Influence of Aerodynamic Probes for Measuring Distorted Inflow on the Performance in a High-Speed Axial Flow Fan

Experimental evaluation of aero-engine compressor performance under distorted inflow conditions is clearly specified in airworthiness standards. Generally, to quantify the distortion intensity, six to eight multihole comb pneumatic probes were experimentally used to capture the circumferentially distorted flow field. Although the blockage ratio of the probes meets the requirements when designing them, whether the presence of the probes will cause changes in the distorted flow after passing through the probes, then affects the accuracy and reliability of performance evaluation under distorted inflow has not been conclusively determined. To address this issue, a numerical study was conducted on the distortion intensity with and without inlet-measuring pneumatic probes in a two-stage high-speed axial flow fan of an aero-engine. The results show that, compared with the case without pneumatic probes, the installation of inlet pneumatic probes increases the inlet total pressure and temperature distortion intensities by 0.011 and 0.0015, respectively. However, the pneumatic probes can act as guide vanes to reduce the swirl angle, which leads to a significant 0.0411 decrease in the swirl distortion intensity (τ_ct). This reduction in swirl distortion further decreases the angle of attack at the rotor blade leading edge and increases the inlet axial velocity, thereby enhancing the flow capacity and improving the corrected flowrate and pressure ratio by 1.09% and 1.56%, respectively. The optimization of the inlet angle of attack reduces flow separation and increases the efficiency by 1.7%. Accounting for the influence of the probes brings the numerical simulation results closer to the experimental data. It demonstrates that the pneumatic probes exert a dual effect on the distorted flow field in practical applications, necessitating careful balancing during the design and experimental processes.