Type of Document Dissertation Author Hutcheson, Florence Vanel Author's Email Address email@example.com URN etd-110499-180010 Title Advanced modeling of active control of fan noise for ultra high bypass turbofan engines Degree PhD Department Mechanical Engineering Advisory Committee
Advisor Name Title Fuller, Christopher R. Committee Chair Barnwell, Richard W. Committee Member Burdisso, Ricardo A. Committee Member Dunn, Mark Committee Member O'Brien, Walter F. Jr. Committee Member Keywords
- turbofan engine
- fan noise
- active control
Date of Defense 1999-10-14 Availability unrestricted AbstractAn advanced model of active control of fan noise for ultra high bypass turbofan
engines has been developed. This model is based on a boundary integral equation method
and simulates the propagation, radiation and control of the noise generated by an engine
fan surrounded by a duct of finite length and cylindrical shape, placed in a uniform flow.
Control sources, modeled by point monopoles placed along the wall of the engine inlet or
outlet duct, inject anti-noise into the duct to destructively interfere with the sound field
generated by the fan. The duct inner wall can be lined or rigid. Unlike current methods,
reflection from the duct openings is taken into account, as well as the presence of the
evanescent modes. Forward, as well as backward (i.e., from the rear of the engine),
external radiation is computed.
The development of analytical expressions for the sound field resulting from both the
fan loading noise and the control sources is presented. Two fan models are described. The
first model uses spinning line sources with radially distributed strength to model the
loading force that the fan blades exert on the medium. The second model uses radial
arrays of spinning point dipoles to simulate the generation of fan modes of specific modal
amplitudes. It is shown that these fan models can provide a reasonable approximation of
actual engine fan noise in the instance when the modal amplitude of the propagating
modes or the loading force distribution on the fan blades, is known.
Sample cases of active noise control are performed to demonstrate the feasibility of
the model. The results from these tests indicate that this model 1) is conducive to more
realistic studies of active control of fan noise on ultra high bypass turbofan engines
because it accounts for the presence of evanescent modes and for interference between
inlet and outlet radiation, which were shown to have some impact on the performance of
the active control system; 2) is very useful because it allows monitoring of any region of
the acoustic field; 3) is computationally fast, and therefore suitable to conduct parametric
Finally, the potential that active noise control techniques have for reducing fan noise
on an ultra high bypass turbofan engine is investigated. Feedforward control algorithms
are simulated. Pure active control techniques, as well as hybrid (active/passive) control
techniques, are studied. It is demonstrated that active noise control has the potential to
reduce substantially, and over a relatively large far field sector, the fan noise radiated by
an ultra high bypass turbofan engine. It is also shown that a hybrid control system can
achieve significantly better levels of noise reduction than a pure passive or pure active
control system, and that its optimum solution is more robust than the one achieved with a
pure active control system.
The model has shown to realistically predict engine acoustic behavior and is thus
likely to be a very useful tool for designing active noise control systems for ultra high
bypass turbofan engines.
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28.8 Modem 56K Modem ISDN (64 Kb) ISDN (128 Kb) Higher-speed Access 00_etd.pdf 43.99 Kb 00:00:12 00:00:06 00:00:05 00:00:02 < 00:00:01 appendixa.pdf 8.99 Kb 00:00:02 00:00:01 00:00:01 < 00:00:01 < 00:00:01 appendixb.pdf 17.86 Kb 00:00:04 00:00:02 00:00:02 00:00:01 < 00:00:01 chapter1.pdf 88.23 Kb 00:00:24 00:00:12 00:00:11 00:00:05 < 00:00:01 chapter2.pdf 104.58 Kb 00:00:29 00:00:14 00:00:13 00:00:06 < 00:00:01 chapter3.pdf 137.93 Kb 00:00:38 00:00:19 00:00:17 00:00:08 < 00:00:01 chapter4.pdf 142.00 Kb 00:00:39 00:00:20 00:00:17 00:00:08 < 00:00:01 chapter5.pdf 2.41 Mb 00:11:09 00:05:44 00:05:01 00:02:30 00:00:12 chapter6.pdf 491.98 Kb 00:02:16 00:01:10 00:01:01 00:00:30 00:00:02 chapter7.pdf 12.10 Kb 00:00:03 00:00:01 00:00:01 < 00:00:01 < 00:00:01 references.pdf 29.05 Kb 00:00:08 00:00:04 00:00:03 00:00:01 < 00:00:01 vita.pdf 2.75 Kb < 00:00:01 < 00:00:01 < 00:00:01 < 00:00:01 < 00:00:01
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