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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 NTRS1993

The structure of supersonic jet flow and its radiated sound

Large-eddy simulation of a supersonic jet is presented with emphasis on capturing the unsteady features of the flow pertinent to sound emission. A high-accuracy numerical scheme is used to solve the filtered, unsteady, compressible Navier-Stokes equations while modelling the subgrid-scale turbulence. For random inflow disturbance, the wave-like feature of the large-scale structure is demonstrated. The large-scale structure was then enhanced by imposing harmonic disturbances to the inflow. The limitation of using the full Navier-Stokes equation to calculate the far-field sound is discussed. Application of Lighthill's acoustic analogy is given with the objective of highlighting the difficulties that arise from the non-compactness of the source term.

Mankbadi, Reda R.↗
NASA NTRS1995

Nonlinear Stability of Supersonic Jets

This paper presents stability calculations made for a shock-free supersonic jet using the model based on parabolized stability equations. In this analysis the large-scale structures, which play a dominant role in the mixing as well as the noise radiated, are modeled as instability waves. This model takes into consideration non-parallel flow effects and also nonlinear interaction of the instability waves. The stability calculations have been performed for different frequencies and mode numbers over a range of jet operating temperatures. Comparisons are made, where appropriate, with the solutions to Rayleigh's equation (linear, inviscid analysis with the assumption of parallel flow). The comparison of the solutions obtained using the two approaches show very good agreement.

Bhat, T. R. S.↗
NASA NTRS1997

Multi-Axis Fluidic Thrust Vectoring of a Supersonic Jet Using Counterflow

The most common techniques currently used to efficiently vector supersonic jets require external flaps and or pivoting devices. Fluidic thrust vectoring using counterflow eliminates the need for such complex hardware. Thus, the promise of decreases in both weight and drag as well as increased maneuverability makes this technique an attractive alternative. This technique has been successfully employed to achieve single axis fluidic thrust vectoring of a Mach 2 rectangular jet. To better compete with contemporary systems the current study extends this technique to multi-axis thrust vectoring of a Mach 2 diamond-shaped jet by applying counterflow to one of its four sides. To evaluate the performance of this technique the Planar Laser Scattering (PLS) technique is used to show the continuous vectoring of the diamond jet up to 20 degrees. Also, cross-stream PLS images are acquired to show the vectoring can be achieved off all four surfaces of the diamond jet.

Barber, Edward L.↗
NASA NTRS1984

Interactive phenomena in supersonic jet mixing problems. II - Numerical studies

Applications of the numerical techniques discussed in Part I of this article are presented. Fundamental wave/shear-layer interaction calculations are performed exhibiting the waves produced by high-speed turbulent mixing processes and the interactions of an expansion fan and shock wave with a developing shear layer. Calculations for an underexpanded supersonic jet into a supersonic external stream at different velocity ratios are presented which delineate betweeen weakly interactive and strongly interactive processes in the jet near field. Calculations for the multiple-cell shock structure of an underexpanded jet into still air exhibit the damping of wave intensities by the turbulence and compare quite favorably with available data.

Dash, S. M.↗
NASA NTRS1977

The flow field of an underexpanded H2 jet coaxially injected into a hot free or ducted supersonic jet of air or nitrogen

Experimental data obtained in an investigation of the mixing of an underexpanded hydrogen jet in a supersonic flow both with and without combustion are presented. Tests were conducted in a Mach 2 test stream with both air and nitrogen as test media. Total temperature of the test stream was 2170 K, and static exit pressure was about one atmosphere. The static pressure at the exit of the hydrogen injector's Mach 2 nozzle was about two atmospheres. Primary measurements included shadowgraphs and pitot pressure surveys of the flow field. Pitot surveys and wall static pressures were measured for the case where the entire flow was shrouded. The results are compared to similar experimental data and theoretical predictions for the matched pressure case.

Jenkins, R. V.↗
NASA NTRS1980

Instability process in low Reynolds number supersonic jets

The objective of the present research was to characterize the instability of supersonic jets of Mach numbers 1.4, 2.1, and 2.5 in the Reynolds number range around 8000. In this Reynolds number range the jet instability has its maximum coherence so that its properties as well as the acoustic properties can be most clearly identified. Growth rate, wavelength, and wave orientation of dominant spectral components of the instability for the three Mach number jets were measured in order to characterize the instability. The saturation and subsequent decay on the instability are coincident with a drastic decrease in the coherence of the instability. Associated research shows that the phenomenon of rapid growth and decay is of fundamental importance in the noise generation process.

