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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Design of a Dual Waveguide Normal Incidence Tube (DWNIT) Utilizing Energy and Modal Methods

This report investigates the partition design of the proposed Dual Waveguide Normal Incidence Tube (DWNIT). Some advantages provided by the DWNIT are (1) Assessment of coupling relationships between resonators in close proximity, (2) Evaluation of "smart liners", (3) Experimental validation for parallel element models, and (4) Investigation of effects of simulated angles of incidence of acoustic waves. Energy models of the two chambers were developed to determine the Sound Pressure Level (SPL) drop across the two chambers, through the use of an intensity transmission function for the chamber's partition. The models allowed the chamber's lengthwise end samples to vary. The initial partition design (2" high, 16" long, 0.25" thick) was predicted to provide at least 160 dB SPL drop across the partition with a compressive model, and at least 240 dB SPL drop with a bending model using a damping loss factor of 0.01. The end chamber sample transmissions coefficients were set to 0.1. Since these results predicted more SPL drop than required, a plate thickness optimization algorithm was developed. The results of the algorithm routine indicated that a plate with the same height and length, but with a thickness of 0.1" and 0.05 structural damping loss, would provide an adequate SPL isolation between the chambers.

Betts, Juan F.↗
NASA NTRS2019

Evaluation of a Multizone Impedance Eduction Method

A computational study is used to evaluate the PyCHE impedance eduction method developed at the NASA Langley Research Center. This method combines an aeroacoustic duct propagation code based on numerical solution to the convected Helmholtz equation with a global optimizer that uses the Differential Evolution algorithm. The efficacy of this method is evaluated with acoustic pressure data simulated to represent that measured with one-zone, two-zone, and three-zone liners mounted in the NASA Langley Grazing Flow Impedance Tube. The PyCHE method has a normalized impedance error of approximately 0.2 for (uniform) one-zone liners with a length of at least 5”, and produces quite reasonable results for liners as short as 2”. Whereas the impedance of the liner has an effect on eduction accuracy, the amount of attenuation is shown to be the dominant parameter. Similar results are observed for two-zone liners, for which the impedance of each zone is unique. The two-zone results also indicate it is more difficult to accurately educe resistance than reactance, and a zone length of at least 6” (slightly longer than for uniform liners) is needed to limit the normalized error to 0.2. The PyCHE method is also demonstrated to successfully educe the impedances for each zone of a three-zone liner. These results are sufficiently encouraging to warrant the continued usage of the PyCHE impedance eduction method for single and multizone liners.

Jones, M. G.↗
NASA NTRS1982

Acoustic propagation in partially choked converging-diverging ducts

A computer model based on the wave-envelope technique is used to study acoustic propagation in converging-diverging hard walled and lined circular ducts carrying near sonic mean flows. The influences of the liner admittance, boundary layer thickness, spinning mode number, and mean Mach number are considered. The numerical results indicate that the diverging portion of the duct can have a strong reflective effect for partially choked flows.

Kelly, J. J.↗
NASA NTRS1984

Absorptive surfaces of extended reaction angle of incidence considerations

The acoustic properties of a porous absorbing surface are characterized to apply the concepts to practical situations. Propagation constants, impedance, incident pressure wave, sound waves in the air of the pores, and general acoustic behavior are presented mathematically. The design equations are applicable for highly porous bulk materials. Modified equations are appropriate for bulk liners with stiff frames or flexible frames of finite depth.

Lambert, R. F.↗
NASA NTRSDate not supplied

Microstructure Controlled Multi-Layer Porous Material Liner Tested On The Advanced Noise Control Fan

A novel concept of multilayer micro structurally controlled noise mitigation porous material was developed and experimentally validated in the laboratory by normal incidence impedance test. Extensive parametric studies were made to understand various parameters that influence acoustic absorption and transmission loss based on the test specimen size, particle size, porosity, pore size, and its distribution through the thickness. The results were reported in many publications. This work was focused on applying the concept and assessing the validity of the technology to aircraft turbomachine engines. The NASA Glenn Research Center’s Advanced Noise Control Fan (ANCF) low-speed test rig was selected. The liner insert required a 4-ft internal diameter cylinder with a 2-inch thick and 9-inch axial length. The liner was fabricated in eight segments and assembled in an aluminum test rig. The liner was tested for both tonal and broadband noise at the Notre Dame Turbomachinery Lab White Field test facility, where the ANCF is located. The study concludes that: Microstructurally controlled porous material is very effective in dissipating the sound energy; the liner is effective for tonal noise (2 to 13 dB reduction in noise levels) that constitutes the major part of the overall fan noise, especially the blade passing frequency which is generally the dominating component; Also, the liner is effective for broadband noise with reductions in sound pressure level of about 3 dB for the shaft order greater than 20. The proposed two-layer liner model demonstrated the validity of the concept. More studies are required to optimize the design.

