Search NASA⌕ Search

SEARCH · Search NASA

Results for “ACOUSTIC SIMULATION”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

Experimental Validation of Numerical Simulations for an Acoustic Liner in Grazing Flow

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 using the Grazing Flow Impedance Tube at the NASA Langley Research Center. In the experiment, a liner is installed in the upper wall of a rectangular flow duct with a 2 inch by 2.5 inch cross section. Spatial distribution of sound pressure levels and relative phases are measured on the wall opposite the liner in the presence of a Mach 0.3 grazing flow. The computer code is validated by comparing computed results with experimental measurements. Good agreements are found. The numerical simulation code is then used to investigate the physical properties of the acoustic liner. It is shown that an acoustic liner can produce self-noise in the presence of a grazing flow and that a feedback acoustic resonance mechanism is responsible for the generation of this liner self-noise. In addition, the same mechanism also creates additional liner drag. An estimate, based on numerical simulation data, indicates that for a resonant liner with a 10% open area ratio, the drag increase would be about 4% of the turbulent boundary layer drag over a flat wall.

Tam, Christopher K. W.↗
NASA NTRS2019

Assessment of Mixer-Ejector Nozzle with Thermal Acoustic Shield for Jet Noise Reduction

A tendency for excessive exhaust jet mixing noise from low bypass ratio turbofan engines is recognized as a key challenge in the design of commercial supersonic aircraft. In this work we investigate a unique combination of two noise mitigation methods as a novel strategy to reduce jet mixing noise. First, a thermal acoustic shield (TAS) is used to reflect high frequency acoustic waves at small angles to the jet axis; second, a mixer-ejector (ME) nozzle is used to mechanically shield noise propagating at large angles to the axis. The ME shroud also provides a convenient location for a TAS nozzle and improves TAS effectiveness by limiting the downstream extent of high frequency noise generation. In an additional benefit for a velocity-matched TAS stream, the ME allows a reduction in strength of the TAS outer shear layer which could serve as a secondary noise source. The present work provides a quantitative assessment of the ME-TAS concept, using a combination of RANS CFD simulations, acoustic analogy calculations for the farfield Green's function, and surrogate-based modeling and parameter space exploration. We first evaluate a subscale configuration, then use scaling arguments to apply subscale results to the systems-level analysis of a flight configuration; the latter configuration includes a generic low bypass ratio turbofan engine with an engine-driven electric generator for supplementary heating of the TAS stream. Additional RANS CFD calculations are performed for a notional ME-TAS geometry based on the full scale configuration, and various modeling assumptions and operational characteristics are evaluated. The ME-TAS concept is shown to provide effective shielding for high frequency jet noise, and should enable comparable noise suppression to a stand-alone ME of considerably greater length, weight and drag. In addition to investigating the integrated ME-TAS system, the present work differs from previous research into TAS and related fluidic shield concepts through the inclusion of modern numerical analysis tools and the systematic numerical examination of various design parameters.

thermal acoustic shield↗
DOE OSTI2016

Effects of non-homogeneous flow on ADCP data processing in a hydroturbine forebay

Observations of the flow conditions in the forebay of a hydroelectric power station indicate significant regions of non-homogeneous velocities near the intakes and shoreline. The effect of these non-homogeneous regions on the velocity measurement of an acoustic Doppler current profiler (ADCP) is investigated. By using a numerical model of an ADCP operating in a velocity field calculated using computational fluid dynamics (CFD), the errors due to the spatial variation of the flow velocity are identified. The numerical model of the ADCP is referred to herein as a Virtual ADCP (VADCP). Two scenarios are modeled in the numerical analyses presented. Firstly the measurement error of the VADCP is calculated for a single instrument adjacent to the short converging intake of the powerhouse. Secondly, the flow discharge through the forebay is estimated from a transect of VADCP instruments at dif- ferent distances from the powerhouse. The influence of instrument location and orientation are investigated for both cases. A velocity error of over up to 94% of the reference velocity is calculated for a VADCP modeled adjacent to an operating intake. Qualitative agreement is observed between the calculated VADCP velocities and reference velocities by an offset of one intake height upstream of the powerhouse.

