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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

On the tones and pressure oscillations induced by flow over rectangular cavities

Experimental measurements of the frequencies of discrete tones induced by flow over rectangular cavities were carried out over a range of low subsonic Mach numbers to provide a reliable data base for (aircraft wheel well) cavity noise consideration. A mathematical model of the cavity tones and pressure oscillation phenomenon based on the coupling between shear layer instabilities and acoustic feedback is developed to help in understanding the tone generation mechanism. Good agreement is found between discrete tone frequencies predicted by the model and experimental measurements over a wide range of Mach numbers. Evidence of tones generated by the cavity normal mode resonance mechanism at very low subsonic Mach numbers is also presented.

Tam, C. K. W.↗
NASA NTRS1983

An experimental study of supersonic jet shock-associated noise

A new method of screech tone reduction in underexpanded supersonic jets is utilized to determine if the amplitude of screech is related to the level of shock-associated broadband noise. Acoustic measurements show that as the screech tone is reduced, the broadband shock-associated noise may be increased by up to 4dB at some locations. Several experiments were conducted with disturbances put into the flow upstream of the final contraction. Results from these tests support the concept of linkage between the broadband shock noise and screech tones. Some interesting preliminary results were obtained with a disturbance of the flow at several locations downstream of the nozzle. These results are also discussed.

Nagel, R. T.↗
NASA NTRS2000

A Comparison of Measured Tone Modes for Two Low Noise Propulsion Fans

The acoustic modes for two low tip speed propulsion fans were measured to examine the effects of fan tip speed, at constant pressure ratio. A continuously rotating microphone method was used that provided the complete modal structure (circumferential and radial order) at the fundamental and second harmonic of the blade passing tone as well as most of the third harmonic modes. The fans are compared in terms of their rotor/stator interaction modal power, and total tone power. It was hoped that the lower tip speed might produce less noise. This was not the case. The higher tip speed fan, at both takeoff and cutback speeds, had lower tone and interaction levels. This could be an indication that the higher aerodynamic loading required to produce the same pressure ratio for the lower tip speed fan resulted in a greater velocity deficit in the blade wakes and thus more noise. Results consistent with expected rotor transmission effects were noted in the inlet modal structures of both fans.

Heidelberg, Laurence J.↗
NASA NTRS1987

Acoustic radiation stress measurement

Ultrasonic radio frequency tone-bursts are launched into a sample of material tested. The amplitude of the tone-bursts and the slope of the resulting static displacement pulses are measured. These measurements are used to calculate the nonlinearities of the materials.

Cantrell, John H., Jr.↗
NASA NTRS1996

RSRM Chamber Pressure Oscillations: Transit Time Models and Unsteady CFD

Space Shuttle solid rocket motor low frequency internal pressure oscillations have been observed since early testing. The same type of oscillations also are present in the redesigned solid rocket motor (RSRM). The oscillations, which occur during RSRM burn, are predominantly at the first three motor cavity longitudinal acoustic mode frequencies. Broadband flow and combustion noise provide the energy to excite these modes at low levels throughout motor burn, however, at certain times during burn the fluctuating pressure amplitude increases significantly. The increased fluctuations at these times suggests an additional excitation mechanism. The RSRM has inhibitors on the propellant forward facing surface of each motor segment. The inhibitors are in a slot at the segment field joints to prevent burning at that surface. The aft facing segment surface at a field joint slot burns and forms a cavity of time varying size. Initially the inhibitor is recessed in the field joint cavity. As propellant burns away the inhibitor begins to protrude into the bore flow. Two mechanisms (transit time models) that are considered potential pressure oscillation excitations are cavity-edge tones, and inhibitor hole-tones. Estimates of frequency variation with time of longitudinal acoustic modes, cavity edge-tones, and hole-tones compare favorably with frequencies measured during motor hot firing. It is believed that the highest oscillation amplitudes occur when vortex shedding frequencies coincide with motor longitudinal acoustic modes. A time accurate computational fluid dynamic (CFD) analysis was made to replicate the observations from motor firings and to observe the transit time mechanisms in detail. FDNS is the flow solver used to detail the time varying aspects of the flow. The fluid is approximated as a single-phase ideal gas. The CFD model was an axisymmetric representation of the RSRM at 80 seconds into burn.Deformation of the inhibitors by the internal flow was determined through an iterative structural and CFD analysis. The analysis domain ended just upstream of the nozzle throat. This is an acoustic boundary condition that caused the motor to behave as a closed-open organ pipe. This differs from the RSRM which behaves like a closed-closed organ pipe. The unsteady CFD solution shows RSRM chamber pressure oscillations predominately at the longitudinal acoustic mode frequencies of a closed-open organ pipe. Vortex shedding in the joint cavities and at the inhibitors contribute disturbances to the flow at the second longitudinal acoustic mode frequency. Further studies are planned using an analysis domain that extends downstream of the nozzle throat.

