Turbomachinery generally includes an annular flowpath for fluid with one or more rotor stages disposed therein. Each rotor stage typically includes a plurality of blades or airfoils for transferring energy between the fluid and the rotor stage.
One form of a turbomachine is a gas turbine engine which generally includes a gas generator comprising a compressor for compressing air flowing through the engine, a combustor in which fuel is mixed with the compressed air and ignited to form a high energy gas stream, and a turbine which includes a rotor for driving the compressor. In gas turbine engines, rotor stages in the compressor transfer energy from the rotor to the air. In the turbine, a rotor stage transfers energy from the gas stream to the rotor. Many engines further include a second turbine, known as a power turbine, located aft of the gas generator which extracts energy from the gas flow to drive a propulsor.
In many applications, it is desirable or necessary to transmit energy between the inner and outer regions defined by the annular flowpath. In other words, it may be necessary to transmit energy across the flowpath.
Transmission of energy across a flowpath typically occurs at non-rotating fixed struts which extend through the flowpath. For example, a power take-off from the main drive shaft of a gas turbine engine may pass through a fixed strut. In some applications, it may be desirable to transmit energy across the flowpath when a fixed strut is not available. For example, in the unducted fan engine such as disclosed in U.S. Patent Application Ser. No. 647,283 U.S. Pat. No. 4,657,484--Wakeman, which includes a counterrotating power turbine with direct drive of counterrotating unducted fan blades, energy must be transmitted across the flowpath in order to change the pitch of the blades.