The high pressure turbine is coupled to drive the high pressure compressor.

A diffuser connects the outlet of the high pressure turbine and the inlet of the low pressure turbine.

A first spool comprises a high pressure turbine (326) and a high pressure compressor (324).

The system also includes a bypass channel for bypassing a portion of the flow around the high pressure turbine, from upstream of the high pressure turbine to downstream of the high pressure turbine.

A turbine section includes a high pressure turbine, an intermediate turbine and a fan drive turbine.

The turbine system includes a high pressure turbine having an inlet for receiving a flow of fluid, and an outlet for passing the flow on extraction of work from the high pressure turbine.

The system further includes a low pressure turbine, having an inlet for receiving a flow of fluid from the high pressure turbine.

In a turbine engine (10), low temperature air is diverted from a low pressure section of the compressor section of the engine to cool the high pressure turbine of the engine.

The high pressure impeller (18) is provided within a cavity (32), defined by an impeller recess (34) and a cover plate (36).

The nickel-base superalloy composition may be used in single-crystal or directionally solidified superalloy articles such as high pressure turbine blades for a gas turbine engine.