Nesman, Tom↗
DOE OSTI2020

Octet: A coherent qubit control system for trapped-ion quantum computers

This is firmware and software designed for a Zynq UltraScale+ RFSoC chip made by Xilinx, specifically targeted to laser-based individual addressing of trapped ion qubits via a multi-channel AOM. The design features 8 dual-tone outputs with frequencies up to 409 MHz that can be controlled statically or dynamically via on-chip cubic spline interpolation engines that allow one to generate sequences of output waveforms with fast modulation of frequency, phase, amplitude, and z-rotations that are smooth/discrete and can run simultaneously across all parameters/tones. It also features global phase alignment on all tones regardless of frequency and the ability to return to a known phase/frequency at any later time on a per-tone basis without the need for manual bookkeeping. Acoustic and optical cross-talk can also be destructively canceled by adding neighboring outputs with variable amplitude/phase/delay. Each tone can be optionally frequency locked to an external RF source. SAND2020-12703 M Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Lobser, Daniel↗
NASA NTRS1980

Refraction and scattering of sound by a shear layer

The angle and amplitude changes for acoustic waves refracted by a circular open jet shear layer were determined. The generalized refraction theory was assessed experimentally for on axis and off axis acoustic source locations as source frequency varied from 1 kHz to 10 kHz and free stream Mach number varied from 0.1 to 0.4. Angle and amplitude changes across the shear layer show good agreement with theory. Experiments confirm that the refraction theory is independent of shear layer thickness, acoustic source frequency, and source type. A generalized theory is, thus, available for correcting far field noise data acquired in open jet test facilities. The effect of discrete tone scattering by the open jet turbulent shear layer was also studied. Scattering effects were investigated over the same Mach number range as frequency varied from 5 kHz to 15 kHz. Attenuation of discrete tone amplitude and tone broadening were measured as a function of acoustic source position and radiation angle. Scattering was found to be stronger at angles close to the open jet axis than at 90 deg, and becomes stronger as the acoustic source position shifts downstream. A scattering analysis provided an estimate of the onset of discrete tone scattering.

Schlinker, R. H.↗
NASA NTRS1976

Acoustic and aerodynamic performance of a 1.83-meter (6-ft) diameter 1.25-pressure-ratio fan (QF-8)

A 1.25-pressure-ratio 1.83-meter (6-ft) tip diameter experimental fan stage with characteristics suitable for engine application on STOL aircraft was tested for acoustic and aerodynamic performance. The design incorporated proven features for low noise, including absence of inlet guide vanes, low rotor blade tip speed, low aerodynamic blade loading, and long axial spacing between the rotor and stator blade rows. The fan was operated with five exhaust nozzle areas. The stage noise levels generally increased with a decrease in nozzle area. Separation of the acoustic one-third octave results into broadband and pure-tone components showed the broadband noise to be greater than the corresponding pure-tone components. The sideline perceived noise was highest in the rear quadrants. The acoustic results of QF-8 were compared with those of two similar STOL application fans in the test series. The QF-8 had somewhat higher relative noise levels than those of the other two fans. The aerodynamic results of QF-8 and the other two fans were compared with corresponding results from 50.8-cm (20-in.) diam scale models of these fans and design values. Although the results for the full-scale and scale models of the other two fans were in reasonable agreement for each design, the full-scale fan QF-8 results showed poor performance compared with corresponding model results and design expectations. Facility effects of the full-scale fan QF-8 installation were considered in analyzing this discrepancy.