13 HYDRO ENERGY↗
DOE OSTI2021

Empirical Acoustic Source Model for Chemical Explosions in Air

Chemical explosions generate pressure disturbances in air that radiate as nonlinear shock waves near the source and transition into acoustic waves with distance. Because low-frequency acoustic waves generally travel large distances without significant loss of energy, they are often used for explosion monitoring and yield estimation. However, quantitative relationships between acoustic energy and explosion yields are required for accurate yield estimation. Here, we develop an empirical acoustic source model for chemical explosions from experimental data. The empirical model returns the acoustic pressure waveform for the detonation of 1 kg of trinitrotoluene, which is conventionally used to represent the explosive release of 4.184 MJ of explosion energy. The full-waveform model can be used to predict acoustic signals for an arbitrary yield of a high-explosive detonation based on the standard scaling law and to estimate acoustic energies in a specific frequency range. We evaluate the accuracy of the acoustic source model independently by estimating the yield of other explosive events that are not included in the model development. Finally, statistical characteristics of the model and their implications for the uncertainty quantification of estimated yields are discussed.

58 GEOSCIENCES↗
NASA NTRS1978

A method for determining internal noise criteria based on practical speech communication applied to helicopters

The relationship between the internal noise environment of helicopters and the ability of personnel to understand commands and instructions was studied. A test program was conducted to relate speech intelligibility to a standard measurement called Articulation Index. An acoustical simulator was used to provide noise environments typical of Army helicopters. Speech material (command sentences and phonetically balanced word lists) were presented at several voice levels in each helicopter environment. Recommended helicopter internal noise criteria, based on speech communication, were derived and the effectiveness of hearing protection devices were evaluated.

Sternfeld, H., Jr.↗
NASA NTRS1982

Status and capabilities of the National Full Scale Facility 40- by 80-foot wind tunnel modification

The background, requirements, and aerodynamic design of the modified NASA Ames 40 x 80 ft wind tunnel are reviewed, along with the systems integration and systems test results. Advancing vehicle sizes and airspeeds required a larger wind tunnel test section and a capability for 100 and 300 knots airspeed simulation. Acoustic mufflers at the inlet and exit of the nonreturn circuit provide noise suppression. The enlarged test section is intended to accomodate the complex flowfields of wings with high lift coefficients, and the drive system is designed with minimum residual swirl. Features of the fan blades are examined, along with characteristics of the test channels, control vanes and louvers, the exit, circuit losses, temperature rises during operation of the nonreturn circuit, and the facility acoustics. Specific construction problems and solutions for the conversion process are outlined, and it is noted that operational status is expected at the end of 1982.

Mort, K. W.↗
NASA NTRS1983

Application of optical fibers to wide-band differential interferometry

A broadband differential optical interferometer that uses an optical-fiber waveguide to transmit coherent light to a surface under inspection is discussed. Input laser light is coupled into two single-mode optical fibers in a stationary input optics enclosure. The fibers transmit the light to a small, remote detection head where it is used in a wide-band differential interferometer to detect continuous and pulsed surface-particle displacements. The effective separation between the input optics and the detection head allows simple surface scanning and probe alignment. Detection of simulated acoustic emission pulses by a prototype test unit is reported.

Garg, A. O.↗
NASA NTRS1989

NASA rotorcraft technology for the 21st century

Current and planned rotorcraft technology-related research at NASA's Ames, Lewis, and Langley research centers is discussed with a view to the fruits of these efforts beyond the year 2000. Examples of promising technologies are higher-harmonic and dynamic rotor controls, advanced structural composites, aerodynamics and acoustics simulation models for design predictions, automated flight controls, and high-reliability rotor drivetrains. The overall payoff from an integration of these technologies will allow safe automated flying in all weather conditions, as well as precision-hover and exceptionally low noise and vibration levels.

