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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Jet noise predictions from unsteady Navier-Stokes simulations

Numerical solutions of the Navier-Stokes equations are employed to predict the characteristics of round jets at supersonic speeds. The simulations are performed with a finite volume method which is fourth order accurate in space and second order in time. The overall sound pressure level (OASPL) in the near field of a round free jet is over-predicted by roughly 8 dB relative to an experimental correlation. In an impinging jet, shock motion and vortex stretching are identified as noise generation mechanisms in the impingement zone.

Childs, Robert E.↗
NASA NTRS2011

Wet active chevron nozzle for controllable jet noise reduction

Disposed at or toward the trailing edge of one or more nozzles associated with a jet engine are injection ports which can selectively be made to discharge a water stream into a nozzle flow stream for the purpose of increasing turbulence in somewhat of a similar fashion as mechanically disposed chevrons have done in the known art. Unlike mechanically disposed chevrons of the known art, the fluid flow may be secured thereby increasing the engine efficiency. Various flow patterns, water pressures, orifice designs or other factors can be made operative to provide desired performance characteristics.

Thomas, Russell H.↗
NASA NTRS2018

Subsonic Jet Noise Simulation with JENRE

JENRE, a large eddy simulation code, is used to simulate an unheated, subsonic jet. Results are compared to experiment, with an emphasis on validating the acoustic power spectral density at the farfield. Problems encountered during the development of the simulations are discussed, with solutions to said problems.

Ingraham, Daniel↗
NASA NTRS1991

Short conical solid/perforated plug-nozzle as supersonic jet noise suppressor

Experimental studies of the acoustic far field, and the nature of the repetitive shock structure in cold jet flows from an externally expanded plug-nozzle having a short conical plug with a pointed termination, operated in a range of supercritical pressure ratios of 2.0 to 4.5, are reported. The overall sound pressure levels of a short solid conical plug-nozzle (CPN) are found to be within 3 dB of those of the baseline noise levels of a minimum length contoured plug-nozzle operated at the same pressure ratio and having the same annular throat area. As compared to an equivalent convergent nozzle, the noise reductions achieved through the use of a short solid CPN are of the order of 5 dB.

Das, I. S.↗
NASA NTRS1975

The low frequency sound from multipole sources in axisymmetric shear flows, with applications to jet noise

A closed-form solution for the sound radiation from multipole sources imbedded in an infinite cylindrical jet with an arbitrary velocity profile is obtained. It is valid in the limit where the wavelength is large compared with the jet radius. Simple formulae for the acoustic pressure field due to convected point sources are also obtained. The results show (in a simple way) how the mean flow affects the radiation pattern from the sources. For convected lateral quadrupoles it causes the exponent of the Doppler factor multiplying the far-field pressure signal to be increased from the value of 3 used by Lighthill to 5.

Goldstein, M. E.↗
NASA NTRS2001

Simulation of Supersonic Jet Noise with the Adaptation of Overflow CFD Code and Kirchhoff Surface Integral

An acoustic prediction capability for supersonic axisymmetric jets was developed on the basis of OVERFLOW Navier-Stokes CFD (Computational Fluid Dynamics) code of NASA Langley Research Center. Reynolds-averaged turbulent stresses in the flow field are modeled with the aid of Spalart-Allmaras one-equation turbulence model. Appropriate acoustic and outflow boundary conditions were implemented to compute time-dependent acoustic pressure in the nonlinear source-field. Based on the specification of acoustic pressure, its temporal and normal derivatives on the Kirchhoff surface, the near-field and the far-field sound pressure levels are computed via Kirchhoff surface integral, with the Kirchhoff surface chosen to enclose the nonlinear sound source region described by the CFD code. The methods are validated by a comparison of the predictions of sound pressure levels with the available data for an axisymmetric turbulent supersonic (Mach 2) perfectly expanded jet.

Kandula, Max↗
NASA NTRS2004

Design, Fabrication, and Testing of SMA Enabled Adaptive Chevrons for Jet Noise Reduction

This study presents the status and results from an effort to design, fabricate, and test an adaptive jet engine chevron concept based upon embedding shape memory alloy (SMA) actuators in a composite laminate, termed a SMA hybrid composite (SMAHC). The approach for fabricating the adaptive SMAHC chevrons involves embedding prestrained Nitinol actuators on one side of the mid-plane of the composite laminate such that thermal excitation generates a thermal moment and deflects the structure. A glass-epoxy pre-preg/Nitinol ribbon material system and a vacuum hot press consolidation approach are employed. A versatile test system for control and measurement of the chevron deflection performance is described. Projection moire interferometry (PMI) is used for global deformation measurement and infrared (IR) thermography is used for 2-D temperature measurement and feedback control. A recently commercialized constitutive model for SMA and SMAHC materials is used in the finite element code ABAQUS to perform nonlinear static analysis of the chevron prototypes. Excellent agreement is achieved between the predicted and measured chevron deflection performance, thereby validating the design tool. Although the performance results presented in this paper fall short of the requirement, the concept is proven and an approach for achieving the performance objectives is evident.

