Theoretical implications of Active Noise Control for turbofan engines

Kraft, R. E.; Kontos, Karen

doi:10.2514/6.1993-4355

Cited by 11 publications

(3 citation statements)

References 3 publications

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“…The large, low-speed tan is also used for active noise control experiments. Two approaches are being explored: cancellation in the tan ducts alter generation [10], and modification at the source. e.g.. the stator vane surface pressures [11].…”

Section: Ac11ve Controlmentioning

confidence: 99%

Advanced Subsonic Aircraft Engine Noise Reduction Research

GROENEWEG

2024

Noise Control - The Next 25 Years

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Engine noise reduction research currently underway in the NASA Advanced Subsonic Technology Noise Reduction Program is described. Emphasis Is on noise reduction technology for high to ultra-high bypass ratio turbofan engines which will dominate the airline fleets early in the 21 st century. In terms of noise components, primary emphasis is on the fan with secondary effort on the jet for engines at the lower end of the bypass ratio range. The approach to fan noise prediction consists of modeling the chain of physical processes beginning with flow disturbances on fan blades and ending with far field sound levels. For the jet, CFD solutions for the nozzle geometries are couplele combined aeroacoustic source/radiation models. 0n the experimental side, realistic models at fans. nacelles, and nozzles are tested in aeroaooustic wind tunnel} Comparisons of predicted and measured noise levels are presented as indicators 01 progress toward developing improved low-noise design toois. The challenges of applying active control concepts to turbofan noise are discussed including both cancellation and source modification approaches.

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Section: Ac11ve Controlmentioning

confidence: 99%

Advanced Subsonic Aircraft Engine Noise Reduction Research

GROENEWEG

2024

Noise Control - The Next 25 Years

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“…Unfortunately, introducing this number of transducers into the engine duct incurs a significant weight penalty that is likely to prohibit the use of this technology. The predicted and measured reductions in sound power at the blade passing frequency obtained using fewer, more realistic, numbers of sources and sensors, say O(10 1 ), have generally been limited to a just a few decibels [2,3,4,5]. This is principally because of the effects of modal spillover whereby modes in additional to those already present are excited thereby significantly degrading active control performance.…”

Section: Suitability Of Buzz-saw Noise For Active Controlmentioning

confidence: 99%

Active Control of Low Frequency Buzz-Saw Tones; Theory and Experiment

Joseph

Wilkinson²

2007

International Journal of Aeroacoustics

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This paper discusses some theoretical and experimental issues related to the active control of buzz-saw tones radiated from an aircraft engine inlet at takeoff. Buzz-saw tones occur when the rotor tip speed becomes supersonic. It arises due to the formation of shocks at the blade tips, which then propagate non-linearly along the engine duct. Buzz-saw noise comprises a series of tones harmonically related to the shaft rotation frequency (Engine Orders). Moreover, it has been shown that the noise at each Engine Order comprises just one single spinning mode. Whilst there has been considerable work aimed at assessing the feasibility of active control for reducing the tones due to rotor-stator interaction, buzz-saw noise has been overlooked. This is surprising given the low frequencies at which Buzz-Saw noise occurs, and its simple modal content, which both suggest that buzz-saw noise is particularly suited to active control. This paper describes various control strategies for reducing buzz-saw noise. The paper concludes with the results of a laboratory experiment aimed at demonstrated experimentally the effectiveness with which a single spinning mode, characteristic of an EO = 3 buzz-saw tone, can be controlled. Reductions in excess of 14dB are reported at some frequencies.

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“…More recently, Kraft and Kontos 4 developed an analytical model to explore the theoretical implications of active control of turbofan engine noise. The secondary control source of their model is a single axial station comprised of electromagnetic sources located in the engine duct, flush with the outer wall of the inlet duct, coupled to the duct by a short horn.…”

Section: Introductionmentioning

confidence: 99%

Analytical investigation of active control of radiated inlet fan noise

Risi

Burdisso

Fuller

1996

The Journal of the Acoustical Society of America

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An analytical model has been developed to study the potential of active noise control techniques for reducing radiated tonal inlet noise from turbofan engines. The analytical model consists of multiple control sources placed in the periphery of the engine inlet duct which inject antinoise into the duct to destructively interfere with the tonal sound field generated by the fan. The development of the analytical expressions of the radiated sound fields due to both the disturbance and the control sources is based on duct modal expansion. Attenuation of the radiated sound field is accomplished using a multiple-channel feedforward control approach. Control signals are calculated to minimize the pressure disturbance at desired error sensor locations and are then used to determine the controlled radiated sound field. The model is used to evaluate the performance of the control system for single and multiple circumferential arrays of control sources. The model can be extended for use in design optimization. Sample results are presented to illustrate the predicted sound attenuations. © 1996 Acoustical Society of America.PACS numbers: 43.40.Vn INTRODUCTIONNoise is a significant negative factor associated with the modern commercial airline industry. When turbojets were first introduced, the primary source of noise was from the engine exhaust in the take-off configuration. The high power settings required for climb-out created a broadband exhaust noise that dominated in the vicinity of the take-off path of the aircraft. During approach, when the engine is at or near idle condition, the discrete high-frequency whine of the compressors becomes dominant.1 As engines evolved from turbojet to primarily turbofan cycles, fan noise has become an increasingly larger contributor of total engine noise. The impending use of ultrahigh bypass ratio engines will result in an even greater fan noise component at lower frequencies. Noise reduction techniques to date consist primarily of passive liners. However, the shorter inlet ducts inherent to the ultrahigh bypass engines and the lower blade passage frequencies expected for these engines will make passive attenuation of the inlet fan noise even more difficult. In order to meet forecast noise level requirements, the use of active noise control techniques may have the potential to overcome these problems.The concept of active sound control, or antinoise as it is sometimes referred, is attributed to Lueg.2 Although Lueg's patent is almost 60 years old, only in the past 20 years has widespread use of active control begun to emerge. Very recently, an experimental effort has been undertaken by Thomas et al. 3 to investigate the potential of active noise control approaches to reduce fan noise from a turbofan engine. In this work, the tonal noise radiated by the fan of a Pratt and Whitney JT15D turbofan engine was controlled using an adaptive feedforward control algorithm. The control source transducers were electromagnetic loudspeakers attached to the engine inlet duct through exponential horn...

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Theoretical implications of Active Noise Control for turbofan engines

Cited by 11 publications

References 3 publications

Advanced Subsonic Aircraft Engine Noise Reduction Research

Advanced Subsonic Aircraft Engine Noise Reduction Research

Active Control of Low Frequency Buzz-Saw Tones; Theory and Experiment

Analytical investigation of active control of radiated inlet fan noise

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