# Toward the Utilization of 3D Blading in the Cantilevered Stator from Highly Loaded Compressors
## 4 Application of 3D Blading in a Cantilevered Stator
### Discussion of the Experimental Results
#### 4.2.2 Effect of 3D Blading on the Flow Field Distribution  
To obtain an overview of the flow structures in the cantilevered stator, Figure 35 presents the oil-flow results of the datum stator. The separation line (SL) is denoted by the red solid line, the attachment line (AL) is denoted by the red dotted line, the spiral node is denoted by the letter F, and the saddle point is denoted by the letter S. It can be seen that at the P1 condition, under the blowing effect of the endwall leakage flow, the corner separation at the stator hub starts from the saddle point S1 and separates into S1-F1 and S1-F3 along the radial direction; the tip region also suffers corner flow separation. The upper and lower separation areas bounded by S1 are approximately symmetrical and located close to the blade trailing edge, whereas the separation region at the blade tip is independent of the hub corner separation. With the decrease of the mass flow coefficient, the corner flow separation first enlarges its radial scale at P2 and then changes the topology at P3: the separation line S1-F1 heads upstream, pushing F1 to the endwall and incurring the corner stall. According to Figure 35, the stator hub is severely blocked at the P3 condition, represented by the large-scale low-speed zone at the outlet. Further observation of the tip flow shows that at the near-stall conditions (P3, P4), the separation region at the stator hub and the tip will gradually merge at the trailing edge, which is also demonstrated in Figure 35. Finally, under the cantilevered geometry, the occurrence of the corner stall will only induce local separation flow at SL2, which is distinctively different from the conventional shrouded stator (represented by the large-scale endwall separation and a rapid expansion of the separation zone) [37; 38; 39]. Figure 36 presents the flow field distribution at the stator outlet, where the results of both the datum stator and the 3D bladed stator are demonstrated. It can be observed that the 3D blading can effectively push the leakage flow away from the blade suction surface, yet it will incur secondary leakage at the large flow conditions (in P1 and P2, the leakage flow moves into adjacent blade channel). As a result, the flow separation at the blade trailing edge is enhanced slightly. With the decrease of mass flow rate, both the leakage flow and the transverse secondary flow will be enhanced by the increase of the circumferential pressure gradient, while the difference in their variation rate makes the leakage flow approach the blade suction surface and finally accumulate toward the hub corner of the blade surface (P3 and P4). In fact, it is only at the near-stall conditions when the 3D blading manifests its advantage: at P3 and P4, the flow separation is weakened in the middle and lower part of the stator, thereby alleviating the blockage in the middle and lower span areas. Moreover, the forward sweep at the stator tip turns out to improve the flow field in the meantime, as the wake is narrowed correspondingly. Figure 34: The radial distribution of blockage and loss under different operating coefficients: (a) blockage; (b) total pressure loss. To further reveal the mechanism of 3D blading in the corner flow in the cantilevered stator, Figure 37 presents the comparison of the secondary flow velocity vector at the stator outlet. Traces of the secondary flow (CF) and the leakage flow (LF) are depicted to demonstrate the flow structures with better clarity. Apparently, the leakage flow that travels from the blade pressure surface to the suction pressure surface could hinder the circumferential migration of the secondary flow. In the datum scheme, the CF travels through the bottom of the LF and climbs to the blade suction surface, inducing a counterclockwise vortex on its left side and a clockwise vortex on its right side. Upon the utilization of 3D blading, the strengthening of the leakage flow enhances the inhibition effect of the LF on the CF, leading to secondary leakage at the P1 and P2 conditions.