Turner, Travis L.↗
NASA NTRS1984

Large-scale coherent structure and far-field jet noise

The phenomenon of broadband noise amplification/suppression under controlled excitation is investigated. The suppression is found to occur only at low jet speeds when the exit boundary layer is laminar; excitation at a Strouhal St(theta) number of about 0.017 results in optimum suppression of the far-field broadband noise as well as of the near-flow-field turbulence. The noise amplification is found to be a function of the Mach number, the amplification is higher at higher Mach number for a given excitation Strouhal number and level. The amplification also depends on the Strouhal number (St D), the maximum occurring in the range 0.65-0.85. Vortex pairing induced by the excitation appears to be at the heart of the noise amplification phenomenon under excitation.

Zaman, K. B. M. Q.↗
NASA NTRS2012

Advanced Jet Noise Exhaust Concepts in NASA's N+2 Supersonics Validation Study and the Environmentally Responsible Aviation Project's Upcoming Hybrid Wing Body Acoustics Test

Acoustic and flow-field experiments were conducted on exhaust concepts for the next generation supersonic, commercial aircraft. The concepts were developed by Lockheed Martin (LM), Rolls-Royce Liberty Works (RRLW), and General Electric Global Research (GEGR) as part of an N+2 (next generation forward) aircraft system study initiated by the Supersonics Project in NASA s Fundamental Aeronautics Program. The experiments were conducted in the Aero-Acoustic Propulsion Laboratory at the NASA Glenn Research Center. The exhaust concepts presented here utilized lobed-mixers and ejectors. A powered third-stream was implemented to improve ejector acoustic performance. One concept was found to produce stagnant flow within the ejector and the other produced discrete-frequency tones (due to flow separations within the model) that degraded the acoustic performance of the exhaust concept. NASA's Environmentally Responsible Aviation (ERA) Project has been investigating a Hybrid Wing Body (HWB) aircraft as a possible configuration for meeting N+2 system level goals for noise, emissions, and fuel burn. A recently completed NRA led by Boeing Research and Technology resulted in a full-scale aircraft design and wind tunnel model. This model will be tested acoustically in NASA Langley's 14-by 22-Foot Subsonic Tunnel and will include dual jet engine simulators and broadband engine noise simulators as part of the test campaign. The objectives of the test are to characterize the system level noise, quantify the effects of shielding, and generate a valuable database for prediction method development. Further details of the test and various component preparations are described.

Henderson, Brenda S.↗
NASA NTRS1971

The structure of jet turbulence producing jet noise

The structure of the turbulence in the mixing region for the first few diameters downstream from the outlet of a circular subsonic jet is characterized at three Mach numbers, 0.3, 0.5, and 0.7, with most of the measurements taken at M = 0.3. Profiles of turbulence intensity showed that downstream of the lip intensity is independent of axial distance, while in the core intensity varies by a factor of eight between the jet outlet and the end of the core. A digital data reduction program was used to calculate the auto- and cross-correlations of axial velocity fluctuations and the power spectral densities. Convection velocities were measured using broadband, hot wire signals and signals that were digitally filtered for band-passes about center frequencies of 0.8, 1.3, 1.6, and 3.2 kHz. The center frequency of 1.3 kHz corresponded to the peak energy in the core spectrum. The results support the hypothesis that the coherent pressure field is driven by the intermittent fluctuations at the core boundary, which in turn are related to the large (low frequency) eddies.

Wooldridge, C. E.↗
NASA NTRS1974

A model for jet-noise analysis using pressure-gradient correlations on an imaginary cone

The technique for determining the near and far acoustic field of a jet through measurements of pressure-gradient correlations on an imaginary conical surface surrounding the jet is discussed. The necessary analytical developments are presented, and their feasibility is checked by using a point source as the sound generator. The distribution of the apparent sources on the cone, equivalent to the point source, is determined in terms of the pressure-gradient correlations.