Woodward, R. P.↗
NASA NTRS1994

Active Control of Fan Noise-Feasibility Study: Flyover System Noise Studies - Volume 1

A study has been completed to examine the potential reduction of aircraft flyover noise by the method of active noise control (ANC). It is assumed that the ANC system will be designed such that it cancels discrete tones radiating from the engine fan inlet or fan exhaust duct. Thus, without considering the engineering details of the ANC system design, tone levels are arbitrarily removed from the engine component noise spectrum and the flyover noise EPNL levels are compared with and without the presence of tones. The study was conducted for a range of engine cycles, corresponding to fan pressure ratios from 1.3 to 1.75. The major conclusions that can be drawn are that, for a fan pressure ratio of 1.75, ANC of tones gives about the same suppression as acoustic treatment without ANC, and for a fan pressure ratio of 1.45, ANC appears to offer less effectiveness than passive treatment. Additionally, ANC appears to be more effective at sideline and cutback conditions than at approach. Overall EPNL suppressions due to tone removal range from about 1 to 3 dB at takeoff engine speeds and from 1 to 5 db at approach speeds. Studies of economic impact of the installation of an ANC system for the four engine cases indicate increases of DOC ranging from 1 to 2 percent, favoring the lower fan pressure ratio engines. Further study is needed to confirm the results by examining additional engine data, particularly at low fan pressure ratios, and studying the details of the current results to obtain a more complete understanding. Further studies should also include determining the effects of combining passive and active treatment.

Kraft, Robert E.↗
DOE OSTI2024

Development and experimental evaluation of an acoustic flow meter prototype for measuring air flow

Here, this study outlines the development and testing of a flow meter prototype specifically designed for use in nuclear reactor environments. The meter uses flow-induced vibration to measure flow rates and is designed for remote monitoring in harsh environments where radiation can damage electronics. The device generates a vibration signal produced by a feedback system when fluid flows out of an orifice and interacts with a downstream wedge. The frequency of the vibration signal corresponds directly to flow rate and velocity. The study investigates geometric parameters intrinsic to the prototype, such as orifice height, width, edge distance, and chamber length. Different configurations were also tested, including a bypass loop with variable cross-sections around the device. The investigation results reveal the impact of these geometric parameters on the vibration signal output, providing valuable insights for future design improvements and enhancing the effectiveness of flow metering systems used in nuclear reactor applications.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS2004

The Effect of Nozzle Trailing Edge Thickness on Jet Noise

The effect of nozzle trailing edge thickness on broadband acoustic radiation and the production of tones is investigated for coannular nozzles. Experiments were performed for a core nozzle trailing edge thickness between 0.38 mm and 3.17 mm. The on-set of discrete tones was found to be predominantly affected by the velocity ratio, the ratio of the fan velocity to the core velocity, although some dependency on trailing edge thickness was also noted. For a core nozzle trailing edge thickness greater than or equal to 0.89 mm, tones were produced for velocity ratios between 0.91 and 1.61. For a constant nozzle trailing edge thickness, the frequency varied almost linearly with the core velocity. The Strouhal number based on the core velocity changed with nozzle trailing edge thickness and varied between 0.16 and 0.2 for the core nozzles used in the experiments. Increases in broadband noise with increasing trailing edge thickness were observed for tone producing and non-tone producing conditions. A variable thickness trailing edge (crenellated) nozzle resulted in no tonal production and a reduction of the broadband trailing edge noise relative to that of the corresponding constant thickness trailing edge.

