Numerical Investigations on Full Blended Blade and Endwall Technique

In present state of art, compressor blades can work efficiently between the span of 20%-80%, while nearly 30% of the total loss comes from endwall region. Previous studies have shown that Blended Blade and End Wall (BBEW) which is a control technique can reduce the corner separation effectively. To further reduce the loss, enhance diffusion capability and restrain the secondary flow in the endwall region, in addition of a kind of non-axisymmetric endwall, Full-BBEW technique is put forward. Firstly, the geometric method of the Full-BBEW technique is presented on a NACA65 cascade with the unchanged axial passage area. Moreover, under the category of Full-BBEW technique, according to the different geometry characteristic, BBEW (blended blade and endwall) model, IOEW (inclining-only hub) model and Full-BBEW model are presented. Then in order to find the most effective design, numerical investigation and optimization based on the Kriging surrogate model are employed on the models. Compared with the prototype, the total pressure loss coefficient decreases by 7%-9% in optimized Full-BBEW cases and the aerodynamic blockage coefficient decreases about 23%-36%. Through analysis, the blended blade geometry creates a radial pressure gradient at the end section and push the low-energy fluid up to the mainstream. As the result, the loss decreases significantly between 5%-25% span range. Meanwhile, the intersection of boundary layer weakens because of the expanded dihedral angle. On the other hand, the inclining-only hub geometry reduces the circumferential pressure gradient and restrains the crossflow in corner. Overall, though the loss in mainstream increases slightly, Full-BBEW technique can reduce the boundary layer intersection and the crossing flow in corner so that the diffusion capability further increases and the aerodynamic performance in the endwall region improves effectively.