Liner↗
NASA NTRS1982

Propagation of spinning acoustic modes in partially choked converging ducts

A computer model based on the wave-envelope technique is used to study the propagation of spinning acoustic modes in converging hard-walled and lined circular ducts carrying near sonic mean flows. The results show that with increasing spinning mode number the intensification of the acoustic signal at the throat decreases for upstream propagation. The influence of the throat Mach number, frequency, boundary-layer thickness, and liner admittance on the propagation of spinning modes is considered.

Nayfeh, A. H.↗
NASA NTRS1986

Advanced high temperature static strain sensor development

An examination was made into various techniques to be used to measure static strain in gas turbine liners at temperatures up to 1150 K (1600 F). The methods evaluated included thin film and wire resistive devices, optical fibers, surface acoustic waves, the laser speckle technique with a heterodyne readout, optical surface image and reflective approaches and capacitive devices. A preliminary experimental program to develop a thin film capacitive device was dropped because calculations showed that it would be too sensitive to thermal gradients. In a final evaluation program, the laser speckle technique appeared to work well up to 1150 K when it was used through a relatively stagnant air path. The surface guided acoustic wave approach appeared to be interesting but to require too much development effort for the funds available. Efforts to develop a FeCrAl resistive strain gage system were only partially successful and this part of the effort was finally reduced to a characterization study of the properties of the 25 micron diameter FeCrAl (Kanthal A-1) wire. It was concluded that this particular alloy was not suitable for use as the resistive element in a strain gage above about 1000 K.

Hulse, C. O.↗
NASA NTRS1997

TBIEM3D: A Computer Program for Predicting Ducted Fan Engine Noise

This document describes the usage of the ducted fan noise prediction program TBIEM3D (Thin duct - Boundary Integral Equation Method - 3 Dimensional). A scattering approach is adopted in which the acoustic pressure field is split into known incident and unknown scattered parts. The scattering of fan-generated noise by a finite length circular cylinder in a uniform flow field is considered. The fan noise is modeled by a collection of spinning point thrust dipoles. The program, based on a Boundary Integral Equation Method (BIEM), calculates circumferential modal coefficients of the acoustic pressure at user-specified field locations. The duct interior can be of the hard wall type or lined. The duct liner is axisymmetric, locally reactive, and can be uniform or axially segmented. TBIEM3D is written in the FORTRAN programming language. Input to TBIEM3D is minimal and consists of geometric and kinematic parameters. Discretization and numerical parameters are determined automatically by the code. Several examples are presented to demonstrate TBIEM3D capabilities.

Dunn, M. H.↗
NASA NTRS2005

Gen 2.0 Mixer/Ejector Nozzle Test at LSAF June 1995 to July 1996

Testing of the HSCT Generation 2.0 nozzle model hardware was conducted at the Boeing Low Speed Aeroacoustic Facility, LSAF. Concurrent measurements of noise and thrust were made at critical takeoff design conditions for a variety of mixer/ejector model hardware. Design variables such as suppressor area ratio, mixer area ratio, liner type and thickness, ejector length, lobe penetration, and mixer chute shape were tested. Parallel testing was conducted at G.E.'s Cell 41 acoustic free jet facility to augment the LSAF test. The results from the Gen 2.0 testing are being used to help shape the current nozzle baseline configuration and guide the efforts in the upcoming Generation 2.5 and 3.0 nozzle tests. The Gen 2.0 results have been included in the total airplane system studies conducted at MDC and Boeing to provide updated noise and thrust performance estimates.

