Treatment of a non-axisymmetric casing comprising a plenum, with controlled opening

A casing of a turbine engine compressor comprising an inner annular wall and an outer annular wall delimiting therebetween an annular cavity, the inner annular wall of the casing comprising a plurality of slots hollowed out in the thickness of the inner annular wall, the slots being arranged next to one another in a circumferential direction and each extending in an axial direction, the casing further comprising a sliding ring present in the annular cavity of said casing, the sliding ring being movable in the axial direction between an open position in which said slots in the inner annular wall of the casing open into the annular cavity and a closed position in which the sliding ring covers at least some slots, the casing additionally comprising an actuating device to move the sliding ring between the open and closed positions, wherein the sliding ring comprises cavities on the inner surface thereof opposite the outer surface of the inner annular wall, the cavities being positioned on the inner surface of the sliding ring at determined points such that the cavities coincide with the slots in the closed position.