Henderson, Brenda↗
NASA NTRS2023

Acoustics of a Supersonic Mach 1.4 Axisymmetric Spike Inlet

An inlet for a supersonic commercial aircraft is analyzed for noise radiation in low-speed configuration, with auxiliary inlet open. Duct mode amplitudes generated by the fan are determined by post-processing a URANS simulation and become a boundary condition to the inlet. Far-field sound is modeled using commercial acoustics finite element software. The effect of inlet geometry and acoustic liners is simulated and discussed. Absolute levels for inlet tone noise are predicted.

Supersonics↗
NASA NTRS1983

Supersonic jet screech tone cancellation

A new method of supersonic jet screech tone reduction is presented. The method utilizes a sound reflecting surface positioned upstream of the nozzle exit a distance of one-quarter wavelength of the fundamental screech tone. The reflector establishes a standing wave pattern of acoustic waves with a node at the nozzle exit plane. The pressure minimum at the exit halts the screech tone feedback mechanism. Experimental results indicate that the method eliminates supersonic jet screech as effectively as the currently accepted technique using an intrusive tab, but without distortion of the jet flow. The change in shock cell spacing, which occurs with an intrusive tab, does not occur when screech is cancelled with the new technique. The broadband shock-associated noise is also influenced much less when the jet screech tones are eliminated by the new method.

Nagel, R. T.↗
NASA NTRS1972

Relations among pure-tone sound stimuli, neural activity, and the loudness sensation

Both the physiological and psychological responses to pure-tone sound stimuli are used to derive formulas which: (1) relate the loudness, loudness level, and sound-pressure level of pure tones; (2) apply continuously over most of the acoustic regime, including the loudness threshold; and (3) contain no undetermined coefficients. Some of the formulas are fundamental for calculating the loudness of any sound. Power-law formulas relating the pure-tone sound stimulus, neural activity, and loudness are derived from published data.

Howes, W. L.↗
NASA NTRS1996

Active Control of Fan Noise: Feasibility Study: Flyover System Noise Studies - Volume 4

An extension of a prior study has been completed to examine the potential reduction of aircraft flyover noise by the method of active noise control (ANC). It is assumed that the ANC system will be designed such that it cancels discrete tones radiating from the engine fan inlet or fan exhaust duct, at least to the extent that they no longer protrude above the surrounding broadband noise levels. Thus, without considering the engineering details of the ANC system design, tone levels am arbitrarily removed from the engine component noise spectrum and the flyover noise EPNL levels are compared with and without the presence of tones. The study was conducted for a range of engine cycles, corresponding to fan pressure ratios of 1.3, 1.45, 1.6, and 1.75. This report is an extension of an effort reported previously. The major conclusions drawn from the prior study, which was restricted to fan pressure ratios of 1.45 and 1.75, are that, for a fan pressure ratio of 1.75, ANC of tones gives about the same suppression as acoustic treatment without ANC. For a fan pressure ratio of 1.45, ANC appears to offer less effectiveness from passive treatment. In the present study, the other two fan pressure ratios are included in a more detailed examination of the benefits of the ANC suppression levels. The key results of this extended study are the following observations: (1) The maximum overall benefit obtained from suppression of BPF alone was 2.5 EPNdB at high fan speeds. The suppression benefit increases with increase in fan pressure ratio (FPR), (2) The maximum overall benefit obtained from suppression of the first three harmonics was 3 EPNdB at high speeds. Suppression benefit increases with increase in FPR, (3) At low FPR, only about 1.0 EPNdB maximum reduction was obtained. Suppression is primarily from reduction of BPF at high FPR values and from the combination of tones at low FPR, (4) The benefit from ANC is about the same as the benefit from passive treatment at fan pressure ratios of 1.75 and 1.60. At the two lower fan pressure ratios, the effectivness of treatment is much greater than that of ANC, and (5) No significant difference in ANC suppression behavior was found from the QCSEE engine database analysis compared to that of the E3 engine database, for the FPR = 1.3 engine cycle. The effects of ANC on EPNL noise reduction are difficult to generalize. It was found that the reduction obtained in any particular case depended upon the frequency of the tones and their shift with rpm, the amount of ANC suppression received by each tone (which depended on its protrusion from the background), and the NOY-value of the tone relative to the NOY-value of other tones and the peak broadband levels, because PNL is determined from the sum of the NOY-values.