Arney, L. D.↗
NASA NTRS2017

Evaluation of Spanwise Variable Impedance Liners with Three-Dimensional Aeroacoustics Propagation Codes

Three perforate-over-honeycomb liner configurations, one uniform and two with spanwise variable impedance, are evaluated based on tests conducted in the NASA Grazing Flow Impedance Tube (GFIT) with a plane-wave source. Although the GFIT is only 2" wide, spanwise impedance variability clearly affects the measured acoustic pressure field, such that three-dimensional (3D) propagation codes are required to properly predict this acoustic pressure field. Three 3D propagation codes (CHE3D, COMSOL, and CDL) are used to predict the sound pressure level and phase at eighty-seven microphones flush-mounted in the GFIT (distributed along all four walls). The CHE3D and COMSOL codes compare favorably with the measured data, regardless of whether an exit acoustic pressure or anechoic boundary condition is employed. Except for those frequencies where the attenuation is large, the CDL code also provides acceptable estimates of the measured acoustic pressure profile. The CHE3D and COMSOL predictions diverge slightly from the measured data for frequencies away from resonance, where the attenuation is noticeably reduced, particularly when an exit acoustic pressure boundary condition is used. For these conditions, the CDL code actually provides slightly more favorable comparison with the measured data. Overall, the comparisons of predicted and measured data suggest that any of these codes can be used to understand data trends associated with spanwise variable-impedance liners.

Jones, M. G.↗
NASA NTRS1988

Detection of bondline delaminations in multilayer structures with lossy components

The detection of bondline delaminations in multilayer structures using ultrasonic reflection techniques is a generic problem in adhesively bonded composite structures such as the Space Shuttles's Solid Rocket Motors (SRM). Standard pulse echo ultrasonic techniques do not perform well for a composite resonator composed of a resonant layer combined with attenuating layers. Excessive ringing in the resonant layer tends to mask internal echoes emanating from the attenuating layers. The SRM is made up of a resonant steel layer backed by layers of adhesive, rubber, liner and fuel, which are ultrasonically attenuating. The structure's response is modeled as a lossy ultrasonic transmission line. The model predicts that the acoustic response of the system is sensitive to delaminations at the interior bondlines in a few narrow frequency bands. These predictions are verified by measurements on a fabricated system. Successful imaging of internal delaminations is sensitive to proper selection of the interrogating frequency. Images of fabricated bondline delaminations are presented based on these studies.

Madaras, Eric I.↗
DOE OSTI2020

Development and Validation of Quantitative Model-Based Image Reconstruction for NDE of Reinforced Steel-Lined Concrete Structures: Kal-El FY 2020

This project studied the capabilities of Model-Based Image Reconstruction (MBIR) and Machine Learning (ML) algorithms in the imaging and estimation of rebar corrosion from ultrasound signals. The application was challenging due to the introduction of a steel liner between the sensor and the concrete containing the rebar. The study focused in a synthetic specimen with a 6.35 mm thick steel liner, and a 19.05 mm diameter rebar at a depth of 44.5 mm and with four levels of corrosion; 0%, 20%, 50%, and 100% corrosion level. The corrosion was applied uniformly around the rebar, generating a ring in the perimeter of the rebar with different acoustic density. In order to generate a realistic synthetic dataset, we added random texture to the concrete of the synthetic specimens. This texture will mimic the variations encountered in real concrete specimens.We adapted our MBIR algorithm for the application and enhanced the algorithm to integrate in the physical model known specimen features, such as the steel liner thickness. The new MBIR method was able to cancel out reverberation from the steel liner and properly image the rebar. In particular, corrosion for the 50% and 100% cases were easily visible and quantitative metrics showed a slight separation for the 0% and 20% levels. The quantitative results were in agreement with the qualitative assessment. We also developed a ML XGBoost model to estimate corrosion level from the ultrasound signals. By combining the ML method with MBIR, we can pinpoint in the ultrasound signals the section that corresponds to the echoes from the rebar. The extract signals are processed by the XGBoost model for prediction. From each system scan, we obtain 15 predictions. The median prediction value is used as the final prediction. The True Acceptance Rate for the method is over 99%.

