Fluid flow machine and related method

A method of assembling a fluid flow machine comprising a first rotor and a stator positionable alongside the first rotor, each of the first rotor and the stator comprising a plurality of circumferentially distributed turbomachine blades,

• wherein the stator comprises a stator shroud structure comprising a stator shroud surface and the first rotor comprises a first rotor shroud structure comprising a first rotor shroud surface, the stator shroud surface and first rotor shroud surface together at least partially defining a radially inner flow surface of the fluid flow machine,
• wherein the first rotor shroud structure defines a first cavity, the first cavity being disposed radially inward of the first rotor shroud surface, and
• wherein the stator shroud structure comprises a first protrusion, the first protrusion being disposed radially inward of the radially inner flow surface,
• the method comprising positioning the stator such that the first protrusion extends in a direction with an axial component and into the first cavity of the first rotor shroud structure.