validation of caa prediction of noise radi- ated from turbofan intakes

16 th International Congress on Sound and Vibration, Kraków, Poland, 5–9 July 2009
6. Conclusions
The authors draw the following conclusions from this study.
• That accurate absolute predictions of far field SPL and field shapes due to BPF tones are possible
for realistic intake geometries and flows in the absence of liners provided that the source
modal content is correctly specified.
• That the prediction of attenuated tone field shapes for lined intakes requires accurate impedance
data and the inclusion at supersonic fan tip speeds of adjustments to account for non-linear
propagation close to the fan.
7. Acknowledgements
This work is supported by Rolls-Royce plc and undertaken within the Rolls-Royce University
Technology Centre in Gas Turbine Noise at the University of Southampton (UoS). The second author
is supported also by the Engineering and Physical Sciences Research Council (EPSRC) within
the Engineering Doctorate programme at the UoS. The authors are indebted to Dr. Alan McAlpine
who provided modal decay rates for use in the FDNS calculation.
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8
Far-field SPL / dB
10 dB
Measured: Hard-walled
Measured: Lined
Predicted: Hard-walled
Predicted: Lined
Predicted: Lined, N.L. effects + 4% B.L.
0 20 40 60 80 100 120
Angle from intake axis / degrees
Figure 8. Comparisons of measured and predicted far-field sound pressure levels for hard-walled and lined
configurations showing the effect of a boundary layer and non-linear propagation on the attenuation of EO
modes at 1BPF at 90% fan speed.