## 3 Results and Discussion  
Figure 4(a),b show the performance of the mass flow-total pressure ratio and the performance of the mass flow-adiabatic efficiency, respectively. It can be seen that when the leakage flow rate increases, both the total to total pressure ratio and efficiency of the compressor decrease significantly. Figure 4: Grid independence. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Configuration** & **1** & **2** & **3** & **4** \\ \hline c/mm & 0 & 0.5 & 0.75 & 1.0 \\ c/h x 100 & 0 & 0.37 & 0.56 & 0.74 \\ LF x 100 & 0 & 0.11 & 0.16 & 0.20 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The clearance values and corresponding leakage flow rate for the different configurations. A comparison of compressor performance parameters at the near design point (55 kg/s) is made between the case without or with seal cavity leakage flow, which is shown in Table 4. It can be seen that when compared with no leakage, the pressure ratio is reduced by 2% and the efficiency is reduced by 1.9% for a 0.74% increase of the seal-tooth clearance-to-span ratio. The flow field comparison of the near design point with no leakage or 0.20% LF in the table is shown in Figures 6 and 7, which include the streamline traces and the absolute Mach number distribution. It can be seen from Figure 6 that the leakage flow enters the labyrinth structure of the cavity below the hub from the axial clearance behind the stator trailing edge, in which a vortex is formed many times. Then the leakage flow enters the mainstream from the axial clearance in front of the stator leading edge and mixes with it, forming a vortex at the stator root extending to the trailing edge of the stator. Due to the \begin{table}
\begin{tabular}{c c c c c} \hline  & **No Leakage** & **Clearance c = 0.5 mm** & **Clearance c = 0.75 mm** & **Clearance c = 1 mm** \\ \hline c/h \(\times\) 100 & 0 & 0.37 & 0.56 & 0.74 \\ LF = \(m_{LF}/m_{IN}\) & 0 & 0.11\% & 0.16\% & 0.20\% \\ Pressure ratio & 1.7905 & 1.7850 & 1.7579 & 1.7549 \\ Efficiency & 0.8161 & 0.8128 & 0.8014 & 0.7974 \\ \hline \end{tabular}
\end{table} 
Table 4: The comparison of compressor performance parameters at near design point. Figure 5: The performance of the compressor. existence of the whirlpool at the stator root, the mainstream migrates to the mid-span to a certain extent. As shown in Figure 7, the flow velocity at the stator root is very low. Combined with the previous Figure 6, it can be seen that the mixing of the leakage flow and the mainstream reduces the flow capacity in the stator root passage and destroys the flow field structure. Figure 6: Streamline traces. The corresponding circumferentially averaged profiles of the total pressure recovery coefficient of the stator are illustrated in Figure 8. In Figure 8, the total pressure recovery factor of the stator without leakage flow has a depression in the 7% elevation range near the root. The increase in leakage flow further enlarges the depression. As the leakage flow rate increases from 0.11% to 0.20%, the penalty of the total pressure recovery coefficient of stator root increases from 0.1 to 0.2, and the depression increases from 10% to nearly 30% in the spanwise direction, indicating that the seal cavity leakage flow has a certain destructive impact on the performance of the stator. The reasons may be as follows: on the one hand, the total pressure loss occurs when part of the fluid flows from the stator exit to the stator inlet through the cavity and the labyrinth seal under the hub, which makes the total pressure loss at the stator root higher relative to that without leakage flow; on the other hand, since the mixing of the low-energy inlet leakage with the mainstream at the leading edge of the stator, incidence changes as well as the axial momentum decreases (reflecting flow blockage), which in turn destroys the flow structure at the stator root and further increases its loss. It should be noticed that the decrease in axial momentum reflects the blockage of flow.