Michael G. Jones

• MSME
• Senior Research Scientist (retired) at National Aeronautics and Space Administration

Acoustic liner samples with rectangular, sharp chamber bends are 3D-printed and tested in the NASA Normal Incidence Tube. The angle of the bend is varied from 0 to 180 degrees. Four different methods are used to predict the impedance behavior of these samples: (1) midline-length assumption, (2) Cummings correction for curved duct bends, (3) Cumming...

This report presents results of a comparison of multiple perforate facesheet impedance prediction models against a large dataset acquired in the NASA Langley Liner Technology Facility. Based on these comparisons one model is selected for further semiempirical enhancements.

This paper presents findings from a study conducted under a challenge of the International Forum for Aviation Research (IFAR), which consists of partners from various national research labs around the world. A series of normal incidence impedance tube tests are performed to identify differences in acoustic impedance for various types of source exci...

Acoustic liners, typically used as a noise control treatment in the engine nacelles of conventional aircraft, are being considered for noise treatment in the proprotor ducts of a vertical takeoff and landing aircraft. This work considers a new optimization method to design an acoustic liner with variable depth cavities for broadband and low-frequen...

A series of normal incidence impedance tube tests are conducted to characterize the facesheet impedance differences between uniformly distributed and nonuniformly tightly packed hole layout patterns, defined here as "hole clustering." These hole clustered samples contain the same number of holes as their uniformly distributed counterparts but have...

An acoustic liner optimization tool is developed for designing two degree of freedom (2DOF) liners with high absorption over a wide range of frequencies and sound pressure levels (SPLs). Two additively manufactured 2DOF liners (one constant and one variable chamber depth) are designed and printed with an embedded perforate layer as the septum. A no...

The potential rise of the Urban Air Mobility market has spurred the design of a new generation of novel aircraft. To aid industry and researchers interested in these types of aircraft, the Revolutionary Vertical Lift Technology project at NASA has developed a fleet of reference vehicles for system studies. A new six-passenger reference vehicle has...

An initial evaluation of variable-depth, slotted-core liners fabricated with conventional, flightworthy components is presented. Liners with two distinct chamber lengths provide significant broadband absorption and their impedances are, to first order, predictable with the NASA impedance prediction code. These liners employ film caps embedded in al...

An active acoustic liner was developed by The Boeing Company in support of a contract with NASA. The design of the active liner is a honeycomb core with a three-layer facesheet (FS): the top and bottom layers are static while the middle layer can move via actuation by an embedded shape memory alloy (SMA) wire. This paper describes experiments perfo...

NASA and ONERA have explored a number of acoustic liner concepts over the last few decades. This paper begins with a brief review regarding conventional liners as well as the recent implementation of multi-degree-of-freedom liners enabled by embedded mesh caps. Six novel liner concepts are presented, along with the accompanying impedance prediction...

Thin, lightweight, and durable broadband acoustic absorbers capable of absorbing sounds over a wide frequency range, especially below 1000 Hz, while also surviving harsh operational conditions such as exposure to sprays of liquid and solid debris and high temperatures are desired for many noise control applications. While today’s commercially avail...

View Video Presentation: https://doi.org/10.2514/6.2021-2243.vid Tests were conducted in the NASA Langley Grazing Flow Impedance Tube (GFIT) to determine the broadband noise reduction capability of a variable facesheet liner. Three uniform liners were designed to achieve sound absorption over distinct frequency regimes at Mach 0.0. Each liner was f...

View Video Presentation: https://doi.org/10.2514/6.2021-2143.vid Results achieved with three acoustic liner configurations are used to evaluate the effects of recent modifications to the NASA Normal Incidence Tube and Grazing Flow Impedance Tube. These include a calibration liner, a wire mesh liner, and a perforate liner. The effects of source type...

The emphasis on increased turbofan fuel efficiency requires advanced turbofan designs that will integrate higher engine bypass ratios and shorter nacelles. The resulting acoustic signature of these designs will have a more broadband character as well as a smaller available area for liner installation. This two-fold impact compels a need for an impr...

The emphasis on increased turbofan fuel efficiency requires advanced turbofan designs that will integrate higher engine bypass ratios and shorter nacelles. The resulting acoustic signature of these designs will have a more broadband character as well as a smaller available area for liner installation. This two-fold impact compels a need for an impr...

