**5.2 Effects of the total temperature and swirl distortion on the aerodynamic stability of fans**

The stability margin loss of the rotor increases under the total temperature and swirl distortion when the total temperature distortion decreases or the swirl distortion increases (see **Figure 15**). The binary linear regression is performed on the numerical simulation results, and the regression coefficient is about 93.0%.

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The instability mechanism under the total temperature and swirl distortion is generally similar to that under the total pressure and swirl distortion. **Figure 16** shows unwrapped blade-to-blade snapshots of the total pressure and velocity under the maximum stability margin loss at different spans. The blockage phenomenon has spread from the cascades to the front of the cascades at 99% of the span, and a protruding low-pressure region covering the entire circumference has been formed in front of the cascade. Almost all cascades have serious stall phenomena. Although the rotor is still blocked, the influence degree and range of the blockage are weaker at 80%

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

#### **Figure 16.**

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

of the span than those at 99% of the span. The low-pressure region in front of the cascade has been reduced to two stall cells, one is big and the other is small.

Flow tends to be normal in the lower blade-height plane, but some cascades still stall. Flow tends to be normal at the span closer to the hub, but some cascades still stall. Therefore, when the rotor is under the total temperature and swirl distortion, stall and blockage appear at the tip first and then gradually spread to the midspan and root of the hub.
