The experimental study of flight effect on fan noise. 2nd report Fan noise variations due to flight effect.

The clarification of fan noise variations due to a flight effect is important for turbofan engine noise reductions and noise estimations. Therefore, the fan noise spectrum extent and the range of fan operating condition which are affected by flight effect were studied experimentally, with a turbofan engine and an inflow control device which can simulate a flight effect on fan noise in static test conditions. The fan noise reduction due to flight effect in the fan approach condition is bigger than that in the fan take-off condition, for a fan rotor aerodynamic loading generates BPF tones near take-off condition. The biggest reduced component in fan noise spectrum is a 1st fan BPF tone, whose level is 20 dB at maximum. Higher harmonic BPF tones and a buzz saw noise are also reduced due level is 20 dB at maximum. Higher harmonic BPF tones and buzz saw noise are also reduced due to flight effect, but the reduction of broadband noise is not founded in all ranges of fan operation.