36 MATERIALS SCIENCE↗
NASA NTRS2017

Evaluating the Acoustic Benefits of Over-the-Rotor Acoustic Treatments Installed on the Advanced Noise Control Fan

Over the last 15 years, over-the-rotor acoustic treatments have been evaluated by NASA with varying success. Recently, NASA has been developing the next generation of over-the-rotor acoustic treatments for fan noise reduction. The NASA Glenn Research Centers Advanced Noise Control Fan was used as a Low Technology Readiness Level test bed. A rapid prototyped in-duct array consisting of 50 microphones was employed, and used to correlate the in-duct analysis to the far-field acoustic levels and to validate an existing beam-former method. The goal of this testing was to improve the Technology Readiness Level of various over-the-rotor acoustic treatments by advancing the understanding of the physical mechanisms and projecting the far-field acoustic benefit.

Fan noise↗
NASA NTRSDate not supplied

CST Inlet Treatment Modeling

Modeling of varying liner properties in Actran through the use of the Grazing Flow Impedance Tube (GFIT) geometry.

supersonic, acoustics, inlet↗
NASA NTRS1974

An experimental study of the effect of treated length on fan inlet noise suppressors

The effect of length of acoustic treatment was studied on a full scale fan using two different inlets. Analysis of the data revealed that measured suppression varied linearly with the length of the ringed liner segments as anticipated. Further analysis indicated that the wall only portion of the treatment was substantially more effective than anticipated, suggesting that, if only moderate suppression is needed, wall only treatment may suffice. The two inlets behaved similarly. Introduction of a hard exhaust splitter into the configuration resulted in a noise increase at certain frequencies.

Dittmar, J. H.↗
NASA NTRS2016

A Requirements-Driven Optimization Method for Acoustic Treatment Design

Acoustic treatment designers have long been able to target specific noise sources inside turbofan engines. Facesheet porosity and cavity depth are key design variables of perforate-over-honeycomb liners that determine levels of noise suppression as well as the frequencies at which suppression occurs. Layers of these structures can be combined to create a robust attenuation spectrum that covers a wide range of frequencies. Looking to the future, rapidly-emerging additive manufacturing technologies are enabling new liners with multiple degrees of freedom, and new adaptive liners with variable impedance are showing promise. More than ever, there is greater flexibility and freedom in liner design. Subject to practical considerations, liner design variables may be manipulated to achieve a target attenuation spectrum. But characteristics of the ideal attenuation spectrum can be difficult to know. Many multidisciplinary system effects govern how engine noise sources contribute to community noise. Given a hardwall fan noise source to be suppressed, and using an analytical certification noise model to compute a community noise measure of merit, the optimal attenuation spectrum can be derived using multidisciplinary systems analysis methods. The subject of this paper is an analytical method that derives the ideal target attenuation spectrum that minimizes noise perceived by observers on the ground.

Aircraft Noise↗
NASA NTRS1975

Propagation of Sound at Moderate and High Intensities in Absorbent and Hard-Walled Cylindrical Ducts

The propagation of plane wave and higher order acoustic modes in both hard-walled and absorbent cylindrical ducts was studied at moderate sound intensities where the linear wave equation is valid, and at high intensities where nonlinear effects can be observed. The experiments were conducted with an anechoically terminated twelve-inch inside-diameter transite pipe. Various types of sound sources were mounted at one end of the duct to generate the desired acoustic fields within the duct. Arrays of conventional loudspeakers were used to generate plane waves and higher order acoustic modes at moderate intensities, and an array of four high intensity electro-pneumatic sound sources was used for the experiments in the nonlinear region. The attenuation of absorbent liners made of several different materials was obtained at moderate intensities for both plane waves and high order modes. It was found that the characteristics of the liners studied did not change appreciably at high intensities.

Mcdaniel, Oliver Herbert↗
NASA NTRS1989

OTVE combustor wall condition monitoring

Conventional ultrasonics, eddy current, and electromagnetic acoustic transduction (EMAT) technologies were evaluated to determine their capability of measuring wall thickness/wear of individual cooling channels in test specimens simulating conditions in the throat region of an OTVE combustion chamber liner. Quantitative results are presented for the eddy current technology, which was shown to measure up to the optimum 20-mil wall thickness with near single channel resolution. Additional results demonstrate the capability of the conventional ultrasonics and EMAT technologies to detect a thinning or cracked wall. Recommendations for additional eddy current and EMAT development tests are presented.

Szemenyei, Brian↗