This disclosure relates to a system for reducing cavitation at a surface that moves relatively with respect to a first fluid. The system comprises a degasser configured to at least partially degas a second fluid. The system also comprises a reservoir in communication with the degasser and configured to house the at least partially degassed second fluid, the reservoir having an outlet that is arranged for directing the second fluid towards the surface. The system is configured such that the directing of the at least partially degassed second fluid towards the surface forms a boundary layer at the surface. The boundary layer is adapted to at least partially increase the negative pressure required to initiate cavitation at the surface so as to reduce the occurrence of cavitation during such relative movement.

A fluidic system is disclosed. The system comprises a plurality of fluidic oscillatory actuators, and at least one synchronization conduit connecting two or more of the actuators such as to effect synchronization between oscillations in the two or more connected actuators.

A device for reducing friction of a viscous fluid flow in a conduit is disclosed. The device comprises a body positionable to define at least a segment of a flow path for the viscous fluid in or contiguous with the conduit, a cavity in the body for retaining lubricating fluid, and at least one port in the body for delivering lubricating fluid to the cavity. A fluid outlet arrangement from said cavity delivers lubricating fluid to the flow path to form a downstream lubricating film at the conduit surface. The fluid outlet arrangement comprises a substantially continuous opening or ring of close spaced openings, effective collectively to reduce the pressure variation and therefore velocity variation of the delivered lubricating fluid along said outlet arrangement.

A propulsion system coupled to a vehicle. The system includes a diffusing structure and a conduit portion configured to introduce to the diffusing structure through a passage a primary fluid produced by the vehicle. The passage is defined by a wall, and the diffusing structure comprises a terminal end configured to provide egress from the system for the introduced primary fluid. A constricting element is disposed adjacent the wall. An actuating apparatus is coupled to the constricting element and is configured to urge the constricting element toward the wall, thereby reducing the cross-sectional area of the passage.

A flow guide body for an aircraft includes a main body having an outer aerodynamic surface having a plurality of outlet openings, and flow control devices, each having an inlet, an interaction chamber, a first outlet and a second outlet. A first control inlet is connected to the interaction chamber at the first side of the chamber axis. The outlets are each connected to outlet openings in the aerodynamic surface. Each outlet has a control outlet. A second flow control device is arranged such that one outlet is connected with the inlet of the first flow control device. One of the control outlets of the first flow control device is connected to the first control inlet of the first flow control device, and the other of the control outlets of the first flow control device is connected to the first control inlet of the second flow control device.

A combination of an airfoil, turbine blade, or compressor blade with a flow separation control device includes an airfoil, a flow separation control device, and an injection system. The airfoil includes a body with an upper surface and a lower surface that extend from a leading edge to a trailing edge. The flow separation control device includes a plurality of openings on the upper surface of the body. The injection system includes an inlet tube, a pump in gaseous communication with the inlet tube, and a flow regulator in gaseous communication with the pump and the plurality of capillary tube.

Active fluid control systems and related methods are disclosed. A disclosed example active fluid control system includes a plurality of plenums coupled together to define a fluid flow passageway, and a plurality of fluidic actuators coupled to outer surfaces of respective ones of the plenums. The fluidic actuators define actuator inlets and actuator outlets. The fluid flow passageway defined by the plenums to fluidly couple the fluidic actuators and a pressurized fluid supply source. The plenums are configured to couple to an aircraft structure supporting an aerodynamic surface to enable the actuator outlets to be mounted to the aerodynamic surface. The fluidic actuators are configured to provide the pressurized fluid to the aerodynamic surface to modify an aerodynamic characteristic of the aerodynamic surface.

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, fluid mixing, heat transfer, and/or other interactions of the fluid flow with the surface. In various embodiments, the transverse momentum injection actuators may be operated at frequencies less than 10,000 Hertz.

An aircraft control system includes a flow control device and a control circuit. The flow control device is configured to control a flow of air around an aircraft. The control circuit is configured to control the flow control device so that a pressure distribution loaded on a surface of a structure that constitutes the aircraft is equal to a control value of a pressure distribution calculated based on a physical quantity detected by a sensor provided in the aircraft. The physical quantity relates to the air.

Disclosed herein are a method and a system for forming an air layer over a portion of an engineered surface, wherein the air layer is formed with a reduced flux and preferentially steering gas away from, or toward, a specific location by way of a hydrophobic surface, a hydrophilic surface, and/or a structured surface. Moreover, disclosed are a method and a system for recovering or separating a portion of the gas or other fluid layer.