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The growing penetration of renewables calls for power generation and mechanical drive gas turbine (GT) capable of quickly adjusting production and operate at part load. Aero-derivative engine architectures leverage the large experience from aircraft propulsion, have small footprint, high performance, availability, and maintainability. Aircraft engines adjust power with fuel rate and shaft speed that go hand in hand. Mechanical drive engines need to change the delivered power by keeping the shaft speed under control to guarantee the operation of the driven equipment (an LNG compressor or an electric generator). Hence, the power turbine exhaust may deliver velocity and angle profiles that put the discharge diffuser in severe off-design with flow separations, high kinetic losses, and cycle performance shortfall. This paper describes Baker Hughes a GE company experience in the computational fluid dynamics (CFD) assisted design and similitude scale-down testing of aero-derivative hot-end drive exhaust diffusers in multiple operating points. The diffuser inlet conditions reproduce power turbine exit profiles by using swirl vanes and perforated plates, the design of which is heavily CFD assisted. Predictions match measurements in terms of pressure recovery, kinetic losses, and exhaust velocity profiles. Different data postprocessing and averaging are considered to properly factor in the diffuser losses into the overall turbine performance.

Gas turbines engine designers are leaning towards aircraft engine architectures due to their footprint, weight, and performance advantages. Such engines need some modifications to both the combustion system, to comply with emission limits, and turbine rotational speed. Aero derivative engines maintain the same legacy aircraft engine architecture, and replace the fan and booster with higher speed compressor booster driven by a single stage intermediate turbine. A multistage free power turbine (FPT) sits on a separate shaft to drive compressors for Liquefied Natural Gas (LNG) applications or generators. The intermediate power turbine (IPT) design is important for the engine performance as it drives the booster compressor and sets the inlet boundary conditions to the downstream power turbine. This paper describes the experience of Baker Hughes, a GE company (BHGE) in the design of the intermediate turbine that sits in between a GE legacy aircraft engine core exhaust and the downstream power turbine. This paper focuses on the flow path of the TCF/intermediate turbine and the associated design, as well as on the 3D steady and unsteady CFD assisted design of the IPT stage to control secondary flows in presence of through flow curvature induced by the upstream TCF.