According to the present disclosure there is provided an arrangement for influencing liquid flow, the arrangement comprising: a first section selectively configurable to provide a vortex generator surface to induce vortices in the liquid flow. The arrangement further comprises a second section, wherein the first section and second section are movable relative to one another to provide the vortex generator surface.

According to the present disclosure there is provided an arrangement for influencing fluid flow, the arrangement comprising: a first section selectively configurable to provide a vortex generator surface, the vortex generator surface comprising a series of laterally aligned projections, to induce vortices in the liquid flow.

A foil, such as an aerofoil, having a leading edge and a trailing edge, of which at least a portion of one or both of the leading edge and trailing edge has a serrated profile comprising a plurality of adjoining teeth, each tooth having a tip point that represents a local maximum chord-wise extent of the tooth and, on each side span-wise of the tip point, a root point that represents a local minimum chord-wise extent of the tooth and at which the tooth adjoins a respective adjacent tooth, wherein the tooth edge profile varies with an ogee-like curve between tip point and root point such that the tooth is sharper in the neighbourhood of the tip point and in the neighbourhood of the root point than at locations in between.

According to the present disclosure there is provided a liquid flow influencing duct arrangement comprising: a first duct section arranged to receive a liquid flow therethrough, the first duct section defining a first direction through the first duct section from a liquid inlet end to a liquid outlet end; a second duct section defining a second direction through the second duct section from a liquid inlet end to a liquid outlet end, the second duct section comprising a vortex generator surface, wherein the vortex generator surface is arranged to induce vortices in the liquid flow through the first duct section, wherein the duct arrangement further comprises a rotor housed in one of the duct sections.

A vehicle includes a propulsion unit configured to move the vehicle and to change a characteristic of the environment of the vehicle. The vehicle also includes a proximity sensor configured to detect the characteristic of the environment of the vehicle. The characteristic of the environment is changed by operation of the propulsion unit. The vehicle further includes obstacle detection circuitry configured to determine a presence of an obstacle in the vicinity of the vehicle based on a comparison between the detected characteristic of the environment and a reference value.

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).

A foil, such as an aerofoil, having a leading edge and a trailing edge, of which at least a portion of one or both of the leading edge and trailing edge has a serrated profile comprising a plurality of adjoining teeth, each tooth having a tip point that represents a local maximum chord-wise extent of the tooth and, on each side span-wise of the tip point, a root point that represents a local minimum chord-wise extent of the tooth and at which the tooth adjoins a respective adjacent tooth, wherein the tooth edge profile varies with an ogee-like curve between tip point and root point such that the tooth is sharper in the neighbourhood of the tip point and in the neighbourhood of the root point than at locations in between.

A flow body for an aircraft includes a recess in a surface of the flow body, a first structural component with a porous material and may also include a second structural component with a porous material. The recess includes a front recess region and a rear recess region. The first structural component is arranged in, or on, the front recess region and the second structural component may be arranged in, or on, the rear recess region. An aircraft having the flow body, a weapons system having the flow body and a method for manufacturing a flow body for a vehicle are also described.