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).