A turbomachine, comprising: a forward stage including a forward stage rotor disk including a forward stage rotor disk rim, wherein the forward stage rotor disk is disposed radially adjacent to a shaft at a forward stage rotor disk bore; and a plurality of intermediate stages in axial sequence, which are aft of the forward stage, each intermediate stage including an intermediate stage rotor disk, wherein each intermediate stage rotor disk includes: an intermediate stage disk body; an intermediate stage disk rim configured to connect to or include a rotor blade disposed on a radially outward portion of the intermediate stage disk body; and an intermediate stage disk bore defined in a radially inward portion of the intermediate stage disk body and disposed radially adjacent to the shaft; and an aft stage, which is aft of an aftmost intermediate stage, including an aft stage rotor disk having an aft stage rotor disk bore, characterised in that: each intermediate stage rotor disk has an intermediate stage rotor disk thermal regulation aperture disposed in a radially outward half of the intermediate stage disk body towards the rim for allowing flow to pass axially through the intermediate stage disk body; and in that at least one bleed hole is included in at least one of an aft portion of the forward stage rotor disk rim or a forward portion of the foremost intermediate stage rotor disk rim to allow cool air from the forward stage to pass through the rim, through the thermal regulation apertures of the plurality of intermediate stage rotor disks, into a cavity between the aftmost intermediate stage and the aft stage and down to the aft stage rotor disk bore to regulate a temperature differential of the aftmost intermediate and/or aft stage rotor disk. a forward stage including a forward stage rotor disk including a forward stage rotor disk rim, wherein the forward stage rotor disk is disposed radially adjacent to a shaft at a forward stage rotor disk bore; and a plurality of intermediate stages in axial sequence, which are aft of the forward stage, each intermediate stage including an intermediate stage rotor disk, wherein each intermediate stage rotor disk includes: an intermediate stage disk body; an intermediate stage disk rim configured to connect to or include a rotor blade disposed on a radially outward portion of the intermediate stage disk body; and an intermediate stage disk bore defined in a radially inward portion of the intermediate stage disk body and disposed radially adjacent to the shaft; and an intermediate stage disk body; an intermediate stage disk rim configured to connect to or include a rotor blade disposed on a radially outward portion of the intermediate stage disk body; and an intermediate stage disk bore defined in a radially inward portion of the intermediate stage disk body and disposed radially adjacent to the shaft; and an aft stage, which is aft of an aftmost intermediate stage, including an aft stage rotor disk having an aft stage rotor disk bore, each intermediate stage rotor disk has an intermediate stage rotor disk thermal regulation aperture disposed in a radially outward half of the intermediate stage disk body towards the rim for allowing flow to pass axially through the intermediate stage disk body; and in that at least one bleed hole is included in at least one of an aft portion of the forward stage rotor disk rim or a forward portion of the foremost intermediate stage rotor disk rim to allow cool air from the forward stage to pass through the rim, through the thermal regulation apertures of the plurality of intermediate stage rotor disks, into a cavity between the aftmost intermediate stage and the aft stage and down to the aft stage rotor disk bore to regulate a temperature differential of the aftmost intermediate and/or aft stage rotor disk.