The Impact of Inlet Flow Angle on Turbine Vane Frame Aerodynamic Performance

Modern aero-engines are designed for high efficiency and low weight to reduce fuel consumption and achieve reductions in CO2 emissions. According to the goals and roadmap of the “Flightpath 2050” report, the Strategic Research and Innovation Agenda (SRIA) demands a drastic reduction of emissions to balance further air traffic growth. Therefore, technologies and processes allowing for a 75 % reduction in CO2 emissions per passenger kilometer compared to the year 2000 technology standard must be available by 2050. Turbine Vane Frames (TVF) are one technology to increase the efficiency of aero-engines and can therefore help to reach this goal. Turbine Vane Frames are located in-between the high-pressure turbine (HPT) and the low-pressure turbine (LPT) of an aero-engine and have three major purposes: guiding the flow to higher radii, incorporating the function of stator guide vanes of the first stage of the LPT, and passing structural components and oil pipes through the flow channel. A TVF with aft-loaded wide-chord main vanes and splitter vanes was designed, which meets engine-representative mechanical and aerodynamic constraints. A test vehicle consisting of the TVF and a first-stage LPT rotor has been designed and is currently being tested in the subsonic test turbine facility for aerodynamic, aeroacoustic and aeroelastic investigations (STTF-AAAI) at the Graz University of Technology. In the engine, the TVF needs to function at high performance not only at the aerodynamic design point (cruise) but also at off-design conditions. A splittered TVF design features complex flow fields with strong secondary flow interactions, and because of the fundamental design differences, the flow field characteristics within a TVF are different from those in a conventional LPT vane row. This paper discusses the flow field in a splittered TVF with emphasis on secondary flow structures and their interaction with each other and the main flow. To examine the influence of different swirl angle levels on the flow field and loss generation mechanisms inside the TVF, the swirl angle upstream of the TVF is numerically changed in a wide range from positive to negative angles. The objective of this study is to examine the sensitivity of the splitter vanes to large flow angle deviations, as present in part-load operation. Additionally, the flow field downstream of the TVF and its influence on the LPT rotor performance is described in detail. The size and locations of separated flow regions resulting from the off-design incidence of the flow and their impact on the rotor are investigated and quantified. A loss breakdown is presented to discuss the impact of incidence variations on the performance of both the TVF and the LPT.