Search

This paper describes a coupled experimental and computational fluid dynamics (CFD) campaign conducted on a 1.5 intermediate turbine stage in the full range of operating conditions, from start-up to design point under variable expansion ratio and physical speed. The test maintains engine similitude conditions and allows direct comparison with CFD data to assess the predictions accuracy. The choice of variables to describe the speedlines is also addressed by using both measured and predicted data. A discussion on velocity ratio versus corrected speed illustrates the advantages of the former parameter the adoption of which produces constant shape curves in a very wide range of operating conditions. The comparison between measurements and predictions suggests that CFD, in conjunction with performance correlations, is a viable tool to predict speedlines in a fairly wide range of conditions, provided that geometrical and operational details are carefully matched.

The main annulus hot gas ingress into turbine wheel-spaces is still one of the most challenging problem designers face. During the decades, several experimental test benches were developed worldwide to improve the knowledge associated to the rim seal flow physics. Even if in some cases quite complex and advanced rig configurations were proposed, limitations in the operating conditions and in the reproduction of the real engine geometries/characteristics into the rig are present. In this paper, validated CFD computations are used to explore the impact of some experimental rigs design choices/limitations on the sealing effectiveness prediction and their ability to mimic the real engine configuration behaviour. Attention is paid on several test rig related aspects such as operating conditions, flow path configuration (blade and vane count) and accuracy in the real engine rim seal geometry reconstruction applied to the rig. From the computations it emerges that a scaled geometry operated at lab conditions is able to mimic pretty well the real engine sealing performance when rig and engine experience the same flow path ΔCp. The ability of the rig to match the engine data is not affected by the differences in main annulus Mach number between test bench and engine. A further result that emerges from the computation regards the fact that the Φ0 - ΔCp0.5 curve is not linear, proving that the linear extrapolation of rim sealing performance from test bench to real engine when rig and engine are characterized by different ΔCp0.5 values is not of general application and an alternative approach is given. Finally, it is found that the impact of vane count on the rim sealing effectiveness is significant, making the extrapolation of data from rig to engine difficult.

The demand for gas-turbine (GT) based flexible power generation and mechanical drive is increasing due to the growing penetration of renewables and due to the need to quickly adjust production and operate at part load respectively. As efficiency operability low emissions, small footprint, availability and maintainability are of paramount importance, engine designers are leaning towards aircraft engine architectures that, with appropriate modifications mostly to the combustion system and turbine, can meet market needs. To leverage the large experience from aircraft propulsion, aero-derivative engines maintain the same architecture, with a high-speed shaft core, and a low-speed shaft driven by a multi-stage low-pressure turbine. While in aircraft engines power is adjusted by changing fuel rate and shaft speed, that go hand in hand, mechanical drive engines have more stringent needs that require changing 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). Therefore, the power turbine may deliver exit flow profiles and angles that put the turbine exhaust diffuser under severe off-design conditions, with the onset of large scale separations, large kinetic losses, and ultimately a significant drop on cycle performance. This paper describes Baker Hughes, a GE company experience in the CFD assisted design and scale-down testing of aero-derivative exhaust diffusers. The design incorporates the requirements of hot-end mechanical drive in multiple the power turbine operating conditions to determine the best compromise between peak design performance and off-design operability. The test in similitude conditions considered four relevant operating points. The inlet conditions matched with the power turbine exit profiles by the concerted action of swirl vanes and perforated plates, the design of which was heavily CFD assisted. Predictions matched measurements in terms of pressure recovery, kinetic losses, and exhaust velocity profiles. Different data post-processing and averaging were 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.