one plasma actuator is configured to form a flow of air on a surface of the flight control surface when the torque is cut off. The controller is configured to control the electric actuator, the clutch, and the at least one plasma actuator.

A plasma actuator includes: a dielectric layer; a first electrode provided on the obverse surface of the dielectric layer; a second electrode provided, on the reverse-surface side of the dielectric layer, in one direction from the first electrode; a floating conductor pair that is provided between the first electrode and the second electrode and that has an obverse-surface conductor provided on the obverse surface of the dielectric layer and a reverse-surface conductor provided on the reverse-surface side of the dielectric layer, the obverse-surface conductor and the reverse-surface conductor being electrically connected to each other, electrically insulated from the first electrode and the second electrode, and positioned in the order of the reverse-surface conductor and the obverse-surface conductor in the one direction from the first electrode in plan view; and a power source connected to the first electrode and the second electrode.

A material for use in interacting with a flow is provided. The material comprises an interface surface adapted to move in response to a pressure associated with at least one wave in a flow exerted on the interface surface; and a subsurface feature extending from the interface surface, the subsurface feature comprising a phononic crystal or locally resonant metamaterial adapted to receive the at least one wave having the at least one frequency based upon the pressure from the flow via the interface surface and alter a phase of the at least one wave. The subsurface material comprises a lattice-structured material comprising a plurality of structural elements and a plurality of voids, and the interface surface is adapted to vibrate at a frequency, phase, and amplitude in response to the altered phase of the at least one wave. A method for interacting with a flow is also provided.

Structural subsurface materials and subsurface structures adapted for interacting with a flow are provided. In one example, a structural subsurface material or subsurface structure is provided for use in interacting with a fluid or solid flow. The structural subsurface material comprises a flow interface surface adapted to be disposed adjacent a flow and a subsurface feature comprising a structural material. The subsurface feature extends away from the flow interface surface. The subsurface feature alters an effective structural compliance of the flow interface surface relative to the flow such that the flow experiences an alteration in surface skin-friction drag and/or in kinetic energy in a turbulent flow. In other implementations, methods of controlling a flow with a structural subsurface material or a subsurface structure are provided. Further, methods of designing structural subsurface materials and subsurface structures for interacting with a flow are also provided.

A cavity system, comprising: a cavity (2) comprising a cavity opening; and an acoustically reflective structure (18, 20) located at least partially within the cavity (2), the acoustically reflective structure (18, 20) comprising one or more acoustically reflective surfaces (24, 26, 30, 32), each acoustically reflective surface (24, 26, 30, 32) being oblique to a plane of the cavity opening (27). The one or more acoustically reflective surfaces (24, 26, 30, 32) may be arranged to reflect incident acoustic waves out of the cavity opening while avoiding reflection into a region (48) at or proximate to a leading edge (14) of the cavity (2).