Morrison, G. L.↗
NASA NTRS1989

The resonance of twin supersonic jets

This paper presents an analytical study of the resonant interaction between twin supersonic jets. An instability wave model is used to describe the large scale coherent structures in the jet mixing layers. A linearized shock cell model is also given for the jets when operating off design. The problem's geometry admits four types of normal modes associated with each azimuthal mode number in the single jet. The stability of these modes is examined for both a vortex sheet model of the jet and a jet flow represented by realistic profiles. The growth rates of each mode number and type are found to vary with jet separation and mixing layer thickness and Strouhal number. Contours of equal pressure level are obtained for each mode. The region close to the symmetry axis is found to have the greatest pressure fluctuation amplitude.

Morris, Philip J.↗
NASA NTRS1990

Broadband shock-associated noise of moderately imperfectly expanded supersonic jets

Recently a stochastic model theory of broadband shock-associated noise from supersonic jets was developed. The theory is capable of predicting the near and far field noise spectra of slightly imperfectly expanded jets. In this paper, the noise prediction formulas are extended to the moderately imperfectly expanded Mach number range. It is found that the shock noise intensity depends only on the amplitude of the quasi-periodic shock cell structure and not on the strong first shock. This makes it possible to extend the noise prediction formulas by simply modifying the shock cell strength in the original formulas. Here this step is implemented semiempirically, and a set of shock noise prediction formulas are developed.

Tam, C. K. W.↗
NASA NTRS1973

Geometric factors affecting noise suppresion and thrust loss of divergent-lobe supersonic jet noise suppressor

The thrust loss and noise suppression of a divergent-lobe supersonic jet noise suppressor were experimentally determined over a range of nozzle pressure ratios of 1.5 to 4.0. These small-scale cold flow tests were made to determine the effect on thrust and noise of: suppressor length, rearward facing step height, suppressor divergence angle, and ejector shroud length and location. Noise suppression was achieved at nozzle pressure ratios of 2.5 and greater. Maximum lobe jet noise attenuation of 15 db with thrust loss differences of 1.5 percent compared to the convergent nozzle were obtained at a nozzle pressure ratio of 3.5 with an ejector shroud two nozzle diameters long. Without the ejector the attenuation was 13 db with thrust loss differences of 11 percent. Short suppressors approximately one primary nozzle throat diameter long performed as well as longer suppressors. Rearward facing step height had a significant effect on noise suppression. Ejector shrouds two nozzle diameters in length are feasible.

Huff, R. G.↗
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 NTRS1990

Flow and acoustic properties of low Reynolds number underexpanded supersonic jets

An experimental program to investigate the flow and acoustic properties of model underexpanded supersonic jets was conducted. In particular, the role played by large-scale organized fluctuations in the flow evolution and acoustic production processes was examined in detail. The experimental conditions were chosen as low-Reynolds-number (Re = 8000) Mach 1.4 and 2.1 underexpanded jets exhausting from convergent nozzles. A consequence of performing the experiments at low Reynolds number is that the broadband shock-associated noise is suppressed. The focus of the present study is on the generation of noise by large-scale instabilities in the presence of strong shock cell structures. It is demonstrated that the production of screech is related to the modulation and decay of large-scale turbulence structures.

Hu, Tieh-Feng↗
NASA NTRS1992

Broadband shock associated noise from supersonic jets measured by a ground observer

The theory of broadband shock associated noise from supersonic jets in flight previously developed in the nozzle fixed coordinates is extended to the coordinate system of a stationary ground observer. The extended theory is relevant to community noise and aircraft certification noise prediction. Since the noise source is unaffected by which coordinate system of reference the radiated noise is measured, the same noise source model is retained in the present formulation. Only kinematic arguments are needed in the analysis. A formula for the noise power spectrum as measured by a ground observer is derived. The formula is applicable to hot as well as cold jets. This formula exhibits a form of Doppler shift in the noise spectrum. However, there is no high power convective amplification factor as some other investigators have proposed.

Tam, Christopher K. W.↗
NASA NTRS1996

Computational aeroacoustics and numerical simulation of supersonic jets

The research project has been a computational study of computational aeroacoustics algorithms and numerical simulations of the flow and noise of supersonic jets. During this study a new method for the implementation of solid wall boundary conditions for complex geometries in three dimensions has been developed. In addition, a detailed study of the simulation of the flow in and noise from supersonic circular and rectangular jets has been conducted. Extensive comparisons have been made with experimental measurements. A summary of the results of the research program are attached as the main body of this report in the form of two publications. Also, the report lists the names of the students who were supported by this grant, their degrees, and the titles of their dissertations. In addition, a list of presentations and publications made by the Principal Investigators and the research students is also included.

