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At least 91 records · Page 5

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NASA NTRS1994

Analytical investigation of adaptive control of radiated inlet noise from turbofan engines

An analytical model has been developed to predict the resulting far field radiation from a turbofan engine inlet. A feedforward control algorithm was simulated to predict the controlled far field radiation from the destructive combination of fan noise and secondary control sources. Numerical results were developed for two system configurations, with the resulting controlled far field radiation patterns showing varying degrees of attenuation and spillover. With one axial station of twelve control sources and error sensors with equal relative angular positions, nearly global attenuation is achieved. Shifting the angular position of one error sensor resulted in an increase of spillover to the extreme sidelines. The complex control inputs for each configuration was investigated to identify the structure of the wave pattern created by the control sources, giving an indication of performance of the system configuration. It is deduced that the locations of the error sensors and the control source configuration are equally critical to the operation of the active noise control system.

Risi, John D.↗

NASA NTRS1993

Preliminary experiments on active control of fan noise from a turbofan engine

In the preliminary experiments reported here, active acoustic sources positioned around the circumference of a turbofan engine were used to control the fan noise radiated forward through the inlet. The main objective was to demonstrate the potential of active techniques to alleviate the noise pollution that will be produced by the next generation of larger engines. A reduction of up to 19 dB in the radiation directivity was demonstrated in a zone that encompasses a 30-deg angle, near the error sensor, while spillover effects were observed toward the lateral direction. The simultaneous control of two tones was also demonstrated using two identical controllers in a parallel control configuration.

Thomas, R. H.↗

NASA NTRS2003

Fan Noise Control Using Herschel-quincke Resonators

The research effort proposed for this NASA NRA is mainly experimental. In addition, Virginia Tech is working in partnership with Goodrich Aerospace, Aerostructures Group for the analytical development needed to support the experimental endeavor, i.e. model development, design, and system studies. In this project, Herschel-Quincke (HQ)liner technology experiments will be performed at the NASA Glenn Active Noise Control Fan (ANCF) facility. A schematic of both inlet and aft HQ-liner systems installed in the ANCF rig as well as a picture of the Glenn facility is shown. The main goal is to simultaneously test in both the inlet and bypass duct sections. The by-pass duct will have HQ-systems in both the inner and outer duct walls. The main advantages of performing tests at the ANCF facility are that the effect of the inlet HQ-system on the by-pass HQ-system and vice versa, can be accurately determined from the in-duct modal data. Another significant advantage is that it offers the opportunity to assess (on a common basis) the proposed noise reduction concept on the ANCF rig which in the past has been used for assessing other active and passive noise reduction strategies.

Burdisso, Ricardo A.↗

NASA NTRS2004

Generation of Higher Order Modes in a Rectangular Duct

Advanced noise control methodologies to reduce sound emission from aircraft engines take advantage of the modal structure of the noise in the duct. This noise is caused by the interaction of rotor wakes with downstream obstructions such as exit guide vanes. Mode synthesis has been accomplished in circular ducts and current active noise control work has made use of this capability to cancel fan noise. The goal of the current effort is to examine the fundamental process of higher order mode propagation through an acoustically treated, curved duct. The duct cross-section is rectangular to permit greater flexibility in representation of a range of duct curvatures. The work presented is the development of a feedforward control system to generate a user-specified modal pattern in the duct. The multiple-error, filtered-x LMS algorithm is used to determine the magnitude and phase of signal input to the loudspeakers to produce a desired modal pattern at a set of error microphones. Implementation issues, including loudspeaker placement and error microphone placement, are discussed. Preliminary results from a 9-3/8 inch by 21 inch duct, using 12 loudspeakers and 24 microphones, are presented. These results demonstrate the ability of the control system to generate a user-specified mode while suppressing undesired modes.

Gerhold, Carl H.↗

NASA NTRS2003

Interaction Metrics for Feedback Control of Sound Radiation from Stiffened Panels

Interaction metrics developed for the process control industry are used to evaluate decentralized control of sound radiation from bays on an aircraft fuselage. The metrics are applied to experimentally measured frequency response data from a model of an aircraft fuselage. The purpose is to understand how coupling between multiple bays of the fuselage can destabilize or limit the performance of a decentralized active noise control system. The metrics quantitatively verify observations from a previous experiment, in which decentralized controllers performed worse than centralized controllers. The metrics do not appear to be useful for explaining control spillover which was observed in a previous experiment.

