Apparatus and method for cooling Axi-Centrifugal impeller

In an axi-centrifugal gas turbine engine having a plurality of axial compressor stages for compressing a main air stream followed by a centrifugal stage the centrifugal stage using an impeller to redirect the air stream, the impeller being connected at its aft end to a turbine shaft and having a plurality of forward-facing blades, a rim, and an aft face having a generally flat portion and a curved portion located radially inward from the flat portion, an improved impeller, comprising:

• (a) a curvic coupling joint between the aft end of the impeller and the turbine shaft;
• (b) a generally annular disk-shaped shield plate with an outer rim and an inner rim, the shield plate being attached near its outer rim to the impeller near its rim, the shield plate being offset from and generally parallel to the flat portion of the aft face of the impeller, thereby forming a cavity therebetween, the shield plate having a plurality of circumferentially spaced apertures near its inner rim and a plurality of radial vanes extending forward from the shield plate to the flat portion of the aft face of the impeller, the radial vanes being arranged in pairs straddling each aperture, each pair of vanes being joined together at their inner ends by a joining portion to form a U-shape, the joining portion partially surrounding the aperture, the radial vanes having outer ends that terminate radially inward from the rim to allow cooling air to flow around the outer ends;
• (c) a plenum ring extending from an area near the inner rim of the shield plate to the turbine shaft near the curvic coupling, thereby forming a cavity between the plenum ring and the curved portion of the aft face of the impeller, the plenum ring having an outer portion radially overlapping a portion of the shield plate near the inner rim of the shield plate, the outer portion having apertures aligned with the apertures in the shield plate, the plenum ring having an inner rim with an aft surface which mates with a piloting ring disposed circumferentially on the turbine shaft and located just aft of the curvic coupling, the plenum ring having radial vanes extending forward and inward;
• whereby cooling air can be directed through the apertures, into the cavity between the shield plate and the aft face of the impeller, radially outward along the vanes on the shield plate then around the ends of the vanes and radially inward to the cavity between the plenum ring and the aft face of the impeller, then inward through the curvic coupling.

A method of cooling an impeller for the main air stream of an axi-centrifugal compressor of a gas turbine engine, comprising the steps of:

• extracting a portion of the main air stream as cooling air;
• routing the cooling air through a heat exchanger;
• injecting at least part of the cooling air into a cavity between an aft face of the impeller and a shield structure attached to the aft face of the impeller;
• and
• circulating the cooling air through the cavity to cool the impeller.