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An apparatus and method for cooling an impeller for an axi-centrifugal compressor of a gas turbine engine. A curvic coupling joint is used between the aft end of the impeller and the turbine shaft. A generally annular disk-shaped shield structure is attached to the aft face of the impeller and exten

An apparatus and method for cooling an impeller for an axi-centrifugal compressor of a gas turbine engine. A curvic coupling joint is used between the aft end of the impeller and the turbine shaft. A generally annular disk-shaped shield structure is attached to the aft face of the impeller and extends from the impeller rim to the turbine shaft just aft of the curvic coupling. The shield structure is offset from the aft face of the impeller thereby forming a cavity therebetween. The shield structure has a plurality of circumferentially space apertures through which cooling air passes to first circulate through the cavity by means of radial vanes to cool the impeller, then exit through the curvic coupling joint. The cooling air is then directed afterward along the turbine shaft to be used to cool high-pressure turbine blades.

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[ What is claimed is:] [1.]1. 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 and diffuser pipes, the centrifugal stage using an impeller to redirect the air stream, the impeller being connected

[ What is claimed is:] [1.]1. 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 and diffuser pipes, 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 curvic coupling joint between the aft end of the impeller and the turbine shaft;a shield structure connected to the impeller and extending from the turbine shaft near the curvic coupling joint to the impeller rim, the shield structure being generally annular disk shaped and offset from the aft face of the impeller thereby forming a cavity between the shield structure and the aft face of the impeller, the shield structure having a plurality of apertures through which cooling air passes to first circulate through the cavity to cool the impeller, then exit through the curvic coupling joint. [24.]24. 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; andcirculating the cooling air through the cavity to cool the impeller.