## 4 Simulation Results
### Bird Strike Analysis
#### 4.1.2 Bird Strike Analysis Using SPH Method  
The results of bird strike analysis using SPH are presented below. The deformation plots of bird strike at different time steps and disintegration of SPH are shown in Figure 7.  
The deformation plots shown in Figure 7 represents the damage of the fan blades and their progression across different blades. The bird strike analysis using SPH also shows that maximum deformation or damage is observed on first blade which comes in contact with bird. In later blades the deformation or damage is reduced due to decrease in total and internal energy of fan and disintegration of bird. The loss of total energy is shown in Figure 8.  
Figure 6: Von Misses stress (MPa).  
Figure 7: Blade Deformation in SPH model.  
The Figure 8 shows gradual decrease in energy of fan upon strike with bird. The initial total energy of the fan is above 300 kJ and at the end of analysis the total energy of the fan is reduced to 285 kJ. However, the internal energy of the fan is increased upon impact with bird. The increase in internal energy of the fan represents that high force is experienced by fan upon strike with bird. This may lead to high vibrations and unbalance force in the system which can affect the excitation of critical modes.  
The von Misses stress generated in the fan is 1258 MPa. The von Misses stress plot is shown in Figure 9. The difference in stress values of may be due to mesh size or formulation of SPH. But the error is 0.1% which is negligible. The velocity vectors of the system are shown in Figure 10. These represents the motion of SPH particles before and after strike with fan blades.  
Figure 8: Total energy and Internal energy with time respectively.  
Figure 9: Von Misses stress (SPH).  
In order to check the reliability and validity of analyses results, the results presented for bird strike analyses are compared with the bird strike experiment. The blade was recovered from a bird strike experiment on a fan with all blades [33]. The deformed shape of the blade from experiment is compared with the simulation results. [PERSON] et al. [22] has adopted the same procedure for comparing their results with the experiment. They have compared their results by scanning the blade from experiment and superimposing the deformed blade on the deformation plot of the blade obtained from simulations. For checking the reliability of results presented above the deformation plots of blade effected with bird strike event are compared with deformation plots of studied carried by [PERSON] et al. [22]. The Figure 11 presents the plats strain plot of this study and Figure 12 presents the plastic strain plot of study carried by [PERSON] et al.  
Figure 11: Plastic Strain plot.  
Figure 10: Velocity Vectors (SPH).  
Also, the stress plot of this study is compared with stress plots from study carried out by [PERSON] et al. [22]. The von Misses stress in this study is nearly 1255 MPa whereas the stress levels in study carried out by [PERSON] et al. is 1098 MPa. This may be due to difference is rotating RPMs. In this study the rotational velocity for engine rotor is 1885 rad/s whereas, in [PERSON] et al., has taken 806 rad/s as rotational velocity in their study [22]. Figures 6 and 9 present the von Misses stress plots of this study, whereas, the von Misses Stress plots from the [PERSON] et al. study are presented in Figure 13. The superimposition of the deformed blade from the experiment on a deformed blade from the simulations by [PERSON] et al. is presented in Figure 14.  
The values of the stress and strain levels were different because of the difference in loading conditions, but the patterns in both studies were same, which suggests the reliability of the simulations performed in this study.