EFFECT OF CHORD LENGTH HETEROGENEITY OF STATOR ON TONAL NOISE

The emergence of ultra high bypass ratio engines requires a shorter axial length of fan nacelle, leading to the integration of pylons and struts into Outlet Guide Vanes, which is called heterogeneous stator. Based on lifting surface method, the effect of chord length heterogeneity of stator on tonal noise is theoretically investigated. The heterogeneous stator is mutated from a homogeneous stator, in which the chord of one pair of vanes located in circumferential opposite position is gradually elongated. It was found that the unsteady loading distributions on different vanes of the heterogeneous stator deviates from the homogeneous case, with the deviation being more pronounced for the vanes adjacent to the elongated vanes. If the Tyler-Sofrin mode is cut-on in homogeneous case, a V-shaped modal distribution of sound energy can be seen for non-Tyler-Sofrin modes. As the growth of chord length heterogeneity, the non-Tyler-Sofrin modes of downward sound energy increase rapidly to the level comparable with the Tyler-Sofrin mode, while Tyler-Sofrin mode is still dominant in upward sound energy. If the Tyler-Sofrin mode is cut-off in the homogeneous case, sound energy will be regenerated and increase rapidly.