Norum, T. D.↗
NASA NTRS1973

Investigation of coaxial jet noise and inlet choking using an F-111A airplane

Measurements of engine noise generated by an F-111A airplane positioned on a thrustmeasuring platform were made at angles of 0 deg to 160 deg from the aircraft heading. Sound power levels, power spectra, and directivity patterns are presented for jet exit velocities between 260 feet per second and 2400 feet per second. The test results indicate that the total acoustic power was proportional to the eighth power of the core jet velocity for core exhaust velocities greater than 300 meters per second (985 feet per second) and that little or no mixing of the core and fan streams occurred. The maximum sideline noise was most accurately predicted by using the average jet velocity for velocities above 300 meters per second (985 feet per second). The acoustic power spectrum was essentially the same for the single jet flow of afterburner operation and the coaxial flow of the nonafterburning condition. By varying the inlet geometry and cowl position, reductions in the sound pressure level of the blade passing frequency on the order of 15 decibels to 25 decibels were observed for inlet Mach numbers of 0.8 to 0.9.

Putnam, T. W.↗
NASA NTRS1980

Application of optical methods to the study of jet noise and turbulence

Optical methods are generally applied in fluid mechanics for either visualization or measurement. The use of a laser anemometer to study flow velocity in a jet and its relaton to the sound radiated is described. The same acoustic emission phenomenon is also measued by combining the signals from four Schlieren systems with that from an interferometer. The use of an optical Fourier transformation approach with real time analysis to determine the spatio-temporal structure of a field of mass volume such as a waveguide or free jet is also examined.

Sava, P. G.↗
NASA NTRS2003

Computation of Large-Scale Structure Jet Noise Sources With Weak Nonlinear Effects Using Linear Euler

An approximate technique is presented for the prediction of the large-scale turbulent structure sound source in a supersonic jet. A linearized Euler equations code is used to solve for the flow disturbances within and near a jet with a given mean flow. Assuming a normal mode composition for the wave-like disturbances, the linear radial profiles are used in an integration of the Navier-Stokes equations. This results in a set of ordinary differential equations representing the weakly nonlinear self-interactions of the modes along with their interaction with the mean flow. Solutions are then used to correct the amplitude of the disturbances that represent the source of large-scale turbulent structure sound in the jet.

Dahl, Milo D.↗
NASA NTRS1999

Large Eddy Simulation in the Computation of Jet Noise

Noise can be predicted by solving Full (time-dependent) Compressible Navier-Stokes Equation (FCNSE) with computational domain. The fluctuating near field of the jet produces propagating pressure waves that produce far-field sound. The fluctuating flow field as a function of time is needed in order to calculate sound from first principles. Noise can be predicted by solving the full, time-dependent, compressible Navier-Stokes equations with the computational domain extended to far field - but this is not feasible as indicated above. At high Reynolds number of technological interest turbulence has large range of scales. Direct numerical simulations (DNS) can not capture the small scales of turbulence. The large scales are more efficient than the small scales in radiating sound. The emphasize is thus on calculating sound radiated by large scales.

Mankbadi, R. R.↗
NASA NTRS1960

Transonic Performance Characteristics of Several Jet Noise Suppressors

An investigation of the transonic performance characteristics of several noise-suppressor configurations has been conducted in the Langley 16-foot transonic tunnel. The models were tested statically and over a Mach number range from 0.70 to 1.05 at an angle of attack of 0 deg. The primary jet total-pressure ratio was varied from 1.0 (jet off) to about 4.5. The effect of secondary air flow on the performance of two of the configurations was investigated. A hydrogen peroxide turbojet-engine simulator was used to supply the hot-jet exhaust. An 8-lobe afterbody with centerbody, short shroud, and secondary air had the highest thrust-minus-drag coefficients of the six noise-suppressor configurations tested. The 12-tube and 12-lobe afterbodies had the lowest internal losses. The presence of an ejector shroud partially shields the external pressure distribution of the 8-lobe after-body from the influence of the primary jet. A ring-airfoil shroud increased the static thrust of the annular nozzle but generally decreased the thrust minus drag at transonic Mach numbers.

Schmeer, James W.↗
NASA NTRS1976

Numerical evaluation of the jet noise source distribution from far-field cross correlations

This paper contains the development of techniques to determine the relationship between the unknown source correlation function to the correlation of scattered amplitudes in a jet. This study has application to the determination of forward motion effects. The technique has been developed and tested on a model jet of high subsonic flow. Numerical solution was obtained by solving the Fredholm integral equation of the first kind. Interpretation of the apparent source distribution and its application to flight testing are provided.

Maestrello, L.↗