Joe W. Posey

Duct Liner Optimization for Turbomachinery Noise Sources

An acoustical field theory for axisymmetric multisectioned duct liners is combined with a numerical minimization algorithm to predict optimal one‐ and two‐sectioned liner configurations producing maximum sound attenuation. Optimal inlet liner impedance properties calculated by this method are presented for a research compressor operating at about 0.4 Mach number. Kemp‐Sears theory is used to describe the rotor/stator viscous wake interaction effects. Comparisons with data presented for point and plane‐wave sources indicate that optimal liners for complex turbomachinery sources cannot be easily inferred from data based on these simpler source models.

Noise Mechanisms in the Inflation of the Automotive Safety Air Bag

Free‐field noise from a compressed‐gas air bag inflator was recorded and spectrally analyzed. Tests were run with different types of silencing devices inserted in the manifolding, and with and without the bag attached. Comparisons between the noise spectra obtained in these tests permitted the identification of different mechanisms of noise generation. The largest peak in the spectrum was generally below 20 Hz and is due to a monopole‐type of source associated with the overall discharge of gas from the inflator system. Other noise sources are associated with the motion of the surface of the bag, “organ‐pipe” sources within the manifolding, and broadband jet noise associated with the flow of gas through the diffuser slots into the air bag.

A fast method of deriving the Kirchhoff formula for moving surfaces

The Kirchhoff formula for a moving surface is very useful in many wave propagation problems, particularly in the prediction of noise from rotating machinery. Several publications in the last two decades have presented derivations of the Kirchhoff formula for moving surfaces in both time and frequency domains. The method presented here, originally developed by Farassat and Myers in time domain, is both simple and direct. It is based on generalized function theory and the useful concept of imbedding the problem in the unbounded three‐dimensional space. An inhomogeneous wave equation is derived with source terms that involve Dirac delta functions with their supports on the moving data surface. This wave equation is then solved using the simple free space Green’s function of the wave equation resulting in the Kirchhoff formula. The algebraic manipulations are minimal and simple. The derivation does not require the Green’s theorem in four dimensions and there is no ambiguity in the interpretation of any terms ...

Jet noise from ultrahigh bypass turbofan engines

Modern commercial jet transport aircraft are powered by turbofan engines. Thrust from a turbofan engine is derived in part from the exhaust of a ducted fan, which may or may not be mixed with the core exhaust before exiting the nacelle. The historical trend has been toward ever higher bypass ratios (BPRs). The BPR is the ratio of air mass passing through the fan to that going through the core. The higher BPR engines can be more efficient and quieter. In general, a higher BPR results in lower average exhaust velocities and less jet noise. In order to address a scarcity of noise data for BPRs greater than 6, an extensive database collection effort was undertaken using the Jet Engine Simulator in NASA Langley’s Low Speed Aeroacoustic Wind Tunnel. Forward flight simulations of Mach 0.1, 0.2, and 0.28 were used with BPRs of 5, 8, 11, and 14. Data was taken over the entire operating line of the simulated engines along with parametric deviations to provide a complete set of sensitivity measurements. The results ...

Aerodynamic Noise: An Introduction for Physicists and Engineers

This article reviews Aerodynamic Noise: An Introduction for Physicists and Engineers by Tarit Bose , New York, NY, 2013. 165 pp. Price:

Aircraft noise prediction.

89.95 (hardcover). ISBN: 978-1-4614-5018-4

Overview of revolutionary aircraft for quiet communities workshop

Noise has been an issue for airport communities and passengers since the advent of commercial air transport almost a century ago. Impressive gains have been made in aircraft noise control, but expectations are rising and air traffic will at least double in the next 20 years. Also, lighter composite structures pose a challenge for interior noise control. Furthermore, societal expectations for mobility, new technology, demands for carbon footprint minimization, and other environmental imperatives will lead to revolutionary aircraft designs in the future. This tutorial lecture will consider noise from present and future subsonic jet aircraft, rotorcraft, propeller aircraft, and supersonic transports. Noise prediction capabilities will be identified, along with an overview of noise control technology. Acousticians are preparing to predict and control community and interior noise for arbitrary configurations using models based more on first principles, whereas the state‐of‐the‐art is largely semiempirical. It ...

NASA‐sponsored active fan noise control research

At some time in the future, technical advances, environmental imperatives, societal expectations for mobility, and economic drivers will dictate that radically different aircraft will be built and flown. Therefore, aircraft designs will change even if low noise were not one of the environmental imperatives, and acousticians must be aware of the possible directions for aircraft design and the resulting opportunities and challenges for noise control. To address this need, the National Aeronautics and Space Administration sponsored a workshop entitled Revolutionary Aircraft for Quiet Communities in Hampton, VA, 24‐26 July 2007. Twenty‐six talks covered aircraft design, interior noise challenges, airframe noise, propulsion, and aircraft noise prediction. Revolutionary aircraft will employ dramatically improved materials, propulsion systems, and flow control technology to improve efficiency and enhance mobility. Five hours of discussion surfaced many concerns and recommendations, including the increasing need ...

A selected history of duct mode synthesis

The National Aeronautics and Space Administration (NASA) has espoused the vision of developing technology capable of keeping all objectionable aircraft noise within airport boundaries. In order to achieve such an aggressive goal, new aircraft will have to be designed employing quiet propulsion, quiet lift, and quiet drag. Research activities are continuing on all these fronts. Dominant sources of propulsion noise to date on jet‐powered transports have been jet noise and fan noise. As bypass ratios of aircraft turbofan engines have increased to improve fuel efficiency, jet velocities (and therefore jet noise) have decreased, making fan noise the larger contributor in many instances. In NASAs Advanced Subsonic Technology (AST) Program, which ran from 1994 until 2001, several active control strategies for tonal fan noise were investigated. These included rings of wall‐mounted actuators, active impedance control, stator‐mounted actuators, and hybrid active/passive concepts. The most promising approach seems t...

Public acceptance of urban rotorcraft operations

Attempts to attenuate noise propagating down a duct, with or without flow, must recognize that wall boundary conditions permit only certain spatial wave patterns (modes) to exist. The aircraft noise research community began building mode synthesizers at least thirty years ago in order to study duct propagation and radiation phenomena in a laboratory environment. Lockheed Georgia built a spinning mode synthesizer (SMS) for NASA in the 1970s. NASA used its SMS in a circular flow‐duct to validate predictions of mode propagation through constrictions, lined sections, and inlets of various shapes. In the mid‐1970s, Penn State created a mode synthesizer as part of a demonstration of active noise control in a circular, no‐flow duct. NASA sponsored a series of studies in the 1990s aimed at maturing active control technology for ducted fan noise. Each of these active control systems was essentially a mode synthesizer coupled with a control system to cancel fan‐generated noise. NASA is currently building a new mode...