US Patent 8943796 Variable cycle turbine engine

A gas turbine engine comprises a high spool, a low spool and an intermediate spool. The high spool comprises a high pressure turbine coupled to a high pressure compressor. The intermediate spool comprises an intermediate pressure turbine coupled to a ducted fan. The low spool comprises a low pressure turbine coupled to an open-rotor propeller. A variable area turbine section positioned between the intermediate pressure turbine and the low pressure turbine variable turbine section is configured to vary an expansion ratio across the intermediate pressure turbine to control rotational speeds of the low spool and the intermediate spool.