Cabell, Randolph H.↗

NASA NTRS1993

Preliminary analysis of amplitude and phase fluctuations in the JAPE multiple tone data to distances of 500 meters

The JAPE short range data provide a good opportunity for studying phase and amplitude fluctuations of acoustic signals in the atmosphere over distances of several hundred meters. Several factors contribute to the usefulness of these data: extensive meteorological measurements were made, controlled sources were used, the data were recorded with a high dynamic range digital system that preserved phase information and a significant number of measurement points were obtained allowing both longitudinal and transverse studies. Further, Michigan Tech, in cooperation with the U.S. Army TARDEC, has developed phase tracking algorithms for studying vehicle acoustic signals. These techniques provide an excellent tool for analyzing the amplitude and phase fluctuations of the JAPE data. The results of studies such as those reported here have application at several levels: the mechanisms of signal amplitude and phase fluctuations in propagating acoustic signals are not well understood nor are the mathematical models highly developed, acoustic arrays depend strongly on signal coherence and signal amplitude stability in order to perform to their design specifications and active noise control implementation in regions considerably removed from the primary and secondary sources depends upon signal amplitude and phase stability. Work reported here is preliminary in nature but it does indicate the utility of the phase tracking and amplitude detection algorithms. The results obtained indicate that the phase fluctuations of the JAPE continuous multiple tone data (simultaneous transmission of 80, 200 and 500 Hz) are in general agreement with existing theories but the amplitude fluctuations are seen to be less well behaved and show less consistency.

Rogers, James↗

NASA NTRS1999

Electrical Properties and Power Considerations of a Piezoelectric Actuator

This paper assesses the electrical characteristics of piezoelectric wafers for use in aeronautical applications such as active noise control in aircraft. Determination of capacitive behavior and power consumption is necessary to optimize the system configuration and to design efficient driving electronics. Empirical relations are developed from experimental data to predict the capacitance and loss tangent of a PZT5A ceramic as nonlinear functions of both applied peak voltage and driving frequency. Power consumed by the PZT is the rate of energy required to excite the piezoelectric system along with power dissipated due to dielectric loss and mechanical and structural damping. Overall power consumption is thus quantified as a function of peak applied voltage and driving frequency. It was demonstrated that by incorporating the variation of capacitance and power loss with voltage and frequency, satisfactory estimates of power requirements can be obtained. These relations allow general guidelines in selection and application of piezoelectric actuators and driving electronics for active control applications.

Jordan, T.↗

NASA NTRS1986

A study of methods to predict and measure the transmission of sound through the walls of light aircraft

Progress was made in the following areas: development of a numerical/empirical noise source identification procedure using bondary element techniques; identification of structure-borne noise paths using structural intensity and finite element methods; development of a design optimization numerical procedure to be used to study active noise control in three-dimensional geometries; measurement of dynamic properties of acoustical foams and incorporation of these properties in models governing three-dimensional wave propagation in foams; and structure-borne sound path identification by use of the Wigner distribution.

Bernhard, R. J.↗

NASA NTRS1986

A study of methods to predict and measure the transmission of sound through the walls of light aircraft

Several research investigations are discussed. The development of a numerical/empirical noise source identification procedure using boundary element techniques, the identification of structure-borne paths using structural intensity and finite element methods, the development of a design optimization numerical procedure to be used to study active noise control in three-dimensional geometries, and the measurement of the dynamic properties of acoustical foams and the incorporation of these properties in models governing three-dimensional wave propagation in foams are discussed.

Bernhard, R. J.↗

NASA NTRS1988

A study of methods to predict and measure the transmission of sound through the walls of light aircraft

The objectives are: measurement of dynamic properties of acoustical foams and incorporation of these properties in models governing three-dimensional wave propagation in foams; tests to measure sound transmission paths in the HP137 Jetstream 3; and formulation of a finite element energy model. In addition, the effort to develop a numerical/empirical noise source identification technique was completed. The investigation of a design optimization technique for active noise control was also completed. Monthly progress reports which detail the progress made toward each of the objectives are summarized.

