# Effects of an Inclined Blade on the Performance of a Sirocco Fan
## 3 Results and Discussion
### Qualitative and Quantitative Results
#### 3.2.1 Velocity Distribution in the Impeller Passage  
The definition of the angle \(\alpha\) and the locations of the \(z=35\) mm and \(z=75\) mm planes are shown in Figure 8.  
Figures 9 and 10 show the distribution of absolute velocity for the impeller at the \(z=35\) mm and \(z=75\) mm planes for the baseline fan and model-A, model-B, and model-C under low flow rate \(Q/Q_{n}=0.483\), respectively. In Figure 9, the velocity distribution of the baseline fan is given. The velocity distribution in the impeller passages was non-uniform along the circumference. From the velocity magnitude, the maximum velocity appeared at the circumferential position of \(\alpha=90^{\circ}\), and the velocity decreased with the increase in inclination angle in the range \(90^{\circ}<\alpha<150^{\circ}\). There was a great degree of flow separation in the lowest velocity region (as shown in the dotted line rectangle 1). Within the range of \(180^{\circ}<\alpha<270^{\circ}\), the flow separation was intensified, and vortices and recirculation appeared on the pressure surface of the blade. A distinct wake separation appeared on the suction surface trailing edge (as shown in the rectangular dotted line 2). For the region \(270^{\circ}<\alpha<360^{\circ}\), the vortices on the pressure surface of the blade gradually reduced and disappeared with the increase in inclination angle. The velocity distribution trend of the improved model was approximately the same as that of the baseline fan. Model-A shows that in the rectangular region-1, the vortices on the pressure surface decreased and flow separation occurred at the front edge of the suction surface; in the rectangular region-2, the flow separation mainly occurred at the front edge of the pressure surface, and the wake separation at the trailing edge of the suction surface decreased. Model-B shows that in region-1, the flow separation on the pressure surface disappeared, but there was still flow separation on the trailing edge of the suction surface; in region-2, the flow separation on the pressure surface of the impeller passages decreased obviously, and the wake separation on the suction surface trailing edge also disappeared. The flow separation of model-C disappeared in region-1; the flow separation disappeared in the front and middle of the pressure surface, and the flow separation occurred in the trailing edge of the pressure and suction surfaces in region-2. Compared with the impeller velocity distributions of the baseline fan, the distributions of model-A, model-B, and model-C were more uniform, which shows that the flow of the best performing model was smoother and the loss of fluid flow was reduced. As shown in Figure 10, flow separation occurred at the leading edge of the pressure surface and vortices appeared in the impeller passages for the baseline fan in region-1, and flow separation occurred at the trailing edge of the blade in region-2. Model-A reduced the flow separation in region-1, where the velocity was more uniformly distributed; in region-2, the flow separation mainly appeared in the front and  
Figure 8: Definitions of the \(xy\)-plane (\(\alpha\) is in clockwise direction) and \(z\)-plane: (a) \(xy\)-plane; (b) \(z\)-plane. middle of the suction surface. Compared with the flow separation range of the baseline fan, model-A enlarged the separation area and confined the flow, and there were vortices in the impeller passage. The velocity distribution of model-B was uniform in region-1, and the flow separation appeared on the leading edge of pressure surface, whose range was very small. In region-2, a small wake separation occurred at the trailing edge of the suction surface of the blade, which was much smaller than that of the baseline fan. The flow separation of model-C in region-1 was greatly reduced, and only a small range of flow separation occurred on the pressure surface. However, in region-2, the flow separation was deteriorated and there were vortices in the impeller passages.