# Effect of Impact and Bearing Parameters on Bird Strike with Aero-Engine Fan Blades
## 4 Results and Discussion
### Support Stiffness and Damping Influence  
A bird strike will produce a transient impact on the bearing, and the response of the bearing depends on the stiffnesses and damping of the bearing system, which in turn, influences the bird impact response [(22)]. It can be seen in Figure 11a,b that the stiffness has a great effect on the bearing force of the rotor. The bearing forces are 193, 139 and 47.3 kN in the cases of G, S1, and S2. It is known that when the bearing stiffness is larger, the resulting bearing force is greater, and the displacement of the shaft center is smaller. The displacements of different stiffness are 1.93, 2.78, and 4.71 mm, respectively, for the cases of G, S1, and S2. Therefore, higher stiffness leads to higher stability in the fan after impact. The damping has less effect on the bird strike, and there is not much difference between the cases of G, D1, and D2. Figure 11a,d show that the stiffness and damping of bearings do not have a substantial influence on the bird strike process and the von Misesstress distribution of the blade. The same conclusion can be drawn from the results in Table 8. The kinetic energy gain of the bird is very similar for all the cases of G, S1, S2, DI, and D2.  
Figure 10: Simulation results of different initial velocities of the bird and rotational speeds of the fan: (**a**) the contact force vs. time; (**b**) the bearing force vs. time; (**c**) the max von-Mises stress on the fan at different rotational speeds; (**d**) the von-Mises stress of different initial velocities of the bird; (**e**) bird deformations of different initial velocities of the bird and different rotational speeds of the fan.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Case** & **G** & **V1** & **V2** & **R1** & **R2** \\ \hline Initial bird kinetic energy (k) & 25.59 & 20.25 & 5.38 & 25.59 & 25.59 \\ End bird kinetic energy (kI) & 82.75 & 80.37 & 74.46 & 20.30 & 34.34 \\ Kinetic energy gain (kI) & 57.16 & 60.12 & 69.08 & \(-\)5.29 & 8.75 \\ \hline \hline \end{tabular}
\end{table}
Table 7: The change in the kinetic energy for different initial velocities of the bird and different rotational speeds of the fan.  
Figure 11: Effect of changing the stiffness and damping of the fan hub support system: (**a**) the bearing force vs. time; (**b**) displacement of the axis vs. time; (**c**) bird deformations; and (**d**) the von Mises stress.  
Therefore, it can be concluded that the blade response under bird strike is almost independent of bearing parameters. However, if the stability of the fan during the bird strike is to be improved, the bearing stiffness must be changed. The study of bearing parameters can provide a reference for bearing selection, and it can provide valuable insight into the operation of the bearings after a bird strike.  
In [PERSON] and [PERSON]'s study [22], the bearing force excited by bird impact load was taken into account. After comparing the bearing forces under approximate conditions, it was found out that the bearing forces at the fan bearing were not very significant. Therefore, to simplify the calculations, we used discrete elements for the bearings.