Turbine rear structure with implemented outlet guide vanes.

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... modular design of the TRS test section in the facility enables efficient customization including the possibility to modify channel geometry, any individual OGV or the entire set of OGVs. The investigated configuration of TRS was designed with a polygonal outer case, recessed engine mounts, and 12 vanes arranged as shown in Figure 1. As shown schematically, the test section was equipped with six regular vanes, three thick vanes of increased thickness, and three bump vanes, with each bump vane having a recessed shroud bump. ...

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... © 2021 by ASME; reuse license CC-BY 4.0 Figure 11 shows the flow visualizations on the pressure side of bump vane at FC=0.555. It can be noted that there is a quasitwo-dimensional separation bubble formed along the leading edge on the pressure side at FC=0.555 (marked with a red dashed line). ...

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... of normalized total pressure for the regular, thick and bump vanes at all three studied flow coefficients are presented in Figure 12. Note that the wake data is shown for about half of the sector, showing the central part containing the OGV wakes. ...

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... figure shows a side-by-side comparison of experimental and numerical data. Note the reverse direction of the horizontal axes for agreement with physical set-up in Figure 1. The OGV wakes are shown from downstream the TRS module, while the polar angle increases to positive angles in direction of turbine rotation. ...

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... to the inlet swirl-angle radial gradient, (Fig. 5), the OGV load is larger in the lower spans close to the hub. This increases diffusion and secondary flows in the hub region. The hub boundary layer migrates toward the suction side and rolls up on the vane. A similar, although smaller, secondary flow loss region is formed near the shroud (Fig. 7-10). Figure 12 shows these secondary flow loss regions close to the end-walls in the suction side areas of the vane wakes. The secondary flows and the corresponding loss regions increase with increased absolute inlet swirl angle, i.e. larger flow coefficient, as expected. In CFD this can be seen as a gradual increase of these loss-regions ...

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... similar, although smaller, secondary flow loss region is formed near the shroud (Fig. 7-10). Figure 12 shows these secondary flow loss regions close to the end-walls in the suction side areas of the vane wakes. The secondary flows and the corresponding loss regions increase with increased absolute inlet swirl angle, i.e. larger flow coefficient, as expected. ...

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... while there is a clear wake increase from FC=0.622 to FC=0.66. CFD over-predicts the secondary flows and the creation of the associated loss regions in the hub and shroud suction side corners. Overall, CFD predictions are conservative, which is favorable for a reliable design. From the experimental flow visualization shown for the bump vane (Figs. 9-10) it is evident that apart from the notable flow redistribution, the boundary layers developed in the shroud region near the bump have separated both on the vane, and on the bump itself. Hence, a strong vortical flow region with decelerated fluid is created. The analysis of the streamwise vorticity distributions in the wake, which is ...

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... less optimized vane-bump design combination in the previous configuration resulted in additional substantial losses induced in the hub region which is not observed in the current design. Figure 13 presents detailed comparisons of total pressure wakes at different spans and flow coefficients for the thick vane. ...

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... flow becomes more diffusive in the hub region for increased flow coefficient, and this translates to the enlargement of the wake width, as discussed above. Figure 14 presents comparisons of circumferentially averaged downstream total pressure coefficient for the same cases as in Figure 12. It can be noticed, that the averaged CFD profiles are generally in good agreement with experiments. ...

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... flow becomes more diffusive in the hub region for increased flow coefficient, and this translates to the enlargement of the wake width, as discussed above. Figure 14 presents comparisons of circumferentially averaged downstream total pressure coefficient for the same cases as in Figure 12. It can be noticed, that the averaged CFD profiles are generally in good agreement with experiments. ...

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... This is the region where the polygonal shroud and circular-polygonal transition regions are located. For the regular and thick vanes at flow coefficient 0.555, CFD under-predicts the losses near the shroud at 85 -95 % span and over-predicts in close proximity to the shroud. The explanation for this can be seen in the total pressure contours, (Fig. 12), where CFD results over-predict the secondary flow structures. The differences are larger for the bump vane case at FC=0.555 and overall over-prediction can be observed. In the hub region, there is also a typical overprediction of the variations related to the secondary flow structures for all nine cases. For all three vane geometries, ...

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... © 2021 by ASME; reuse license CC-BY 4.0 The performance of the current OGVs regarding de-swirling the flow from the LPT to axial flow is illustrated in Fig. 15. The figure shows the circumferentially averaged downstream profiles of outlet swirl angle for all studied cases. The aim of a good design is to have the outlet swirl angles close to zero. For the regular and thick vane, the following trends can be seen. In the vicinity to the end-walls, CFD predicts the flow turning well. In the bulk ...