**4.2 Effect of the pure total temperature distortion on aerodynamic stability of fans**

The gaseous hydrogen burner in the inlet duct heats a 180° sector of the inlet annulus to generate the total temperature distortion of the compressor inlet. **Figure 10** shows typical circumferential profiles resulting from averaging the pressure and

**Figure 8.** *Compressor map showing the effects of the 180° circumferential pressure distortion [18].*

**Figure 9.**

*Losses in the pressure ratio of stall for the 180°-extent inlet-pressure distortion [18]. (a) At constant corrected airflow. (b) At a constant corrected speed.*

#### **Figure 10.**

*Compressor profiles with the 180° circumferential temperature distortion at 96% of the designed speed [18]. (a) Compressor inlet. (b) Compressor outlet.*

temperature on each rake. The temperature profile is more sinusoidal than the desired square wave pattern at the compressor inlet. The comparison of total temperature profiles of the compressor inlet and outlet indicates that the temperature distortion persists through the compressor with only a 29% reduction in the maximum amplitude, while the total pressure distortion is completely attenuated at the compressor outlet. Also, the peak temperature distortion rotates approximately 45° in the rotor*The Influences of Combined Distortions on Fan Performance DOI: http://dx.doi.org/10.5772/intechopen.109209*

**Figure 11.** *Effects of the 180° circumferential temperature distortion [18].*

rotating direction. There is little or no circumferential distortion of the total/static pressure associated with the temperature distortion at the compressor inlet or exit [18].

Effects on the stall line of different temperature distortions are presented on the undistorted compressor map (see **Figure 11**). *T*<sup>d</sup> is the average of the temperature measurements in the heated region; *T*ud is that in the undistorted region; *T*av is the average of *T*<sup>d</sup> and *T*ud. The increased temperature distortion decreases the stall pressure ratio, while another effect is the decrease in the corrected rotor speed for a constant mechanical speed. The constant corrected speed lines also move to lower values of corrected airflow for 92% of the corrected speed [18].

**Figure 12** shows the loss in the pressure ratio of stall evaluated at constant corrected airflow Δ(*PRS*)W under different total temperature distortions. It is nearly

#### **Figure 12.**

*Loss in the pressure ratio of stall for the 180°-extent temperature distortion [18]. (a) At constant corrected airflow. (b) At a constant corrected speed.*

linear with amplitude Δ*T/T* of the temperature distortion, while the ratio of Δ(*PRS*)W to Δ*T/T* is approximately 0.75. The loss in stall pressure ratio at constant corrected speed Δ(*PRS*)N also appears to be linear, while the ratio of Δ(*PRS*)N to Δ*T/T* is approximately 0.62 [18].
