A turbine section for a gas turbine engine comprising: a first rotor assembly with a first rotor assembly bleed air source and a first stage aft cavity in fluid communication with the first rotor assembly bleed air source; a second rotor assembly downstream of the first rotor assembly including a second stage forward cavity; and a seal extending between the first rotor assembly and the second rotor assembly; the seal being a segmented seal and including a plurality of knife edges that mate with an abradable material on a radially inner end of a vane separating the first rotor assembly from the second rotor assembly, characterised in that: a radially inner edge of the abradable material is located between approximately 10% and 50% of a radial length of a root portion of a blade of the first rotor assembly from a radial inner edge of the root portion of the blade, the first stage aft cavity is downstream of the first rotor assembly and bounded by the first rotor assembly, the seal and the vane, and the second stage forward cavity is upstream of the second rotor assembly and bounded by the second rotor assembly, the seal and the vane; and a vane bleed air source is in fluid communication with the second stage forward cavity, wherein the first rotor assembly bleed air source is at a first pressure and the vane bleed air source is at a second pressure lower than the first pressure. a first rotor assembly with a first rotor assembly bleed air source and a first stage aft cavity in fluid communication with the first rotor assembly bleed air source; a second rotor assembly downstream of the first rotor assembly including a second stage forward cavity; and a seal extending between the first rotor assembly and the second rotor assembly; the seal being a segmented seal and including a plurality of knife edges that mate with an abradable material on a radially inner end of a vane separating the first rotor assembly from the second rotor assembly, characterised in that: a radially inner edge of the abradable material is located between approximately 10% and 50% of a radial length of a root portion of a blade of the first rotor assembly from a radial inner edge of the root portion of the blade, the first stage aft cavity is downstream of the first rotor assembly and bounded by the first rotor assembly, the seal and the vane, and the second stage forward cavity is upstream of the second rotor assembly and bounded by the second rotor assembly, the seal and the vane; and a vane bleed air source is in fluid communication with the second stage forward cavity, wherein the first rotor assembly bleed air source is at a first pressure and the vane bleed air source is at a second pressure lower than the first pressure. a radially inner edge of the abradable material is located between approximately 10% and 50% of a radial length of a root portion of a blade of the first rotor assembly from a radial inner edge of the root portion of the blade, the first stage aft cavity is downstream of the first rotor assembly and bounded by the first rotor assembly, the seal and the vane, and the second stage forward cavity is upstream of the second rotor assembly and bounded by the second rotor assembly, the seal and the vane; and a vane bleed air source is in fluid communication with the second stage forward cavity, wherein the first rotor assembly bleed air source is at a first pressure and the vane bleed air source is at a second pressure lower than the first pressure.