Model and full scale test results relating to fan noise in-flight effects

REVIEW—A Critical Review of Turbomachinery Noise

“…Hanson [53] has pointed out that the transverse scale of distortion in the boundary layer seems too small and it must be the combination of the atmospheric distortion and the boundary layer which is important. This appears to be correct, for tests by Roundhill and Schaut [54] and Lowrie [55] with large intake screens to remove atmospheric disturbances do show great reductions in the blade passing tone. So too does removal of the annulus boundary layer at Mach numbers up to about 0.85, provided it is done sufficiently carefully to avoid increasing the level of distortion.…”

“…Every step should be made to make the inlet flow representative of the conditions prevailing when the noise is of concern. Roundhill and Schaut [54] and Lowrie [55] describe recent means of approaching this for high speed fans. It means that installations such as the large and costly ones for which the inlet flow is highly distorted should never again be contemplated.…”

Influence of a Turbulence Control Screen on the Aerodynamic and Aeroelastic Behavior of a UHBR Fan

“…In the early 1970 years it was recognized that the radiated noise of aircraft engine fans shows much higher tonal noise levels (i.e. the amplitudes of the blade passing frequency (BPF) and its higher harmonics in the acoustic spectra are higher) in static tests compared to in-flight tests [1,2,3]. This leads to the fact that flight noise levels were typically overpredicted when static test beds were used for acoustic characterization of new aircraft engines or fans.…”

“…periodic disturbances in the rotating frame of reference. This results in narrow band frequency peaks around the BPF and its higher harmonics [6,1,3]. The comparison of in-flight, windtunnel and static tests showed that these disturbances are reduced with forward speed producing BPF peaks with lowered amplitudes under flight conditions [7,8].…”

“…In order to reduce the discrepancy between static and inflight acoustic tests several research institutes started to develop so-called turbulence control screens (TCS, or inflow control device, ICD) [9,10,8,11,12]. These structures, typically consisting of honeycomb panels and/or wire-mesh screens, were placed upstream of the fan rotor in form of planar screens [3] or with a hemispherical [10,8] or geodesic shape [12] in order to ensure homogeneous inflow conditions. Acoustic and aerodynamic investigations of these structures showed a significant reduction of inflow turbulence intensities and therefore lowered BPF amplitudes and peak widths (especially at subsonic operating conditions) while broadband noise levels stayed nearly unchanged 1 Accepted manuscript, ??…”