# Optimization Design of Centrifugal Fan Blades Based on Bezier Curve Method
## 4 Result and Discussion
### Flow-Field Analysis
Regarding the pressure distribution on the suction surface, PM has a larger low-pressure region near the leading edge compared to AM, which indicates  
Figure 14: External performance characteristics of fans: (**a**) static pressure and (**b**) static pressure efficiency. Figure 15: Schematic diagram of section selection. that the optimized AM experiences a milder inlet impact flow and reduced impact loss. Overall, AM shows a more uniform pressure distribution with a reduces pressure gradient, leading to enhanced fan performance. Figure 17 shows the streamline distribution of fans. In PM, the flow separation on the blade suction side is most severe near the shroud, and the separation phenomenon decreases with reduced blade height. This is because the airflow near the shroud has not fully developed, resulting in complex local flow conditions--especially near the trailing edge, where PM exhibits significant separation. In optimized fans, with modifications to the blade curvature and outlet angle, the flow separation near the trailing edge adjacent to the shroud is improved. Additionally, in PM, a low-velocity region exists near the back plate due to the influence of the motor and the inlet incidence angle. Overall, the internal streamlines in optimized fans are smoother, with both the blade suction surface separation and the inlet impact flow being suppressed, and the low-velocity region within the impeller reduced. This indicates that the blade profile curvature optimized using the Bezier curve method better conforms to the fluid flow characteristics. Figure 16: Blade surface pressure of fans. Figure 18 illustrates the distribution of the entropy generation rate in the fan flow passage of fans based on Equations (13), (14) and (16). Overall, the regions with higher entropy generation rate are located at the blade inlet, the blade outlet, and along the blade's suction side. These high entropy generation areas are attributed to various complex internal flow phenomena, including impact losses caused by the inlet incidence angle, the jet-wake phenomena generated at the blade trailing edge, and the flow separation on the blade suction surface. In particular, the flow separation and jet-wake phenomena on the suction side near the shroud at the mid-section of the impeller are most obvious, while near the back plate, inlet impact is the dominant feature. After optimization, compared with PM, AM and BM exhibited a shift in the flow separation on the blade suction surface near the shroud toward the blade trailing edge, which suppressed the separation and reduced local entropy generation. Additionally, the entropy generation losses at the mid-section near the impeller's trailing edge were also mitigated, leading to more stable local flow conditions. Furthermore, improvements in the low-speed flow caused by the motor and the correction of the improper airflow inlet angle contributed to a reduction in the overall entropy generation rate. However, compared to PM, CM did not show significant optimization. Figure 19 shows the distribution of vortex structures captured with a \(Q\)-criterion threshold of 40,000, highlighting the close relationship between turbulence and vortices. The vortex structures were primarily concentrated in regions with unstable airflow, such as the blade inlet, blade outlet, and near the motor. After optimization, the vortex cluster and vorticity at the inlet on the blade suction surface near the back plate were reduced, and the vortex band near the back plate became significantly narrower. Additionally,  
Figure 18: Entropy generation rate of fans. the vortex cluster near the shroud at the blade outlet diminished, and the vorticity in the outlet region decreased.