# Performance Prediction of Composite Marine Propeller in Non-Cavitating and Cavitating Flow
## 3 Discussion  
Changes in the pitch and rake are noticeable compared with the skew. In the case of rake, it is reduced after deformation due to the bending force upstream of the propellers. Here, the maximum displacements of models 1 and 5 are 2.93 and 2.18 mm, respectively, in the flow direction. Model 1 undergoes a greater change in the rake distribution than model 5. In the case of pitch, the deformation direction of the two models is opposite to that of the rigid propeller, as shown in Figures 8 and 9. This is obvious, especially near the tip region, and results from the different elastic bending-twisting coupling effect of orthotropic composites, which is closely related to the stacking angle. In addition, the amount of change of propeller shape parameters including pitch, rake, and skew appears to be relatively smaller in the cavitating flow than in non-cavitating. It is predicted to be due to the thrust deduction caused by the occurrence of cavitation. However, the difference is not large, so the cavitation itself does not seem to have a significant effect on the amount of deformation of the composite propellers. The development of TVC on rigid and composite propellers is shown in Figure 13. It appears that the change in cavity volume depends on the deformation of the composite propellers and is strongly affected by the pitch difference, based on the rigid propeller. In the case of model 1, the pitch increased after deformation, and the cavity volume also increased compared with that of the rigid propeller. In contrast, in the case of model 5, the cavity volume decreased as the pitch decreased after deformation. Consequently, the pitch was directly related to the angle of attack of the propeller, and it had a strong effect on the volume change of cavitation. Figure 12: Shape parameters of rigid and composite propellers in non-cavitating and cavitating flows: (**a**) pitch distribution, (**b**) rake distribution, (**c**) skew distribution. Figure 13: Development of TVC (**a**: rigid, **b**: model 1, **c**: model 5, \(\sigma=1.2\)). The contours of the vorticity magnitude and iso-surface of the Q-Criteria (\(Q=1/2\)\(|\mid\omega\mid|\)\({}^{2}-|\mid D^{\prime}\mid\)\({}^{2}\)) for composite propellers (models 1 and 5) in the cavitating flow at the same rotation speed are shown in Figure 14, where \(\omega\) and \(D^{\prime}\) are the vorticity tensor and rate-of-strain tensor, respectively. The strength of the tip vortex from the model 5 propeller was weaker than that of the model 1 propeller. The sound pressure levels of the rigid and composite propellers in the cavitating flow were compared, as shown in Figures 15 and 16. The cavity volume increases after the deformation of model 1 due to the increase in pitch, and the 1 st BPF SPL increases by 1.5 dB, as shown in Figure 15. The increase in SPL of between 1 and 4 kHz (max. 30 dB) appears to be related to the TV  
Figure 16: Sound pressure level of rigid and composite propellers (model 5) in the cavitating flow. Figure 14: Vorticity contour and iso-surface of Q-Criteria of composite propellers for: (**a**,**b**) model 1, and (**c**,**d**) model 5, respectively, in the cavitating flow. Figure 15: Sound pressure level of rigid and composite propellers (model 1) in the cavitating flow. Model 5 is designed to de-pitch after the deformation and strength of the vortical flow near the tip region, and the cavity volume is also lower than that of the rigid propeller. The 1 st BPF SPL of the model 5 propeller decreases by 4.06 dB compared with the rigid propeller, as shown in Figure 16.  
The thrust of the composite propellers before and after the deformation in the cavitating flow are shown in Figures 17 and 18. The mean thrust also increased by approximately 8.5% as the pitch increased after the deformation for model 1. In case of model 5, the de-pitch behavior had a strong effect on the volume change of cavitation while the thrust of the composite propeller remained unchanged after deformation.