## 3 Results and Discussion
### Influence on Unsteady Wake Transport in AITD
Figure 10 shows the time-averaged streamwise vorticity contour at different streamwise sections of the AITD under the different sweeping wake conditions. Comparing the wake shapes of different sections shows that the inclination of the wake increased continuously with its diffusion in the AITD. This increase occurred because the tangential velocity at the hub and shroud did not decrease proportionally with the rise of the AITD's passage, where it decreased more at the shroud than at the hub. This tangential velocity difference also led to the circumferential stretching of the wake vortices, especially in the middle and lower regions of the AITD passage, as shown by the significantly stretched vortices (marked as \"Str V\") in Sections B3-B5 in Figure 10. This stretching effect was conducive to promoting the mixing and dissipation of the wake vortices, resulting in the streamwise vorticity in the corresponding regions of Sections B3-B5 in Figure 10 being significantly smaller than that in its upper half region. Meanwhile, the stretching shape and dissipation rate of the wake vortices in this region were not consistent in the cases with different \(d/s\), which indicated that these processes were also affected by the factors related to the wake intensity. Based on the analysis conclusion of Figure 9, the AITD passage between Sections B1 and B6 was always subject to a radial pressure gradient from the hub to the shroud, which could drive the low momentum fluid from the hub to the shroud along the wake. In the lower half region of the AITD passage, this radial secondary flow drove the wake vortices to move upward, coupling with the abovementioned clockwise circumferential stretching effect, resulting in the wake vortices showing an obvious stretching phenomenon, as shown by \"Str V\" in Sections B3-B5 in Figure 10. This radial pressure gradient in the AITD passage decreased with increasing \(d/s\), which suggested that the radial pressure gradient was larger and the radial secondary flow was more significant under the condition of a small \(d/s\) (e.g., \(d/s=0.078\)). Therefore, compared with the condition of a large \(d/s\) (e.g., \(d/s=0.122\)), the wake vortex shown by \"Str V\" in Figure 10 was longer, and its dissipation was also faster under the corresponding condition of a small \(d/s\) (e.g., \(d/s=0.078\)). In Figure 10, the wake had no obvious vortex core in Section B5 when \(d/s=0.078\), while a relatively clear vortex core remained in this section when \(d/s=0.122\). The wake vortices in the upper half region moved upward and gradually converged because of the radial upward secondary flow, as shown by 'Con V' in Figure 10. This phenomenon was even conducive to accelerating the dissipation of wake vortices, especially in the case of a small \(d/s\): (1) When \(d/s=0.078\), the wake vortices (as shown by 'Con V') had gathered together in Section B2, began to squeeze and merge in Section B3, and were almost exhausted in Section B5; (2) in the case of \(d/s=0.122\), the wake vortices did not converge until Section B3, the squeezing and merging occurred in Section B4, and an obvious vortex structure remained in the upper region of Section B5. For a large \(d/s\), the decrease in the radial pressure gradient weakened the radial secondary flow and delayed the dissipation process of the wake vortices, resulting in an obvious wake vortex structure at the inlet of the LPT nozzle (Section B6), which provided an opportunity to use the sweeping wake of HPT to suppress the flow separation on the suction surface of LPT-GV. Figure 11 shows the radial distribution of the pitchwise mass-averaged total pressure coefficient and its contour in Section B6. For a small \(d/s\), the strong radial secondary flow led to the accumulation of low-energy fluid masses (such as wake vortices) near the shroud.