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. <EOS>