1. Abird impact on a fan blade i s depicted i n figure 1. The bird f i r s t strikes the leading edge pressure side of the blade and begins to flatten. The bird continues to spread across the blade and after fully impacting slides o f f the blade. Note that if the bird i s sufficiently large only part o f the bird may actually impinge upon the blade. The bird i s usually sliced by the blade and the rear portion o f the bird may pass behind the blade without hitting it. In the MMBI analysis the pressure loading on the impacted surface of the blade i s determined by modeling the bird as a composite of 2-0 and 3-D fluid jets as shown i n figure 2. As the impacting portion of the bird spreads over the blade the leading and trailing parts are modeled by a 2-0 oblique impinging fluid jet. The sides are modeled by halves o f a 3-0 circular impinging jet. As the impact progresses with time, the newly impacted portion of the bird expands as a ring while the next portion impacts on the blade. If the bird impacts completely it continues to expand as a series of concentric rings.
2. Part of the function of the pre-processor i s to create the f l a t plate representation of the blade. For cambered and twisted fan blades the two dimensional flat plate mode 1 cannot reproduce the blade planform geometry exactly. Because of the double curvature some geometric distorsion i s unavoidable. However, the effects on the calculated pressure distribution should be very small for typical fan blade designs. The only data needed to create this model i s the location of the blade stacking axis along each row of nodes i n the impact model. Procedures within the analysis package w i l l automatically form the f l a t plate model. The arc length of each row of nodes i s f i r s t calculated, then the "straightened" rows are positioned as to preserve the location of the stacking axis along each row.