Early Detection of Active Region Emergence in the Solar Interior Using Acoustic Power Maps and Machine Learning Data Analysis
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Acoustic Measurements from Wind Tunnel Test of AMELIA - Advanced Model for Extreme Lift and Improved Aeroacoustics
A wind tunnel test has been conducted to measure the aerodynamic and acoustic performance of an active circulation-control aircraft with leading- and trailing- edge slot blowing. The 11 Advanced Model for Extreme Lift and Improved Aeroacoustics (AMELIA) model was tested in the Arnold Engineering Development Center (AEDC) National Full Scale Aerodynamics Complex (NFAC) 40- by 80-Ft wind tunnel. Forward velocities ranged from 0 to Mach 0.15 and total slot mass-flow was varied from 0 to 2.8 lbmsec. Angle-of-attack and sideslip ranges were -5 to 25 and -10 to 10, respectively.This reports summarizes acoustic measurements from the wind tunnel test and the corrections applied to the released acoustic data. The analysis focuses on measurements for the clean wing configuration (turbine propulsion simulators removed) with trailing-and leading-edge slot blowing and with trailing-edge blowing, for systematic variations in slot mass flow from nearly zero to the system maximum. The acoustic measurements from a fixed phased microphone array and seven fixed microphones were corrected for sensor directional response and atmospheric attenuation. Graphs of 13-octave spectra, narrowband spectra, and directional variations in OASPL are presented for each active lift configuration. This report is intended to document the corresponding set of corrected data that is now available for development and verification of new predictive models of the active lift source.For large slot mass flow conditions 13-octave spectral shapes were level and flat, typical of a pink noise source. Little source directivity was present in the OASPL levels for the 0 flap conditions and show only a slight downstream increase with the 60 flap configuration. For moderate to high slot mass flow conditions trailing-edge only blowing spectra were similar to leading- and trailing edge blowing cases. However for the lower mass flows variations of as much as 5 dB were observed.
CCW↗
Structure and propagation of supersonic singularities from helicoidal sources
An asymptotic analysis of the acoustic field radiated by a supersonic helicoidal line source distribution is given. The asymptotic results are valid in the vicinity of the Mach surfaces associated with the moving sources. Particular attention is paid to the singular nature of the field on the Mach surfaces, which the analysis describes exactly. In addition, it is found that the asymptotic approximation predicts numerical values of the pressure with considerable accuracy. Some details on the field of a single source are derived as a special case.
Myers, M. K.↗
Thermal Electron Contributions to Current-Driven Instabilities: SCIFER Observations in the 1400-km Cleft Ion Fountain and Their Implications to Thermal Ion Energization
SCIFER TECHS observations of the variations in the thermal electron distribution in the 1400-km altitude cleft are associated with periods of intense ion heating and field-aligned currents. Energization of the thermal ion plasma in the mid-altitude cleft occurs within density cavities accompanied by enhanced thermal electron temperatures, large field-aligned thermal electron plasma flows and broadband low-frequency electric fields. Variations in the thermal electron contribution to field-aligned current densities indicate small scale (approximately 100's m) filamentary structure embedded within the ion energization periods. TECHS observations of the field-aligned drift velocities and temperatures of the thermal electron distribution are presented to evaluate the critical velocity thresholds necessary for the generation of electrostatic ion cyclotron and ion acoustic instabilities. This analysis suggests that, during periods of thermal ion energization, sufficient drift exists in the thermal electron distribution to excite the electrostatic ion cyclotron instability. In addition, brief periods exist within the same interval where the drift of the thermal electron distribution is sufficient to marginally excite the ion acoustic instability. In addition, the presence an enhancement in Langmuir emission at the plasma frequency at the center of the ion energization region, accompanied by the emission's second-harmonic, and collocated with observations of high-frequency electric field solitary structures suggest the presence of electron beam driven decay of Langmuir waves to ion acoustic modes as an additional free energy source for ion energization.
Adrian, Mark L.↗
Acoustic Testing of a High-Tip-Speed Fan with Bypass-Duct Liners
Under a pair of Space Act Agreements between NASA and Honeywell Aerospace, a model-scale (22 in.-diameter fan) acoustic wind tunnel test was carried out in the fall of 2014 in the NASA Glenn Research Center 9- by 15-Foot Low-Speed Wind Tunnel. The goal was to obtain acoustic pressure measurements for far-field, inlet and exit rotating rake, and in-duct microphone locations. This supersonic-tip-speed fan was tested in three bypass duct configurations: hard-wall, traditional liner, and advanced multiple-degree-of-freedom. Limited aerodynamic data was collected to verify the expected operating conditions. Preliminary analysis of the acoustic data finds it suitable for use in evaluating current NASA and Honeywell Aerospace acoustic tools and liner design practices.
