## 3 Results and Discussion
### Effect of Wake on the Integrated LPT-GV
In the  
Figure 12: Distribution of the time-averaged static pressure coefficient on the integrated LPT-GV in the AITD. lower region of the LPT-GV, a passage vortex (marked by PV@H in Figure 13) was near the hub even during the sweeping wake cycle in all cases. Because of the radial secondary flow from the AITD shroud to the hub, this passage vortex hardly expanded in the radial direction downstream. For the same reason, the decrease in the radial pressure gradient also led to the weakening of this passage vortex, which could also be proven because the passage vortex at the lower part of the LPT-GV was smallest when \(d/s=0.122\). As the midspan was the most significant region of the integrated LPT-GV affected by the sweeping wakes, its boundary layer was analyzed in detail below to reveal the influence of unsteady wakes. Figure 14 shows the space-time diagram of the boundary layer shape factor (H\({}_{12}\)) and loss coefficient (\(\xi\)) at the midspan of the integrated LPT-GV when \(d/s=0.078\), 0.10 and 0.122. The leading edge/certline/trailing edge of the wake (Lines A, L and B, respectively), the boundary of the calm zone (Line C) and the transition position (Line T) induced by the wake are also shown in Figure 14 according to the empirical judgment criterion. The shape factor was the ratio of the displacement thickness of the boundary layer to its momentum thickness: the lower the shape factor was, the fuller the velocity profile of the boundary layer; in contrast, the velocity profile was concave, which often indicated that flow separation might have occurred in the boundary layer. Based on the conclusions verified by the experiment, when the shape factor was greater than 3.5, boundary layer separation of the LPT blade often occurred [34]. In all cases, the shape factor was relatively small (H\({}_{12}<3.5\)) in the wake sweeping cycle, as shown by the blue area between Line A and Line C in the space-time diagram of the shape factor, indicating that the sweeping wake could well inhibit the flow separation at the midspan of LPT-GV. With the increase in \(d/s\), the width and turbulence intensity of the sweeping wake increased, as did its influence range. When \(d/s\) increased from 0.078 to 0.122, the area between Line A and Line C, representing the influence range of the sweeping wake, increased from 0.24T to 0.5T at \(x=0.55C_{x}\) in the upper row of Figure 14. This prolongation of wake inhibition apparently helped to reduce losses due to flow separation on LPT-GVs. In the gap of the sweeping wake, the shape factor increased and exceeded 3.5 in all cases, as shown in the area circled by the isoline of H\({}_{12}=3.5\) in the upper row of Figure 14, which meant that the boundary layer separation bubble recovered again. With increasing \(d/s\), the separation  
Figure 13: Limited streamline and static pressure coefficient contour on the suction surface of the integrated LPT-GV. bubble zone delineated by the isoline of H\({}_{12}\) = 3.5 not only significantly reduced the time range (due to the increased influence range of the wake) but also continuously reduced its axial range (representing the size of the separation bubble) and peak value (representing the thickness of the separation bubble). This result was obtained for the following reason: although in the wake gap, the mixing and dissipation of the wake upstream enhanced the turbulence intensity of the main flow at the inlet of LPT-GV to a certain extent, with increasing \(d/s\), the further enhanced turbulence intensity was conducive to promoting energy exchange between the boundary layer and the main flow and induced the boundary layer transition earlier, resulting in better suppression of the size and thickness of the boundary layer separation bubble. The loss coefficient of the boundary layer represented the viscosity loss in the boundary layer.