Albers, James A.↗
NASA NTRS1992

Extensional and flexural waves in a thin-walled graphite/epoxy tube

Simulated acoustic emission signals were induced in a thin-walled graphite/epoxy tube by means of lead breaks (Hsu-Nielsen source). The tube is of similar material and layup to be used by NASA in fabricating the struts of Space Station Freedom. The resulting waveforms were detected by broad band ultrasonic transducers and digitized. Measurements of the velocities of the extensional and flexural modes were made for propagation directions along the tube axis (0 degrees), around the tube circumference (90 degrees) and at an angle of 45 degrees. These velocities were found to be in agreement with classical plate theory.

Prosser, William H.↗
NASA NTRS1991

AE Source Orientation by Plate Wave Analysis

Lead breaks (Hsu-Neilsen source) were used to generate simulated acoustic emission signals in an aluminum plate at angles of 0, 30, 60, and 90 degrees with respect to the plane of the plate. This was accomplished by breaking the lead on slots cut into the plate at the respective angles. The out-of-plane and in-plane displacement components of the resulting signals were detected by broad band transducers and digitized. Analysis of the waveforms showed them to consist of the extensional and flexural plate modes. The amplitude of both components of the two modes was dependent on the source orientation angle. This suggests that plate wave analysis may be used to determine the source orientation of acoustic emission sources.

Gorman, Michael R.↗
NASA NTRS1992

Extensional and Flexural Waves in a Thin-Walled Graphite/Epoxy Tube

Simulated acoustic emission signals were induced in a thin-walled graphite/epoxy tube by means of lead breaks (Hsu-Neilsen source). The tube is of similar material and layup to be used by NASA in fabricating the struts of Space Station Freedom. The resulting waveforms were detected by broad band ultrasonic transducers and digitized. Measurements of the velocities of the extensional and flexural modes were made for propagation directions along the tube axis (0 degrees), around the tube circumference (90 degrees) and at an angle of 45 degrees. These velocities were found to be in agreement with classical plate theory.

Prosser, William H.↗
NASA NTRS2009

Electromagnetic Cavity Effects from Transmitters Inside a Launch Vehicle Fairing

This paper provides insight into the difficult analytical issue for launch vehicles and spacecraft that has applicability outside of the launch industry. Radiation from spacecraft or launch vehicle antennas located within enclosures in the launch vehicle generates an electromagnetic environment that is difficult to accurately predict. This paper discusses the test results of power levels produced by a transmitter within a representative scaled vehicle fairing model and provides preliminary modeling results at the low end of the frequency test range using a commercial tool. Initially, the walls of the fairing are aluminum and later, layered with materials to simulate acoustic blanketing structures that are typical in payload fairings. The effects of these blanketing materials on the power levels within the fairing are examined.

Trout, Dawn↗
NASA NTRS2009

Electromagnetic Cavity Effects from Transmitters Inside a Launch Vehicle Fairing

This paper provides insight into the difficult analytical issue for launch vehicles and spacecraft that has applicability outside of the launch industry. Radiation from spacecraft or launch vehicle antennas located within enclosures in the launch vehicle generates an electromagnetic environment that is difficult to accurately predict. This paper discusses the test results of power levels produced by a transmitter within a representative scaled vehicle fairing model and provides preliminary modeling results at the low end of the frequency test range using a commercial tool. Initially, the walls of the fairing are aluminum and later, layered with materials to simulate acoustic blanketing structures that are typical in payload fairings. The effects of these blanketing materials on the power levels within the fairing are examined.

Trout, Dawn H.↗
NASA NTRS2019

Jet Noise Prediction for Low Boom Aircraft

Enabling jet acoustics simulations on full scale flight vehicles utilizing zonal hybrid RANS/LES within the Launch Ascent and Vehicle Aerodynamics (LAVA) Solver. Hybrid RANS/LES technology will assist in the development for innovative concepts for integrated supersonic propulsion systems. Modeling and simulation practices must be scrutinized further and new methods need to be developed.

