Abstract: 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).

Abstract: 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).

Abstract: A cavity system that tends to increase the thickness (28) of the shear layer (22), comprising: a cavity (2) and a plurality of rods (4), for example between two and six rods; the rods (4) are positioned in the proximity of a leading edge (14) of the cavity (2) and extending across at least a part of a width of the cavity (2) in a perpendicular or oblique angle to the actual or intended flow direction (6). One or more of the rods (4) may be positioned further along the flow direction (6) compared to one or more of the other rods (4), for example to provide a zig-zag pattern of rod positions. One or more flow alteration elements (34, 38), for example channels (34) passing through the rods (4) and/or protrusions (38) extending from the rods (4), may be provided on one or more of the rods (4).

Abstract: A cavity system that tends to increase the thickness (28) of the shear layer (22), comprising: a cavity (2) and a plate (104); the plate (104) comprising a plurality of holes (4) through it, wherein the proportion of the area of the plate (104) taken up by the holes is ?60%, for example ?75% or ?90%; the plate (104) being positioned in the proximity of a leading edge (14) of the cavity (2); the surface of the plate (104) at a perpendicular or oblique angle to the actual or intended flow direction (6). The plate (104) may be positioned at an oblique angle to the flow direction (6). One or more flow alteration elements, for example elongate members (34) positioned across the holes and/or members (38) positioned directly behind or in front of the holes (4).

Abstract: A cavity system that tends to increase the thickness (28) of the shear layer (22), comprising: a cavity (2) and a plurality of rods (4) extending away from the cavity base (3) to a height extending beyond the leading edge (14); the rods (4) being positioned downstream of and in the proximity of the leading edge (14). The rods (4) may extend to different heights and/or be positioned longitudinally offset (e.g. in a zig-zag pattern). The rods may be reversibly movable to a configuration in which they are fully enclosed in the cavity (2) when the cavity (2) is closed. Flow alteration elements (34, 38), for example channels (34) passing through the rods (4) and/or protrusions (38) extending from the rod (4) may be provided on the rods (4).

Abstract: A cavity system that tends to increase the thickness (28) of the shear layer (22), comprising: a cavity (2) and a plate (104); the plate (104) comprising a plurality of holes (4) through it, wherein the proportion of the area of the plate (104) taken up by the holes is ?60%, for example ?75% or ?90%; the plate (104) being positioned in the proximity of a leading edge (14) of the cavity (2); the surface of the plate (104) at a perpendicular or oblique angle to the actual or intended flow direction (6). The plate (104) may be positioned at an oblique angle to the flow direction (6). One or more flow alteration elements, for example elongate members (34) positioned across the holes and/or members (38) positioned directly behind or in front of the holes (4).

Abstract: A cavity system that tends to increase the thickness (28) of the shear layer FIG. 1 (22), comprising: a cavity (2) and a plurality of rods (4), for example between two and six rods; the rods (4) are positioned in the proximity of a leading edge (14) of the cavity (2) and extending across at least a part of a width of the cavity (2) in a perpendicular or oblique angle to the actual or intended flow direction (6). One or more of the rods (4) may be positioned further along the flow direction (6) compared to one or more of the other rods (4), for example to provide a zig-zag pattern of rod positions. One or more flow alteration elements (34, 38), for example channels (34) passing through the rods (4) and/or protrusions (38) extending from the rods (4), may be provided on one or more of the rods (4).

Abstract: A cavity system that tends to increase the thickness (28) of the shear layer (22), comprising: a cavity (2) and a plurality of rods (4) extending away from the cavity base (3) to a height extending beyond the leading edge (14); the rods (4) being positioned downstream of and in the proximity of the leading edge (14). The rods (4) may extend to different heights and/or be positioned longitudinally offset (e.g. in a zig-zag pattern). The rods may be reversibly movable to a configuration in which they are fully enclosed in the cavity (2) when the cavity (2) is closed. Flow alteration elements (34, 38), for example channels (34) passing through the rods (4) and/or protrusions (38) extending from the rod (4) may be provided on the rods (4).