Bernhard, R. J.↗

NASA NTRS1991

Active sound attenuation across a double wall structure

The possibility of achieving significant local and global sound attenuation across a flat double wall is demonstrated. It is also shown that sound can be prevented from entering the interior of a cabinlike environment. The approach used is unlike established active noise control techniques.

Grosveld, Ferdinand W.↗

NASA NTRS1993

Rotating rake design for unique measurement of fan-generated spinning acoustic modes

In light of the current emphasis on noise reduction in subsonic aircraft design, NASA has been actively studying the source of and propagation of noise generated by subsonic fan engines. NASA/LeRC has developed and tested a unique method of accurately measuring these spinning acoustic modes generated by an experimental fan. This mode measuring method is based on the use of a rotating microphone rake. Testing was conducted in the 9 x 15 Low-speed Wind Tunnel. The rotating rake was tested with the Advanced Ducted Propeller (ADP) model. This memorandum discusses the design and performance of the motor/drive system for the fan-synchronized rotating acoustic rake. This novel motor/drive design approach is now being adapted for additional acoustic mode studies in new test rigs as baseline data for the future design of active noise control for subsonic fan engines. Included in this memorandum are the research requirements, motor/drive specifications, test performance results, and a description of the controls and software involved.

Konno, Kevin E.↗

NASA NTRS1996

Comparison of Predicted Low Speed Fan Rotor/Stator Interaction Modes to Measured

The V072 Rotor Wake/Stator Interaction Code is widely used as a state-of-the-art prediction code. This paper validates the code by comparing experimentally measured mode levels to those predicted by V072. The experimental mode levels were measured by the Rotating Rake system installed on the 48 inch Active Noise Control Fan at NASA Lewis Research Center. V072 predicted mode levels by inputting the actual wake profiles of the ANCF rotor measured by a 2-component hotwire. The mode levels were also predicted from the V072 wake models. V072 reasonably predicts the mode levels within the design limits of the code.

Sutliff, Daniel L.↗

NASA NTRS1999

Coupling of Low Speed Fan Stator Vane Unsteady Pressures to Duct Modes: Measured versus Predicted

Uniform-flow annular-duct Green's functions are the essential elements of the classical acoustic analogy approach to the problem of computing the noise generated by rotor-stator interaction inside the fan duct. This paper investigates the accuracy of this class of Green's functions for predicting the duct noise levels when measured stator vane unsteady surface pressures are used as input to the theoretical formulation. The accuracy of the method is evaluated by comparing the predicted and measured acoustic power levels for the NASA 48 inch low speed Active Noise Control Fan. The unsteady surface pressures are measured,by an array of microphones imbedded in the suction and pressure sides of a single vane, while the duct mode levels are measured using a rotating rake system installed in the inlet and exhaust sections of the fan duct. The predicted levels are computed using properly weighted integrals of measured surface pressure distribution. The data-theory comparisons are generally quite good particularly when the mode cut-off criterion is carefully interpreted. This suggests that, at least for low speed fans, the uniform-flow annular-duct Green's function theory can be reliably used for prediction of duct mode levels if the cascade surface pressure distribution is accurately known.

Sutliff, Daniel L.↗

NASA NTRS2001

Fan Noise Reduction: An Overview

Fan noise reduction technologies developed as part of the engine noise reduction element of the Advanced Subsonic Technology Program are reviewed. Developments in low-noise fan stage design, swept and leaned outlet guide vanes, active noise control, fan flow management, and scarfed inlet are discussed. In each case, a description of the method is presented and, where available, representative results and general conclusions are discussed. The review concludes with a summary of the accomplishments of the AST-sponsored fan noise reduction research and a few thoughts on future work.