Stich, Gerrit↗
NASA NTRS2016

Wavenumber-frequency deconvolution of aeroacoustic microphone phased array data of arbitrary coherence

Deconvolution of aeroacoustic data acquired with microphone phased arrays is a computationally-challenging task for distributed sources with arbitrary coherence. A new technique for performing such deconvolution is proposed. This technique relies on analysis of the array data in the wavenumber-frequency domain, allowing for fast convolution and reduced storage requirements when compared to traditional coherent deconvolution. A positive semidefinite constraint for the iterative deconvolution procedure is implemented and shows improved behavior in terms of quantifiable convergence metrics when compared to a standalone covariance inequality constraint. A series of simulations validates the method's ability to resolve coherence and phase angle relationships between partially-coherent sources, as well as determines convergence criteria for deconvolution analysis. Simulations for point sources near the microphone phased array show potential for handling such data in the wavenumber-frequency domain. In particular, a physics-based integration boundary calculation is described, and can successfully isolate sources and track the appropriate integration bounds with and without the presence of flow. Magnitude and phase relationships between multiple sources are successfully extracted. Limitations of the deconvolution technique are determined from the simulations, particularly in the context of a simulated acoustic field in a closed test section wind tunnel with strong boundary layer contamination. A final application to a trailing edge noise experiment conducted in an open-jet wind tunnel matches best estimates of acoustic levels from traditional calculation methods and qualitatively assesses the coherence characteristics of the trailing edge noise source.

phased array↗
NASA NTRS2016

Using Simulation to Analyze Acoustic Environments

One of the main projects that was worked on this semester was creating an acoustic model for the Advanced Space Suit in Comsol Multiphysics. The geometry tools built into the software were used to create an accurate model of the helmet and upper torso of the suit. After running the simulation, plots of the sound pressure level within the suit were produced, as seen below in Figure 1. These plots show significant nulls which should be avoided when placing microphones inside the suit. In the future, this model can be easily adapted to changes in the suit design to determine optimal microphone placements and other acoustic properties. Another major project was creating an acoustic diverter that will potentially be used to route audio into the Space Station's Node 1. The concept of the project was to create geometry to divert sound from a neighboring module, the US Lab, into Node 1. By doing this, no new audio equipment would need to be installed in Node 1. After creating an initial design for the diverter, analysis was performed in Comsol in order to determine how changes in geometry would affect acoustic performance, as shown in Figure 2. These results were used to produce a physical prototype diverter on a 3D printer. With the physical prototype, testing was conducted in an anechoic chamber to determine the true effectiveness of the design, as seen in Figure 3. The results from this testing have been compared to the Comsol simulation results to analyze how closely the Comsol results are to real-world performance. While the Comsol results do not seem to closely resemble the real world performance, this testing has provided valuable insight into how much trust can be placed in the results of Comsol simulations. A final project that was worked on during this tour was the Audio Interface Unit (AIU) design for the Orion program. The AIU is a small device that will be used for as an audio communication device both during launch and on-orbit. The unit will have functions including push-to-talk buttons and volume control. With this project, an existing design was modified based on prior feedback that had been received. With the modified design, I created a 3D printed prototype, shown in Figure 4, which was then used in suited evaluations performed by crew members. The feedback received from those evaluations will be utilized to help create the best possible Orion AIU. As a whole, a number of different interesting engineering projects were worked on over the course of this semester. For many of these projects, acoustic simulations provided valuable insight into how different environments would respond to sound. While work is still underway to verify the results of these simulations, the results are fascinating because of the interesting ways that sound waves interact with the environment. Going forward, it will be interesting to see how closely these results can be matched by real-world test data.

Wood, Eric J.↗