Abstract
An extensive measurement campaign was carried out at the von Karman Institute for Fluid Dynamics to assess the aerodynamic performance of an ultra-low aspect ratio centripetal turbine stator. The test section consisted of 18 periodic sectors of two blade passages each, tested at transonic conditions in a blow-down facility. Particle image velocimetry (2D-PIV) measurements were performed in the trailing edge area at blade mid-height. Further downstream, 16 micro virtual 3-hole pressure probes were used to measure the aerodynamic performance at about 44% of the radial chord, downstream of the trailing edge. Results describe a highly swirling flow-field characterized by a very large tangential velocity component increasing at smaller radii. The radial component decreased instead to compensate for an opening of the test section closer to its center, therefore enhancing the tangential nature of the generated flow field. Adjacent blades showed asymmetric wakes as an effect of the particular design of the nozzle. The performance analysis exhibited very high loss coefficients (always higher than 12%) which have to be related to the extremely small aspect ratio of the cascade.
Highlights
In the last decades, the typical design targets for new aero-engine architectures always involved an increase of the efficiency and of the power output of the thermodynamic cycle by maximizing the turbine inlet temperature
The quantities are plotted with respect to the local polar coordinates; R is the radial distance from the center of the test section and θ the azimuthal shift
The quantities are plotted with respect to to the the local local polar polar coordinates; coordinates; RR is is the the radial radial distance distance from from the the center center of of the the test test section section and and θθ the the azimuthal azimuthal shift shift from leading edge edge of ofaa“covered”
Summary
The typical design targets for new aero-engine architectures always involved an increase of the efficiency and of the power output of the thermodynamic cycle by maximizing the turbine inlet temperature. A possible design which meets all these requirements consists in a centripetal turbine stator located in the core of the engine, at a smaller radius than the endwall (see Figure 1) This configuration, guarantees a high degree of compactness of the component, leading to the adoption of ultra-low aspect ratio blades. The test section is described and the measurement techniques presented and critically analyzed in terms of total pressure wakes, flow angle and loss coefficient discussed, paying a particular attention to the issues related to the challenging geometrical constraints distributions at two different radial positions in the discharge section of the cascade.
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