US Patent 7137245 High area-ratio inter-turbine duct with inlet blowing

A bypass channel for use in an inter-turbine transition duct of a gas turbine engine is connected to a suction port disposed upstream of a high-pressure turbine and an injection port disposed downstream of the high-pressure turbine. The flow through the bypass channel is motivated by the natural pressure difference across the high-pressure turbine. The flow out of the injection nozzle is used to energize the boundary layer flow downstream of the high-pressure turbine in order to allow for the use of a more aggressively expanded inter-turbine duct without boundary layer separation.