Abstract
Circumferential distortion has been a concern since the early development of aeroengines, typically leading to a decrease in stability and efficiency. This paper experimentally investigates the effect of circumferential distortion on a low-speed axial fan and evaluates the potential of foam metal casing treatment (FMCT) to improve the stall margin. Distortions with different intensities were modeled by covering variable areas with wire mesh sectors. Under different distortions, the stall margin with solid casing drops significantly from 38.6% to -7.4%, while FMCT achieves a notable improvement ranging from 14% to 20%. Unsteady measurements were conducted to analyze the pre-stall behavior and the variation in the tip blade loading. The evolution of disturbance energy is presented to discuss the effects of distortion and FMCT on fan stability. It is observed that the proportion of low-frequency disturbance energy amplifies gradually when the rotor is leaving the distorted region. As the distortion angle increases, the maximum amplitude of proportion intensifies. The comparison of the disturbance energy at near stall point between solid casing and FMCT shows that the broadband disturbance energy is suppressed by FMCT. Additionally, the enhancement of stability under inlet distortion is also attributed to the redistribution of tip blade loading.
Published Version
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