**5.1 Effect of the total pressure and swirl distortion on the aerodynamic stability of fans**

The stability margin loss of the rotor increases under the total pressure and swirl distortion when the swirl and temperature distortion increases (see **Figure 13**). When the total pressure distortion increases under the low swirl distortion or decreases under the high swirl distortion, the stability margin loss of the rotor also increases. Binary linear regression is performed on the numerical simulation results, and the regression coefficient is about 91.0%.

The instability mechanism of the total pressure and swirl distortion can be sunnitized as follows. **Figure 14** shows the unwrapped blade-to-blade snapshots of the total pressure and velocity under the maximum stability margin loss at different spans. The speed in the distorted sector is lower than that in the clean sector at 99% of the span. The blockage phenomenon has spread from cascades to the front of cascades, and a protruding low-pressure region with a width of about 10 cascades forms in front of cascades. The cascades after the low-pressure region have obvious stall. Although the rotor is still blocked, the influence degree and range of blockage at 80% of the span are weaker than those at 99% of the span, and the low-pressure region in front of the cascade has been reduced to about 7 cascade widths.

The area of the protruding low-pressure region in front of the cascade has little change at 50% of the span, and blockage is no longer obvious. The number of stalled

#### **Figure 13.**

*Stability margin loss under the total pressure and swirl distortion. (a) Total pressure distortion parameters as the abscissa. (b) Swirl distortion parameters as the abscissa.*

#### **Figure 14.**

*Different spans with a maximum stability margin loss under the total pressure and swirl distortion (from left to right: 99, 80, 50, and 10% of the span). (a) Total pressure distribution. (b) Velocity distribution.*

cascades decreases, and the overall high-speed region appears at the cascade inlet. The protruding low-pressure region in front of the cascade is not obvious at 10% of the span, and flow in the rotor tends to be normal. Therefore, when the rotor is under the total pressure and swirl distortion, stall and blockage appear at the tip first and then gradually spread to the midspan and root of the hub.
