# Effect of Impact and Bearing Parameters on Bird Strike with Aero-Engine Fan Blades
## 4 Results and Discussion
### The Influence of Bird Impact Orientation  
Similarly to impact location, it was discovered that bird impact orientation has a significant influence on the response of the fan blades. Table 6 lists the change in the kinetic energy of the bird when impacting from seven different orientations. The most kinetic energy is obtained for the case of O4, reaching 64.73 kJ, while the least kinetic energy is obtained for the case of O2, 49.94 kJ. When the bird strikes the fan from different orientations, the bird is cut into different sizes of blocks, which have different numbers and masses, and strikes the blades in different forms.  
Figure 9a,b demonstrates the time variations of the bird's contact force and bearing force for different impact orientations. The peak forces of cases G, O1, O2, O3, O4, O5 and O6 are 359, 449, 277, 496, 375, 387 and 263 kN. The highest peak impact forces belong to the cases of O3, O1, and O5, as in the noted cases, the bird blocks have the highest masses.  
The difference between bearing forces is not significant for different orientations. The maximum bearing forces are 193, 210, 182, 17, 215, 198, and 200 kN, respectively. The trend of variation of bearing forces with time is very similar for all the cases, and the bearing is subjected to the greatest impact in the case of O4.  
The distribution of von Mises stress of the blade at t = 2.04 ms for all cases is shown in Figure 9d. As it can be seen, the maximum stress values are greater than the yield stress of the material, which causes the blade to undergo plastic deformation. The maximum blade deformation is visible in the case of O4, which can be attributed to its stress level being the highest among all the cases. Observing the stress distribution in all the cases leads to a similar conclusion. The locations with the highest stress level are usually located at the leading edge or at the root of the blade, which can be considered as the places under the highest chance of failure.  
In summary, the bird strike responses of blades are significantly affected by the impact orientations. The fan is more susceptible in the case of O4, while the bird body is cut into large blocks, leading to the production of high impact force and harm.  
[PERSON] and [PERSON]'s simulations showed that impact orientation has a significant influence on the impact force, impact duration, and kinetic energy transfer between the bird and fan [19]. The authors stated that striking from the bottom side results in the highest peak force. This is different from our conclusion. It must be stated that the orientation which generated the maximum impact force in our study was not considered in [PERSON] and [PERSON]'s study. Nonetheless, for the orientation that was investigated in both studies, the conclusions were similar. Since more impact attitudes were considered in this study, some additional conclusions were made.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Case** & **G** & **O1** & **O2** & **O3** & **O4** & **O5** & **O6** \\ \hline Initial bird kinetic energy (kJ) & 25.59 & 25.59 & 25.59 & 25.59 & 25.59 & 25.59 \\ End bird kinetic energy (kJ) & 82.75 & 82.71 & 75.53 & 76.12 & 90.32 & 83.79 & 83.22 \\ Kinetic energy gain (kJ) & 57.16 & 57.12 & 49.94 & 50.53 & 64.73 & 58.20 & 57.63 \\ \hline \hline \end{tabular}
\end{table}
Table 6: The change in the kinetic energy of the bird for different bird impact orientations.  
Figure 9: Simulation results of different impact orientations: (**a**) contact force vs. time; (**b**) bearing force vs. time; (**c**) bird deformations at t = 2.04 ms; and (**d**) [PERSON] stress at t = 2.04 ms.