Electrical audio signal processing systems and devices – Acoustical noise or sound cancellation – Within duct
Reexamination Certificate
1997-04-18
2001-03-13
Chang, Vivian (Department: 2747)
Electrical audio signal processing systems and devices
Acoustical noise or sound cancellation
Within duct
C381S071700
Reexamination Certificate
active
06201872
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of active control of axial fan rotor-stator interaction noise.
2. Prior Art
Communities located adjacent to commercial airports are often exposed to excessive and annoying noise generated from landing, takeoff and flyover maneuvers.
FIG. 1
is a schematic cross-section of the most common propulsion system used in commercial high-bypass-ratio turbofan engines (see
Turbomachinery Noise,
Groeneweg, J. F., Sofrin, T. G. and Rice, E. J., NASA Reference Publication 1258, Vol. 1, WDRC Technical Report 90-3052, August 1991). The various internal noise sources are identified as well as locations of passive sound absorbing treatment.
FIG. 2
displays predicted flyover maximum perceived noise levels generated from separate engine components of a typical commercial turbofan engine (taken from
Energy Efficient Engine Propulsion System-Aircraft Integration Evaluation,
Owens, R. E., NASA CR-159488, 1979). Observe that for this engine, the maximum perceived noise levels are dominated by fan inlet and exhaust sources.
FIG. 3
displays sound power spectra generated from typical turbomachinery operating at subsonic and supersonic tip speeds. At subsonic tip speeds, large tones are observed at harmonics of the rotor blade-passage frequencies (BPF) in contrast to the spectra at supersonic tip speeds where very large number of tones are generated from rotating shock waves and associated nonlinearities at frequencies both above and below the engine blade passing frequency (BPF).
Despite many years of intensive research, jet engine noise remains as one of the major pollution problems facing communities located near civilian airports. This is not surprising because the suppression of jet engine noise is inherently complex, involving the interaction between different physical phenomena such as (1) complicated radial and spinning modes convecting in three-dimensional flows containing transverse velocity and thermal gradients which refract the sound, (2) subsonic and supersonic accelerating mean flows, (3) combustion noise, (4) acoustic wave propagation and resonance and (5) natural or forced hydrodynamic and acoustic instabilities. As a consequence of the complexity of these mechanisms and their (nonlinear) interactions, very few “practical” guidelines have evolved to allow the engine designer to predict, let alone control, jet noise inlet and exhaust noise in a given design.
The need to improve aircraft performance and efficiency while decreasing community noise taxes the acoustic suppression capability of the sound absorbing treatment that line the ducts of turbofan engines. New ultra-high-bypass engines with shorter inlet and exhaust ducts have less room for acoustic treatment. Thus, more effective treatment is required than is currently available. Much of the treatment used currently has a very limited frequency range over which it is effective, that is, it is only effective for an single tone. If the treatment could be effective for several or all tones at the same time, than all of the treatment area would be available for each tone.
Active sound attenuation is a relatively old concept that has received considerable attention in recent years, primarily because the increasing availability of fast programmable signal processing hardware has made these systems viable for audio frequency applications. Although active noise control technology has been demonstrated to be very successful in many industrial noise control applications, it has been not been used in applications that are sensitive to the severe weight, size, ruggedness, reliability and energy constraints required in the control of excessive commercial jet engine noise.
BRIEF SUMMARY OF THE INVENTION
The present invention is based on two novel and unique active noise control concepts to achieve significant reduction of the intense rotor-stator interaction tones generated in commercial high bypass turbofan engines and commercial HVAC axial fans. In accordance with the first concept, arrays of active control sound sources are installed on the inlet side (upstream) and on the exhaust side (downstream) of the stator vanes of an axial fan. The sound fields radiated from the fan inlet and exhaust are canceled simultaneously by driving the arrays of active control sound sources with the appropriate amplitude and phase.
The second concept is based upon an active control sound absorption scheme. Arrays of active control Helmholtz resonators are installed between the fan inlet and the rotors of an axial fan to absorb rotor-stator generated tones. The sound fields radiated from the fan inlet are canceled by driving the arrays of active control resonators with the appropriate amplitude and phase. With a duplicate arrangement, the system would be extended to cancel the modes in the exhaust duct as well.
An adaptively controlled dipole sound source system has been tested and shown to provide 29 dB of attenuation in the inlet and 19 dB in the exhaust of the cosine component of the (2 0) rotor-stator interaction tone in axial fan facility. The novelty of the control scheme is that by utilizing knowledge of the mode transmitted in the duct, the complexity of the control algorithm is reduced dramatically. Furthermore, since the system is configured to only generate the desired modes, one can expect superior performance since unwanted plane-waves and other modes will not be generated.
REFERENCES:
patent: 3936606 (1976-02-01), Wanke
patent: 4044203 (1977-08-01), Swinbanks
patent: 4109108 (1978-08-01), Coxon et al.
patent: 4122303 (1978-10-01), Chaplin et al.
patent: 4372110 (1983-02-01), Cheng
patent: 4473906 (1984-09-01), Warnaka et al.
patent: 4589133 (1986-05-01), Swinbanks
patent: 4669122 (1987-05-01), Swinbanks
patent: 4677676 (1987-06-01), Eriksson
patent: 4677677 (1987-06-01), Eriksson
patent: 4965832 (1990-10-01), Edwards et al.
patent: 5018202 (1991-05-01), Takahashi et al.
patent: 5060271 (1991-10-01), Geddes
patent: 5088575 (1992-02-01), Eriksson
patent: 5097923 (1992-03-01), Ziegler et al.
patent: 5119427 (1992-06-01), Hersh et al.
patent: 5146505 (1992-09-01), Pfaff et al.
patent: 5172416 (1992-12-01), Allie et al.
patent: 5478199 (1995-12-01), Gliebe
patent: 5584447 (1996-12-01), Pla
“Active Noise Cancellation In Ducts In The Presence Of Higher Order Modes”, Goodman et al., Digisonix, Inc.
“Active Cancellation Of Higher Order Modes In A Duct Using Recursively-Coupled Multi-Channel Adaptive Control System”, Rubenstein et al., Inter-Noise, Jul. 1992.
“Number Of Error Microphones For Multi-Modal Cancellation”, Baumann et al., Inter-Noise, Jul. 1992.
“Active Adaptive Sound Control In A Duct: A Computer Simulation”, Burgess, J. Acoust. Soc. Am. 70(3), Sep. 1981.
“Active Systems For Sound Attenuation In Ducts”, Tichy, IEEE 1988.
“Development Of The Filtered-U Algorithm For Active Noise Control”, Eriksson, J. Acoust. Soc. Am. 89(1), Jan. 1991.
Heidelberg Larry
Hersh Alan S.
Walker Bruce E.
Blakeley Sokoloff Taylor & Zafman LLP
Chang Vivian
Hersh Acoustical Engineering, Inc.
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