## 3 Results and Discussions
### Effect of Aspect Ratio  
A high aspect ratio is known to reduce secondary flow effects in the blade passage, but such blades are inclined to stall. The combined effect of aspect ratio and the slot configuration on the cascade performance is not known. In this study, the aspect ratio is set as an independent variable by changing  
Figure 7: Influence of pitch-chord ratio on limiting streamlines and the passage total pressure loss coefficient at \(i=0^{\circ}\) incidence angle: (**a**) origin, \(s/c=0.926\); (**b**) origin, \(s/c=1\); and (**c**) slot, \(s/c=1\).  
the blade height, while keeping the chord constant. In order to understand the part played by the aspect ratio with effects on the slot configuration at the root of blade, the aspect ratio is varied from the datum \(h/c=1.32\) to \(h/c=1\) and \(h/c=1.65\), with and without the effect of the slot configuration. As for the original aspect ratio cascade, the height of the slot is set 10% of the whole span, so for the aspect ratio varied to \(h/c=1\) and \(h/c=1.65\), the height of the slot compared to the span height is kept as 10%, so the heights of the slot for these two cases are 0.01515 m and 0.025 m, respectively.  
Figure 8 shows the influence of the aspect ratio on the overall performance of the cascade at positive incidence angles. For the incidence angle characteristics, just four representative incidence angles (\(i=0^{\circ}\), \(2^{\circ}\), \(3^{\circ}\), \(7^{\circ}\)) were investigated. The original cascade tends to be easier to stall with the increasing aspect ratio. The total pressure loss increases gradually as the incidence angle increases for the \(h/c=1\) case. For \(h/c=1.32\) and \(h/c=1.65\) cases, total pressure loss increases rapidly at a \(3^{\circ}\) incidence angle, which corresponds to the generation of the corner stall. For the slotted cases total pressure loss decreases with the increase of the aspect ratio. This can be explained: as blade height increases, the proportion of the corner separation in the whole flow passage decreases.  
Figure 9 shows the variation of the total pressure loss coefficient for the EXP test plane at the \(i=3^{\circ}\) incidence angle for three aspect ratios. The slot configuration for all the aspect ratio cascades worked well for the control of the corner separation. The total pressure loss decreased by 13%, 29.5%, and 31% for the aspect ratios of \(h/c=1\), \(h/c=1.32\), and \(h/c=1.65\), respectively. As the slot height increased along with the increase of the blade height, the slotted blade with \(h/c=1.65\) obtained the lowest loss at the blade trailing edge.  
Figure 8: Influence of the aspect ratio for different incidence angles on the total pressure loss coefficient with and without the slot configuration.  
Figure 9: Influence of aspect ratio on the spanwise profile of total pressure loss coefficient at the \(i=3^{\circ}\) incidence angle.  
Figures 10 and 11 shows the surface flow pattern and passage total pressure loss contour at the \(i=3^{\circ}\) incidence angle. With lower aspect ratio, the separation lines extend very close to the midspan in Figure 10a. While with the increase of the span height, flow near the endwall is uncoupled with the flow at the midspan, so a large separation near the endwall is generated and the three-dimensional separation is developed into the corner stall with a high aspect ratio. From the flow pattern of the slotted cases, jets from the slot have an impact on the high loss region on the blade suction surface side and prevented the flow drift towards the midspan and also caused an upward displacement of the limiting streamlines.  
Figure 10: Influence of aspect ratio on limiting streamlines and the passage total pressure loss coefficient at the \(i=3^{\circ}\) incidence angle: (**a**) origin, \(h/c=1\); (**b**) origin, \(h/c=1.32\); and (**c**) origin, \(h/c=1.65\).