Title page for ETD etd-110499-180010

Type of Document Dissertation
Author Hutcheson, Florence Vanel
Author's Email Address f.v.hutcheson@larc.nasa.gov
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
  • turbofan engine
  • fan noise
  • active control
Date of Defense 1999-10-14
Availability unrestricted
An 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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