Patent ID: 8647054

Claim:
An axial turbomachine including a rotor blade cascade, comprising: a plurality of rotor blades each having a leading edge and a radially outer, freestanding blade tip; and an annulus wall, encasing the rotor blade cascade, with an annulus inner side by which the annulus wall is arranged directly adjacently to the blade tips, forming a radial gap between the contours of the blade tips and the annulus inner side, wherein inside an axial section of the annulus inner side lying opposite the blade tip, the annulus wall, on the annulus inner side, has at least one encompassing first radial recess, with a first and a second curvature section, which along a principal throughflow direction of the axial turbomachine is arranged at a constant radial distance from the contours of the blade tips which correspond to the annulus inner side, wherein in the principal throughflow direction of the axial turbomachine the progression on the annulus inner side has at least a third curvature section adjoining the second curvature section and a fourth curvature section adjoining the third curvature section, wherein the first curvature section is delimited from the second curvature section by a first inflection point, wherein the second curvature section is delimited from the third curvature section by a second inflection point, wherein the third curvature section is delimited from the fourth curvature section by a third inflection point, and wherein the curvatures of adjacent curvature sections have different signs.