Noise↗
Acoustic Testing of a High-Tip-Speed Fan with Bypass-Duct Liners - Overview
Under a pair of Space Act Agreements between NASA and Honeywell Aerospace, a model-scale (22 in.-diameter fan) acoustic wind tunnel test was carried out in the fall of 2014 in the NASA Glenn Research Center 9- by 15-Foot Low-Speed Wind Tunnel. The goal was to obtain acoustic pressure measurements for far-field, inlet and exit rotating rake, and in-duct microphone locations. This supersonic-tip-speed fan was tested in three bypass duct configurations: hard-wall, traditional liner, and advanced multiple-degree-of-freedom. Limited aerodynamic data was collected to verify the expected operating conditions. Preliminary analysis of the acoustic data finds it suitable for use in evaluating current NASA and Honeywell Aerospace acoustic tools and liner design practices. This report provides an overview of the test and some preliminary findings.
Miller, Christopher J.↗
Analysis of Particle Image Velocimetry (PIV) Data for Acoustic Velocity Measurements
Acoustic velocity measurements were taken using Particle Image Velocimetry (PIV) in a Normal Incidence Tube configuration at various frequency, phase, and amplitude levels. This report presents the results of the PIV analysis and data reduction portions of the test and details the processing that was done. Estimates of lower measurement sensitivity levels were determined based on PIV image quality, correlation, and noise level parameters used in the test. Comparison of measurements with linear acoustic theory are presented. The onset of nonlinear, harmonic frequency acoustic levels were also studied for various decibel and frequency levels ranging from 90 to 132 dB and 500 to 3000 Hz, respectively.
Blackshire, James L.↗
Acoustic levitation in the presence of gravity
The method of Gor'kov (1961) has been applied to derive general expressions for the total potential and force on a small spherical object in a resonant chamber in the presence of both acoustic and gravitational force fields. The levitation position is also determined in rectangular resonators for the simultaneous excitation of up to three acoustic modes, and the results are applied to the triple-axis acoustic levitator. The analysis is applied to rectangular, spherical, and cylindrical single-mode levitators that are arbitrarily oriented relative to the gravitational force field. Criteria are determined for isotropic force fields in rectangular and cylindrical resonators. It is demonstrated that an object will be situated within a volume of possible levitation positions at a point determined by the relative strength of the acoustic and gravitational fields and the orientation of the chamber relative to gravity.
Collas, P.↗
Non-linear wave propagation in acoustically lined circular ducts
An analysis is presented of the nonlinear effects of the gas motion as well as of the acoustic lining material on the transmission and attenuation of sound in a circular duct with a uniform cross-section and no mean flow. The acoustic material is characterized by an empirical, nonlinear impedance in which the instantaneous resistance is a nonlinear function of both the frequency and the acoustic velocity. The results show that there exist frequency bandwidths around the resonant frequencies in which the nonlinearity decreases the attenuation rate, and outside which the nonlinearity increases the attenuation rate, in qualitative agreement with experimental observations. Moreover, the effect of the gas nonlinearity increases with increasing sound frequency, whereas the effect of the material nonlinearity decreases with increasing sound frequency.
Nayfeh, A. H.↗
General aviation aircraft interior noise problem: Some suggested solutions
Laboratory investigation of sound transmission through panels and the use of modern data analysis techniques applied to actual aircraft is used to determine methods to reduce general aviation interior noise. The experimental noise reduction characteristics of stiffened flat and curved panels with damping treatment are discussed. The experimental results of double-wall panels used in the general aviation industry are given. The effects of skin panel material, fiberglass insulation and trim panel material on the noise reduction characteristics of double-wall panels are investigated. With few modifications, the classical sound transmission theory can be used to design the interior noise control treatment of aircraft. Acoustic intensity and analysis procedures are included.
Roskam, J.↗
Acoustic Noise Prediction of the Amine Swingbed ISS ExPRESS Rack Payload
Acoustics plays a vital role in maintaining the health, safety, and comfort of crew members aboard the International Space Station (ISS). In order to maintain this livable and workable environment, acoustic requirements have been established to ensure that ISS hardware and payload developers account for the acoustic emissions of their equipment and develop acoustic mitigations as necessary. These requirements are verified by an acoustic emissions test of the integrated hardware. The Amine Swingbed ExPRESS (Expedite the PRocessing of ExperimentS to Space) rack payload creates a unique challenge to the developers in that the payload hardware is transported to the ISS in phases, making an acoustic emissions test on the integrated flight hardware impossible. In addition, the payload incorporates a high back pressure fan and a diaphragm vacuum pump, which are recognized as significant and complex noise sources. In order to accurately predict the acoustic emissions of the integrated payload, the individual acoustic noise sources and paths are first characterized. These characterizations are conducted though a series of acoustic emissions tests on the individual payload components. Secondly, the individual acoustic noise sources and paths are incorporated into a virtual model of the integrated hardware. The virtual model is constructed with the use of hybrid method utilizing the Finite Element Acoustic (FEA) and Statistical Energy Analysis (SEA) techniques, which predict the overall acoustic emissions. Finally, the acoustic model is validated though an acoustic characterization test performed on an acoustically similar mock-up of the flight unit. The results of the validated acoustic model are then used to assess the acoustic emissions of the flight unit and define further acoustic mitigation efforts.