Envia, Edmane↗

NASA NTRS2002

Acoustic Benefits of Stator Sweep and Lean for a High Tip Speed Fan

A model high-speed fan stage was acoustically tested in the NASA Glenn 9- by 15-Foot Low Speed Wind Tunnel at takeoff/approach flight conditions. The fan was designed for a corrected rotor tip speed of 442 m/s (1450 ft/s), and had a powered core, or booster stage, giving the model a nominal bypass ratio of 5. The model also had a simulated engine pylon and nozzle bifurcation contained within the bypass duct. The fan was tested with three stator sets to evaluate acoustic benefits associated with a swept and leaned stator and with a swept integral vane/frame stator which incorporated some of the swept and leaned features as well as eliminated some of the downstream support structure. The baseline fan with the wide chord rotor and baseline stator approximated a current GEAE CF6 engine. A flyover effective perceived noise level (EPNL) code was used to generate relative EPNL values for the various configurations. Flyover effective perceived noise levels (EPNL) were computed from the model data to help project noise benefits. A tone removal study was also performed. The swept and leaned stator showed a 3 EPNdB reduction at lower fan speeds relative to the baseline stator; while the swept integral vane/frame stator showed lowest noise levels at intermediate fan speeds. Removal of the bypass blade passage frequency rotor tone (BPF) showed a 4 EPNdB reduction for the baseline and swept and leaned stators, and a 6 EPNdB reduction for the swept integral vane/ frame stator. Therefore, selective tone removal techniques such as active noise control and/or tuned liner could be particularly effective in reducing noise levels for certain fan speeds.

Woodward, Richard P.↗

NASA NTRS2002

Low-Speed Fan Noise Reduction With Trailing Edge Blowing

An experimental proof-of-concept test was conducted to demonstrate reduction of rotor-stator interaction noise through rotor-trailing edge blowing. The velocity deficit from the viscous wake of the rotor blades was reduced by injecting air into the wake from a trailing edge slot. Composite hollow rotor blades with internal flow passages were designed based on analytical codes modeling the internal flow. The hollow blade with interior guide vanes creates flow channels through which externally supplied air flows from the root of the blade to the trailing edge. The impact of the rotor wake-stator interaction on the acoustics was also predicted analytically. The Active Noise Control Fan, located at the NASA Glenn Research Center, was used as the proof- of-concept test bed. In-duct mode and farfield directivity acoustic data were acquired at blowing rates (defined as mass supplied to trailing edge blowing system divided by fan mass flow) ranging from 0.5 to 2.0 percent. The first three blade passing frequency harmonics at fan rotational speeds of 1700 to 1900 rpm were analyzed. The acoustic tone power levels (PWL) in the inlet and exhaust were reduced 11.5 and -0.1, 7.2 and 11.4, 11.8 and 19.4 PWL dB, respectively. The farfield tone power levels at the first three harmonics were reduced 5.4, 10.6, and 12.4 dB PWL. At selected conditions, two-component hotwire and stator vane unsteady surface pressures were acquired. These measurements illustrate the physics behind the noise reduction.

Sutliff, Daniel L.↗

NASA NTRS2005

Technologies for Turbofan Noise Reduction

An overview presentation of NASA's engine noise research since 1992 is given for subsonic commercial aircraft applications. Highlights are included from the Advanced Subsonic Technology (AST) Noise Reduction Program and the Quiet Aircraft Technology (QAT) project with emphasis on engine source noise reduction. Noise reduction goals for 10 EPNdB by 207 and 20 EPNdB by 2022 are reviewed. Fan and jet noise technologies are highlighted from the AST program including higher bypass ratio propulsion, scarf inlets, forward-swept fans, swept/leaned stators, chevron nozzles, noise prediction methods, and active noise control for fans. Source diagnostic tests for fans and jets that have been completed over the past few years are presented showing how new flow measurement methods such as Particle Image Velocimetry (PIV) have played a key role in understanding turbulence, the noise generation process, and how to improve noise prediction methods. Tests focused on source decomposition have helped identify which engine components need further noise reduction. The role of Computational AeroAcoustics (CAA) for fan noise prediction is presented. Advanced noise reduction methods such as Hershel-Quincke tubes and trailing edge blowing for fan noise that are currently being pursued n the QAT program are also presented. Highlights are shown form engine validation and flight demonstrations that were done in the late 1990's with Pratt & Whitney on their PW4098 engine and Honeywell on their TFE-731-60 engine. Finally, future propulsion configurations currently being studied that show promise towards meeting NASA's long term goal of 20 dB noise reduction are shown including a Dual Fan Engine concept on a Blended Wing Body aircraft.

Huff, Dennis↗