Kraft, R. E.↗
NASA NTRS1987

Parameter estimation based on Doppler frequency shifts

An acoustic source generates an amplitude-modulated tone, with Doppler variations due to the relative motion between source and receiver. A method is presented for real-time estimation of tone rest frequency and minimal distance between source and receiver, using digital signal processing techniques. The algorithm presented here was implemented using a Texas Instruments TMS32010 processor.

Statman, Joseph I.↗
NASA NTRS2006

Assessment of Bulk Absorber Properties for Multi-Layer Perforates in Porous Honeycomb Liners

CONTINUING progress in materials technology provides potential for improved acoustic liners for attenuating broadband fan noise emissions from aircraft engine nacelles. Conventional liners (local-reacting perforate-over-honeycomb structures) provide significant narrow-band attenuation, but limited attenuation over wide bandwidths. Two approaches for increasing attenuation bandwidth are to (1) replace the honeycomb structure with bulk material, or (2) cascade multiple layers of perforate/honeycomb structures. Usage of the first approach is limited because of mechanical and maintenance reasons, while multi-layer liners are limited to about three layers because of their additional mechanical complexity, depth and weight. The current research concerns a novel approach reported by the University of Cincinnati, in which a single-layer conventional liner is converted into an extended-reaction, broadband absorber by making the honeycomb core structure porous. This modified single-layer liner requires no increase in depth and weight, and minimal increase in mechanical complexity. Langley has initiated research to identify potential benefits of liner structures with porous cell walls. This research has two complementary goals: (1) develop and validate experimental techniques for treating multi-layer perforates (representative of the internal cells of a liner with porous cell walls) as 1-D bulk materials, and (2) develop analytical approaches to validate this bulk material assumption. If successful, the resultant model can then be used to design optimized porous honeycomb liners. The feasibility of treating an N-layer perforate system (N porous plates separated by uniform air gaps) as a one-dimensional bulk absorber is assessed using the Two-Thickness Method (TTM), which is commonly used to educe bulk material intrinsic acoustic parameters. Tests are conducted with discrete tone and random noise sources, over an SPL range sufficient to determine the nonlinearity of the test specimens, for test specimens consisting of 5, 10 and 15% porous plates. Measured impedances for two liner thicknesses (e.g., 12 and 24 layers) are used as input to the TTM to determine the characteristic impedance and propagation constant that characterize these liners as bulk absorbers. These parameters are then used to calculate the predicted impedance of liners with different thicknesses (e.g., 36 layers), and a comparison of predicted and measured impedances for these other thicknesses is used to determine the efficacy of this approach. Finally, an independent method is used to educe the propagation constant for a single representative sample, and excellent comparison between the results for this method and those for the TTM provides increased confidence in the results achieved with the TTM. In general, the results demonstrate these multi-layer perforates can be acceptably treated as bulk absorbers.

Jones, Michael G.↗
NASA NTRS1993

Comparison of measured and predicted pure tone propagation levels from JAPE-1: An evaluation of the performance of ASOPRAT

Joint Acoustic Propagation Experiment Phase One (JAPE-1 ) short range propagation data has been used to evaluate the performance of the Advanced Sound Propagation in the Atmosphere (ASOPRAT) prediction code. The pure tone short range data was Fourier analyzed giving the propagated pressure levels as a function of frequency. Meteorological profiles measured at the experimental site were used as input for the acoustic prediction routine ASOPRAT. Predicted and measured propagation levels are compared in decibels (dB) relative to one of the measurement positions for receivers on the line passing between the two thirty meter towers. Agreement between predicted and measured levels is very good. Source strength data was not available, hence the comparisons show good agreement as to the shape of the propagation loss curve not necessarily the propagation levels.

Frederickson, Carl K.↗