Welsh, David↗
Impact of Future Low-Emissions Combustor Technology on Acoustic Scaling Laws
The work is a summary and further analysis of unlimited-rights acoustic data acquired under NRA Contract NNC16CA39C (September 2016 - November2019) with United Technologies (now Raytheon Technologies) Research Center, East Hartford, Connecticut. NASA/CR-20205011099/VOL1, https://ntrs.nasa.gov/citations/20205011099. The overall goal of the Contract was to develop a first-of-its- kind database of detailed unsteady measurements characterizing noise sources of far-term advanced low-emissions aero-combustors. The program addressed the need for fundamental combustion-noise experiments which, in the near term, enable improvements to reduced-order models for use in system level noise assessments at the preliminary design stage for advanced air transport vehicles. In addition, optical measurement techniques were refined and validated for usage at the higher pressures and temperatures relevant to future combustor designs. In the long term, results from this program can be utilized to validate high-fidelity prediction methods suited for detailed multi-disciplinary acoustics/emissions combustor design. This presentation concentrates on one aspect of the overall project, namely an examination of the legacy scaling laws for broadband combustor noise.
aeroacoustics, turbomachinery noise, combustor noi↗
Spectral analysis, digital integration, and measurement of low backscatter in coherent laser radar
A method of surface acoustic wave (SAW) spectral analysis and digital integration that has been used previously in coherent CW laser work with CO2 lasers at 10.6 microns is described. Expressions are derived for the signal to noise ratio in the measured voltage spectrum with an approximation for the general case and rigorous treatment for the low signal case. The atmospheric backscatter data accumulated by the airborne LATAS (laser true airspeed) coherent laser radar system are analyzed.
Vaughan, J. M.↗
Aeroacoustic Computations of a Transonic Truss-Braced Wing Aircraft: Part 2 – Acoustic Signature and Noise Source Identification
High-fidelity, time-dependent simulations of a Boeing-designed, transonic, truss-braced-wing aircraft in cruise (clean) and landing configurations are leveraged to generate synthetic microphone-phased-array data for airframe noise prediction and assessment. These data sets are used to compute source localization (beamform) maps to determine the location and strength of primary and secondary airframe noise sources associated with this unique configuration. The synthetic phased-array implementation mimics the setup of a flight test. As this study is ongoing, preliminary integrated far-field spectra for the cruise configuration obtained at multiple spatial resolutions revealed significant tonal content that lacked convergence with increased resolution. The origin of several of these tones and their unusual convergence behavior was traced to the larger-than-normal trailing-edge thickness of the “as-tested” cruise model being simulated. Reducing the trailing-edge thickness to more realistic values eliminated most of the tones at low to moderate frequencies and improved spectrum convergence significantly. Applying lessons learned from the cruise simulations, several modifications to the geometry of the landing configuration were made and are described in this work. Results from permeable and solid Ffowcs-Williams and Hawkings surfaces at two different spatial resolutions (coarse and medium) are used to illustrate the major noise sources and determine convergence of the CLEAN integrated noise levels for the entire aircraft as well as major subcomponents. We demonstrate that the low-frequency content of the far-field spectrum is dominated by noise generated from the main landing gear, while the medium- and high-frequency content is dominated by the wing-leading-edge Krueger flaps. Since analysis of the acoustic maps for the landing configuration revealed several clusters of multiple sources along the wing leading edge, “high resolution” processing of the array data was used to distinguish more accurately the locations of sources.
Transonic Truss-Braced Wing↗
Computer programs perform spectral analyses of up to seven time series
Computer programs perform statistical spectral analyses of up to seven time series. These programs should have applicability to a variety of engineering systems in the fields of geophysics, physiology, acoustics, and structural analysis.
Byars, B. J.↗
Monitoring subcritical crack growth by an acoustic technique.
Acoustic Stress Wave Analysis Technique /SWAT/ for monitoring fatigue crack growth by elastic wave propagation detection
Crimmins, P. P.↗
Computational methods for nonlinear acoustic absorbers
Nonlinear acoustic absorbers behavior analysis, discussing spectral and temporal computation methods
Zorumski, W. E.↗
Time-dependent transonic flow solutions for axial turbomachinery
Three-dimensional unsteady transonic flow through an axial turbomachine stage is described in terms of a pair of two-dimensional formulations pertaining to orthogonal surfaces, namely, a blade-to-blade surface and a hub-to-casing surface. The resulting systems of nonlinear, inviscid, compressible equations of motion are solved by an explicit finite-difference technique. The blade-to-blade program includes the periodic interaction between rotor and stator blade rows. Treatment of the boundary conditions and of the blade slipstream motion by a characteristic type procedure is discussed in detail. Harmonic analysis of the acoustic far field produced by the blade row interaction, including an arbitrary initial transient, is outlined. Results from the blade-to-blade program are compared with experimental measurements of the rotating pressure field at the tip of a high-speed fan. The hub-to-casing program determines circumferentially averaged flow properties on a meridional plane. Blade row interactions are neglected in this formulation, but the force distributions over the entire blade surface for both the rotor and stator are obtained. Results from the hub-to-casing program are compared with a relaxation method solution for a subsonic rotor. Results are also presented for a quiet fan stage which includes transonic flow in both the rotor and stator and a normal shock in the stator.
Erdos, J.↗