The attenuation of fan tones remains an important aspect of fan noise reduction for high bypass ratio turbofan engines. However, as fan design considerations have evolved, the simultaneous reduction of broadband fan noise levels has gained interest. Advanced manufacturing techniques have also opened new possibilities for the practical implementatio...

This paper presents results for five uniform and two multizone liners based on data acquired in the NASA Langley Grazing Flow Impedance Tube. Two methods, Prony and CHE, are used to educe the impedance spectra for each of these liners for many test conditions. The Prony method is efficient and generally provides accurate results for uniform liners,...

This paper presents the contribution from the German Aerospace Center (DLR) to the first liner benchmark challenge under the framework of the International Forum for Aviation Research (IFAR). Therefore, two sets of acoustically damping wall treatments, called ‘liner samples’, have been produced by additive manufacturing based on the design data pro...

While intrinsic by definition, the impedance measured by impedance eduction has been shown to depend on the direction of the incident waves relative to the mean flow. The purpose of the present work is to evaluate whether part of the observed differences could stem from a biased wavenumber definition made during the impedance eduction process. Comp...

NASA Technical Paper regarding experimental methods employed at NASA Langley Research Center over the last four decades to evaluate acoustic liners

Airborne noise with a dominant low-frequency content (<∼500 Hz) has detrimental effects in many applications, but it is as yet beyond the scope of conventional acoustic noise mitigation techniques using liners, foams, or claddings owing to mass and volume considerations. An alternative approach using liner configurations retaining realistic mass an...

Acoustic liners are commonly used to reduce noise from commercial aircraft engines. Engine liners are placed in the nacelle inlet and aft bypass duct to attenuate the noise radiated from the engine. Traditional engine liners are constructed of a perforated facesheet over a honeycomb structure to create a quarter-wave absorber. With this design, the...

This investigation uses methods based on the Pridmore-Brown and convected Helmholtz equations to study the acoustic behavior of a single-layer, conventional liner fabricated by DLR, German Aerospace Center and tested in the NASA Langley Grazing Flow Impedance Tube. Two key assumptions are explored in this investigation. First, a comparison of resul...

Implementation of the Kumaresan and Tufts algorithm to liner impedance eduction in a duct with shear flow is described. The approach is based on a noncausal model of sound propagation coupled with singular value decomposition to identify the acoustic pressure modes. The performance of the algorithm is evaluated by comparing the educed impedance spe...

The research objective of this paper is to develop an acoustic impedance model for micro-perforate plates. Passive acoustic liners consisting of perforate plates-over-honeycomb structures are a key contributor in the reduction of fan noise propagated through the inlet and aft-fan duct of aircraft engine nacelles. These perforated plates are physica...

A coordinated experimental and numerical simulation effort is carried out to improve our understanding of the physics of acoustic liners in a grazing flow as well our computational aeroacoustics (CAA) method prediction capability. A numerical simulation code based on advanced CAA methods is developed. In a parallel effort, experiments are performed...

The broadband component of fan noise has grown in relevance with the utilization of increased bypass ratio and advanced fan designs. Thus, while the attenuation of fan tones remains paramount, the ability to simultaneously reduce broadband fan noise levels has become more desirable. This paper describes improvements to a previously established broa...

As a result of significant progress in the reduction of fan and jet noise, there is growing concern regarding core noise. One method for achieving core noise reduction is via the use of acoustic liners. However, these liners must be constructed with materials suitable for high temperature environments and should be designed for optimum absorption o...

An impedance eduction theory for a rigid wall duct containing an acoustic liner with an unknown impedance and uniform grazing flow is presented. The unique features of the theory are: 1) non-planar waves propagate in the hard wall sections of the duct, 2) input data consist solely of complex acoustic pressures acquired on a wall adjacent to the lin...

A Williams International FJ44-3A turbofan engine was used to demonstrate the high-speed fan noise reduction potential of a foam-metal liner installed in close proximity to the fan rotor. The engine was tested in the NASA Glenn Research Center's Aeroacoustic Propulsion Laboratory. Two foam-metal liner designs were tested and compared to the hardwall...

