Influence of hub cap shape on axial fan rotor root flow separation: An analytical model for quick design Available to Purchase

This article is devoted to elaborating the influence mechanism of hub cap shape on the rotor root flow field of axial fan and developing an analytical model for quick design of hub cap. The hub cap of various length ratio and shape was generated using a tested polynomial for an axial fan with H_r = 0.45, and numerical simulations are used to determine the variation of hub cap on axial fan flow field and aero performance. Research found that there exists a critical length ratio for hub cap such that a further reduction of the length ratio will lead to excessive meridional flow angle at the junction plane and inception of rotor root flow separation. The sharper hub cap (decrease in shape coefficient S) makes the hub separation region further expand and migrate toward the rotor pressure surface, resulting in a larger separation vortex. Furthermore, an physical-based analytical model calculating the velocity non-uniformity caused by hub cap is proposed to predict the hub cap critical length ratio for a quick design criterion of hub cap to achieve low loss while keeping short length. The analytical model calculated hub cap critical length ratio $LRCr$ for axial fan of H_r = 0.35–0.65 is 1.29–0.60 and independent of the absolute size of axial fan, which is verified by simulations.