On the flow instability caused by large scale boundary-layer flow separation in highly loaded compressor/fan blade passage, a novel bifurcate compressor blade is designed based on pressure gradient control idea for blade passage flow, and a distinctive variable solidity bifurcate blade concept and three-dimensional blade design technology are integrated to achieve this design idea in this paper.

The quantitative flow information for the bifurcate blade passage is obtained by numerical simulation method to investigate the separation flow structure and dynamic mechanism near the wall and in the wake flow area. Besides, the complex influence of vortex structure evolution and the dynamic mechanism of low energy fluid redistribution being controlled in boundary-layer flow area would be revealed by applying the vorticity dynamics theory. The variable law of design parameters is explored in order to decrease aerodynamic loss, to delay flow separation near the wall and corner for the blade surface, to restructure blade aerodynamic loading, to form gentle pressure gradient and to diminish wake flow loss.

The results indicate that although extra aerodynamic loss is generated by the geometric mutation of bifurcate segment, the bifurcate blade effectively restrains the migration of high-entropy secondary flow fluid in the shroud corner area, thus substantially decreasing the loss near endwall/corner, which remarkably promotes the aerodynamic performance, particularly under the condition of positive incidence angle. Moreover, the bifurcate blade skillfully remolds the pressure gradient on the blade surface, and promotes total pressure as well as velocity for the wake area that would be beneficial for the downstream rotor blade. With the introduction of key physical concepts and flow parameters of vortex/vorticity dynamics, such as boundary vorticity flux, vorticity vector, skin-friction vector and tangential pressure gradient, the physical root source and mechanism of gentle pressure gradient formation, wake flow structure being weakened, and flow separation reduction for the endwall and corner are further revealed.

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