## 3 Results
### Typical Flow Structures in the Stator Hub Corner
When stator hub clearances (not too small) exist, on the one hand, the introduced leakage flow has opposite flow direction to the transverse secondary flow near the hub, which can blow away the low energy flow that accumulated at the suction/hub corner; on the other hand, the hub corner is surrounded by the leakage flow and the main flow, both of which have relatively high streamwise velocity, so the transportation of the secondary low energy flow that rolls into the recirculation region around focus point F was suppressed; as a result, the hub corner stall was eliminated or delayed. In addition, it is worth noting that the flow structure at  
the five-hole probe at Plane 3 (as shown in Figure 2); and the stator static pressure rise is calculated by the pressure at Plane 3 and the pressure at Plane 4. For the stage static pressure rise coefficient, it can be seen that the distribution shown here is similar to the results in Figure 3, but with a smaller value at all conditions. This is mainly due to the difference in the data-acquired location of the static pressure rise coefficient, i.e., the results shown in Figure 3 are calculated by the compressor inlet static pressure and the pressure at plane 5 (as shown in Figure 2) which is far away from plane 4. From plane 4 to plane 5, the blade wake and the corner separating flow mix with the main flow, which results in a static pressure rise to some extent. For the stator static pressure rise coefficient, the variation of the value along with the stator hub clearance is very small at the DE condition, then becomes bigger at the PP condition, and finally becomes extremely large at the NS condition. For the rotor static pressure rise coefficient, the variation of the value along with the stator hub clearance is very small at the DE and the PP condition and then becomes a little obvious at the NS condition. Besides, at the NS condition the tendency of the variation of the rotor static pressure rise coefficient along with the stator hub clearance is almost opposite to that of the variation of the stator static pressure rise coefficient, but the amplitude of the variation of the rotor static pressure rise coefficient is much smaller than that of the stator static pressure rise coefficient. Hence, as a result, at all conditions the tendency of the variation of the stage static pressure rise coefficient along with the stator hub clearance is the same as that of the stator static pressure rise coefficient, which means that the variation of the compressor static pressure rise when stator hub clearance changes is mainly due to the variation of the flow inside the stator passage. From above, when the stator hub clearance varies, the rotor static pressure rise almost does not change, which means that the stator hub clearance has little effect on the operating condition of the rotor. The stator total pressure loss coefficient obtained from the five-hole probe results is shown in Figure 13. At the DE condition, the stator with no stator hub clearance has the lowest loss; when a small stator hub clearance (0.25\(\uptau\)) is introduced, the loss increases to some extent; when the stator hub clearance increases to 0.50\(\uptau\), the stator loss drops slightly; and when the stator hub clearance  
Figure 12: The static pressure rise coefficients of the compressor stage, the rotor, and the stator measured by using the five-hole probe. continually increases to 1.00\(\uptau\), the stator loss grows up again; this coincides well with the tendency of the variation of the compressor efficiency along with the stator hub clearances (as shown in Figure 3). At the PP condition, the stator with a stator hub clearance 0.50\(\uptau\) gets the lowest loss, and the loss at the other three stator hub clearance cases is almost the same, which agrees well with the tendency of the variation of the compressor efficiency, too.