The effects on fan noise of inlet steady flow distortion

The Pan Test Rig Tests on a model aero-engine fan are used to determine the effects of steady intake flow distortion on fan tone noise. Three different experimental intakes are tested; a "clean" axisymmetric intake generating little flow distortion onto the fan; a "simple" droop generating a single-lobed sinusoidal flow distortion; and a "complex" droop generating a complex multi-lobed sinusoidal flow distortion. Both far-field noise and in-duct acoustic modes are measured showing the magnitude and character of the noise due to the intake flow distortions. A theoretical prediction method is then described which is shown to give reasonable estimates of these measured effects.