The absorption efficiency of acoustic liners used in aircraft engines is characterized by the acoustic impedance. World wide, many grazing flow test rigs and eduction methods are available that provide values for that impedance. However, a direct comparison and assessment of the data of the different rigs and methods is often not possible because t...

A number of methods have been developed at NASA Langley Research Center for eduction of the acoustic impedance of sound-absorbing liners mounted in the wall of a flow duct. This investigation uses methods based on the Pridmore-Brown and convected Helmholtz equations to study the acoustic behavior of a single-layer, conventional liner fabricated by...

A comparative study of four commonly used impedance eduction methods is presented for a range of liner structures and test conditions. Two of the methods are restricted to uniform flow while the other two accommodate both uniform and boundary layer flows. Measurements on five liner structures (a rigid-wall insert, a ceramic tubular liner, a wire me...

As part of a cooperation between ONERA and NASA, the liner impedance eduction methods developed by the two research centers are compared. The NASA technique relies on an objective function built on acoustic pressure measurements located on the wall opposite the test liner, and the propagation code solves the convected Helmholtz equation in uniform...

The acoustic performance of duct liners can be improved by segmenting the treatment. In a segmented liner treatment, one stage of liner reduces the target sound and scatters energy into other acoustic modes, which are attenuated by a subsequent stage. The Curved Duct Test Rig is an experimental facility in which sound incident on the liner can be g...

Results from impedance eduction methods developed by NASA Langley Research Center are used throughout the acoustic liner community. Occasional anomalies persist with these methods at frequencies where the liner produces minimal attenuation. An approach to educe impedance spectra with increased confidence is demonstrated, by combining results from s...

The acoustic performance of a duct liner depends not only on the intrinsic properties of the liner but also on the configuration of the duct in which it is used. A series of experiments is performed in the NASA Langley Research Center Curved Duct Test Rig (at Mach 0.275) to evaluate the effect of duct configuration on the acoustic performance of si...

The accuracy of the Ingard-Myers boundary condition and a recently proposed modified Ingard-Myers boundary condition is evaluated for use in impedance eduction under the assumption of uniform mean flow. The evaluation is performed at three centerline Mach numbers, using data acquired in a grazing flow impedance tube, using both upstream and downstr...

The Interactive Liner Impedance Analysis and Design (ILIAD) tool is a LabVIEW-based software package used to design the composite surface impedance of a series of small-diameter quarter-wavelength resonators incorporating variable depth and sharp bends. Such structures are useful for packaging broadband acoustic liners into constrained spaces for t...

The broadband component of fan noise has grown in relevance with the utilization of increased bypass ratio and advanced fan designs. Thus, while the attenuation of fan tones remains paramount, the ability to simultaneously reduce broadband fan noise levels has become more appealing. This paper describes a broadband acoustic liner optimization study...

Recent trends in aircraft engine design have highlighted the need for acoustic liners that provide broadband sound absorption with reduced liner thickness. Three such liner concepts are evaluated using the NASA normal incidence tube. Two concepts employ additive manufacturing techniques to fabricate liners with variable chamber depths. The first re...

A grazing flow resonator liner impedance model is derived. Analysis of NASA Langley Research Center impedance eduction test data suggests that relatively low speed fluid located near the face-plate housing the resonators is pumped into/out-of the resonator cavities. This motivated the development of a resonator impedance model that assumes fluid is...

This paper outlines a methodology to identify the measurement uncertainty of NASA Langley's Grazing Flow Impedance Tube (GFIT) over its operating range, and to identify the parameters that most significantly contribute to the acoustic impedance prediction. Two acoustic liners are used for this study. The first is a single-layer, perforateover-honey...

A new impedance eduction method is presented and validated against a benchmark method, and the effects of measurement uncertainty errors on the impedances educed with this new method are assessed. Unique features of the new method include the following: 1) the upstream and downstream boundary conditions contain higher-order duct modes, 2) the imped...

Emergent behavior, a subject of much research in biology, sociology, and economics, is a foundational element of Complex Systems Science and is apropos in the design of sensor network systems. To demonstrate engineering for emergent behavior, a novel approach in the design of a sensor/actuator network is presented maintaining optimal noise attenuat...