Morris, Philip J.↗
NASA NTRS1993

Enhanced mixing of a rectangular supersonic jet by natural and induced screech

The influence of shear layer excitation on the mixing of supersonic rectangular jets was studied experimentally. Two methods of excitation were used to control the jet mixing. The first used the natural screech of an underexpanded supersonic jet from a converging nozzle. The level of the screech excitation was controlled by the use of a pair of baffles located to block the acoustic feedback path between the downstream shock structure and the nozzle lip. A screech level variation of over 30 decibels was achieved and the mixing was completely determined by the level of screech attained at the nozzle lip. The second form of self-excitation used the induced screech caused by obstacles or paddles located in the shear layers on either long side of the rectangular jet. With sufficient immersion of the paddles intense jet mixing occurred and large flapping wave motion was observed using a strobed focused Schlieren system. Each paddle was instrumented with a total pressure tap and strain gages to determine the pressure and drag force on the square cross-section paddle. Considerable drag was observed in this initial exploratory study. Future studies using alternate paddle geometries will be conducted to maximize jet mixing with minimum drag.

Rice, Edward J.↗
NASA NTRS1975

Density fluctuations and radiated noise for a high-temperature supersonic jet

Experimental data on density fluctuations were obtained by the laser Schlieren method in a supersonic jet which at the nozzle exit had a Mach number of 1.43 and a stagnation temperature of about 1090 K. The jet emerged into the ambient atmosphere in an anechoic chamber, correctly expanded from a nozzle which had an exit diameter of 10.8 cm. Using the information on the density fluctuations and the mean shear obtained by probes, the autocorrelation of the radiated noise was calculated by a theory that is suitable for Mach wave emission. This theory is a modification of that developed by Ffowcs Williams and Maidanik (1965). The calculated noise field agrees well with that obtained by using microphones outside the jet.

Parthasarathy, S. P.↗
NASA NTRS1982

Measurements of Mean Static Pressure and Far Field Acoustics of Shock Containing Supersonic Jets

The far field acoustic data base generated in studies of broadband shock noise from supersonic jets is presented. Both conical and contoured nozzles of exit Mach numbers 1.0, 1.5, and 2.0 were tested using unheated air at pressure ratios ranging from 1.9 to 14. Tests were performed both with and without screech suppression tabs. Overall sound pressure variations and representative 1/3-octave and narrowband spectra are presented. The mean static pressure measured within these jets is also surveyed.

Norum, T. D.↗
NASA NTRS1999

Prediction, Measurement, and Suppression of High Temperature Supersonic Jet Noise

The photograph in figure 1 displays a water cooled round convergent-divergent supersonic nozzle operating slightly overexpanded near 2460 F. The nozzle is designed to produce shock free flow near this temperature at Mach 2. The exit diameter of this nozzle is 3.5 inches. This nozzle is used in the present study to establish properties of the sound field associated with high temperature supersonic jets operating fully pressure balanced (i.e. shock free) and to evaluate capability of the compressible Rayleigh model to account for principle physical features of the observed sound emission. The experiment is conducted statically (i.e. M(sub f) = 0.) in the NASA/LaRC Jet Noise Laboratory. Both aerodynamic and acoustic measurements are obtained in this study along with numerical plume simulation and theoretical prediction of jet noise. Detailed results from this study are reported previously by Seiner, Ponton, Jansen, and Lagen.

Seiner, John M.↗
NASA NTRS2011

Flow Field Characterization of an Angled Supersonic Jet Near a Bluff Body

An experiment was performed to acquire data from a hot supersonic jet in cross flow for the purpose of validating computational fluid dynamics (CFD) turbulence modeling relevant to the Orion Launch Abort System. Hot jet conditions were at the highest temperature and pressure that could be acquired in the test facility. The nozzle pressure ratio was 28.5, and the nozzle temperature ratio was 3. These conditions are different from those of the flight vehicle, but sufficiently high to model the observed turbulence features. Stereo Particle Image Velocimetry (SPIV) data and capsule pressure data are presented. Features of the flow field are presented and discussed

Wolter, John D.↗