A gas turbine engine comprising: forward and aft rotors rotatable about an axis, the aft rotor comprising: a rotor hub rotatable about an axis and including a bore portion and a rim; and an arm extending axially and radially inwardly from the rim, the arm having a radially inner side, a radially outer side, and a protruding ramp on the radially outer side; a row of stator vanes axially between the forward and aft rotors, each of the stator vanes including: a platform (80;180) having a first radial side and a second radial side, and a platform axial leading end and a platform axial trailing end; and an airfoil portion extending radially outwardly from the first radial side; the gas turbine engine further comprising: a cavity extending from an inlet, between the arm and the platform (80;180) along the second side, to an outlet, the inlet being between the row of stator vanes and the aft rotor and the outlet being between the row of stator vanes and the forward rotor, wherein the axial trailing end of the platform includes a rear axial face extending from the first radial side and a radially sloped face extending from the rear axial face to the second radial side; characterised in that: the protruding ramp is angled in a direction toward the radially sloped face to direct a stream of air entering the cavity at the inlet toward the platform (80; 180). forward and aft rotors rotatable about an axis, the aft rotor comprising: a rotor hub rotatable about an axis and including a bore portion and a rim; and an arm extending axially and radially inwardly from the rim, the arm having a radially inner side, a radially outer side, and a protruding ramp on the radially outer side; a rotor hub rotatable about an axis and including a bore portion and a rim; and an arm extending axially and radially inwardly from the rim, the arm having a radially inner side, a radially outer side, and a protruding ramp on the radially outer side; a row of stator vanes axially between the forward and aft rotors, each of the stator vanes including: a platform (80;180) having a first radial side and a second radial side, and a platform axial leading end and a platform axial trailing end; and an airfoil portion extending radially outwardly from the first radial side; the gas turbine engine further comprising: a cavity extending from an inlet, between the arm and the platform (80;180) along the second side, to an outlet, the inlet being between the row of stator vanes and the aft rotor and the outlet being between the row of stator vanes and the forward rotor, wherein the axial trailing end of the platform includes a rear axial face extending from the first radial side and a radially sloped face extending from the rear axial face to the second radial side; characterised in that: the protruding ramp is angled in a direction toward the radially sloped face to direct a stream of air entering the cavity at the inlet toward the platform (80; 180). a platform (80;180) having a first radial side and a second radial side, and a platform axial leading end and a platform axial trailing end; and an airfoil portion extending radially outwardly from the first radial side; the gas turbine engine further comprising: a cavity extending from an inlet, between the arm and the platform (80;180) along the second side, to an outlet, the inlet being between the row of stator vanes and the aft rotor and the outlet being between the row of stator vanes and the forward rotor, wherein the axial trailing end of the platform includes a rear axial face extending from the first radial side and a radially sloped face extending from the rear axial face to the second radial side; characterised in that: the protruding ramp is angled in a direction toward the radially sloped face to direct a stream of air entering the cavity at the inlet toward the platform (80; 180). a cavity extending from an inlet, between the arm and the platform (80;180) along the second side, to an outlet, the inlet being between the row of stator vanes and the aft rotor and the outlet being between the row of stator vanes and the forward rotor, wherein the axial trailing end of the platform includes a rear axial face extending from the first radial side and a radially sloped face extending from the rear axial face to the second radial side; characterised in that: the protruding ramp is angled in a direction toward the radially sloped face to direct a stream of air entering the cavity at the inlet toward the platform (80; 180). the protruding ramp is angled in a direction toward the radially sloped face to direct a stream of air entering the cavity at the inlet toward the platform (80; 180).