A TOOLBOX FOR THE PRELIMINARY AERODYNAMIC DESIGN OF HIGHLY LOADED ANNULAR S-SHAPED TRANSITION DUCTS

The drive towards net-zero carbon emissions is favoring lighter, more compact compressors. For the connecting S-shaped ducts, a larger radial offset must be accommodated within the shortest length ensuring no boundary layer separation and minimum losses. The duct aerodynamic design is however significantly affected by highly complex flow field interactions requiring relatively advanced and time-consuming Computational Fluid Dynamics (CFD) simulations. To limit their use at a preliminary design stage, the Agile TooL for Aerodynamic ductS (ATLAS) is currently being developed for the industrial partner. After shaping a baseline annulus, affine transformations can be carried out to change its bulk dimensions and, for example, enforce a desirable dimensionless curvature distribution. The design space can thus be mapped with ducts sharing similar geometric properties. Candidate designs can next be identified by fast exploration via Ordinary Kriging interpolations of minimum axial length and stagnation pressure loss in a CFD database. An even sample mapping by Delaunay triangulations is used to promote a high-quality semivariance model. In the vast area ratio vs hub radius ratio space investigated here, cross-validation showed that the minimum axial length is predicted with an averaged error of 2.2% at separation and 2.1% at the recommended margin from detachment while stagnation pressure loss is approximated with a mean discrepancy of 4.8% and 2.6% respectively. These capabilities are sufficiently accurate to inform a compressor toolbox about the duct performance and therefore enable a holistic preliminary design.