Liquid fuel jet in subsonic crossflow
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Nguyen, T. T.↗
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Effects of pressure-rake design parameters on static-pressure measurement for rakes used in subsonic free jets
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Krause, Lloyd N↗
Unsteady jet flow computation towards noise prediction
An attempt has been made to combine a wave solution method and an unsteady flow computation to produce an integrated aeroacoustic code to predict far-field jet noise. An axisymmetric subsonic jet is considered for this purpose. A fourth order space accurate Pade compact scheme is used for the unsteady Navier-Stokes solution. A Kirchhoff surface integral for the wave equation is employed through the use of an imaginary surface which is a circular cylinder enclosing the jet at a distance. Information such as pressure and its time and normal derivatives is provided on the surface. The sound prediction is performed side by side with the jet flow computation. Retarded time is also taken into consideration since the cylinder body is not acoustically compact. The far-field sound pressure has the directivity and spectra show that low frequency peaks shift toward higher frequency region as the observation angle increases from the jet flow axis.
Soh, Woo-Yung↗
Noise, Turbulence, and Thrust of Subsonic Free Jets from Lobed Nozzles
A study of noise benefit, vis-a-vis thrust penalty, and its correlation to turbulence intensities was conducted for free jets issuing from lobed nozzles. Four convergent nozzles with constant exit area were used in the experiments. Three of these were of rectangular lobed configuration having six, ten and fourteen lobes; the fourth was a circular nozzle. Increasing the number of lobes resulted in a progressive reduction in the turbulence intensities as well as in the overall radiated noise. The noise reduction was pronounced at the low frequency end of the spectrum. However, there was an increase in the high frequency noise that rendered the overall benefit less attractive when compared on a scaled-up A-weighted basis. A reduction in noise was accompanied by a commensurate reduction in the turbulent kinetic energy in the flow field. As expected, increasing the number of lobes involved progressive reduction in the thrust coefficient. Among the cases studied, the six-lobed nozzle had the optimum reduction in turbulence and noise with the least thrust penalty.
Zaman, K. B. M. Q.↗
Vorticity associated with multiple jets in a crossflow
Vortex patterns from multiple subsonic jets exiting perpendicularly through a flat plate into a subsonic crossflow were investigated. Tandem and transverse jet configurations were examined using a paddle wheel sensor to indicate the presence and relative magnitude of streamwise vorticity in the flow. Results are presented in the form of contour plots of rotational speed of the paddle wheel as measured in planes downstream from the jets and perpendicular to the crossflow. Well developed diffuse contrarotating vortices were observed for the configurations studied. The location and strength of these vortices depended on the multiple jet configuration and the distance downstream from the jets.
Braden, S.↗
Response of a Panel Structure Forced by the Noise from a Nearly Sonic Jet
A model of a high subsonic jet with a nearby array of flexible, aircraft-type panels is studied numerically in two dimensions. The jet is excited by a limited duration, spatially localized starter pulse in the potential core. The long time evolution of unsteady disturbances in the jet, the responses of the panels, and the ensuing radiation are computed. The results show that the spectral response of both the jet and the panels is concentrated in a relatively narrow frequency band centered at a Strouhal number (based on jet exit velocity) of approximately 0.25 and associated harmonics. The loading on the panels generally increases with downstream distance. Panel radiation is weakest in upstream directions. Interior zones of silence, due to destructive interference of radiation from the panels, are observed.
Fenno, C. C., Jr.↗
Response of a Panel Structure Forced by the Noise from a Nearly Sonic Jet
A model of a high subsonic jet with a nearby array of exible, aircraft-type panels is studied numerically in two dimensions. The jet is excited by a limited duration, spatially localized starter pulse in the potential core. The long time evolution of unsteady disturbances in the jet, the responses of the panels and the ensuing radiation are computed. The results show that the spectral response of both the jet and the panels is concentrated in a relatively narrow frequency band centered at a Strouhal number (based on jet exit velocity) of approximately 0.25 and associated harmonics. The loading on the panels generally increases with downstream distance. Panel radiation is weakest in upstream directions. Interior zones of silence, due to destructive interference of radiation from the panels, are observed.
Fenno, C. C., Jr.↗
Jet-Surface Interaction Test: Phased Array Noise Source Localization Results
Subsonic jets are relatively simple. The peak noise source location gradually moves upstream toward the nozzle as frequency increases. 2) Supersonic jets are more complicated. The peak noise source location moves downstream as frequency increases through a BBSN hump. 3) In both subsonic and supersonic jets the peak noise source location corresponding to a given frequency of noise moves downstream as jet Mach number increases. 4) The noise generated at a given frequency in a BBSN hump is generated by a small number of shocks, not from all the shocks at the same time. 5) Single microphone spectrum levels decrease when the noise source locations measured with the phased array are blocked by a shielding surface. This consistency validates the phased array data and the stationary monopole source model used to process it. 6) Reflecting surface data illustrate that the law of reflection must be satisfied for noise to reflect off a surface toward an observer. Depending on the relative locations of the jet, the surface and the observer only some of the jet noise sources may satisfy this requirement. 7) The low frequency noise created when a jet flow impinges on a surface comes primarily from the trailing edge regardless of the axial extent impacted by the flow.
Podboy, Gary↗
Development of an analytical model for the flow of a jet into a subsonic crosswind
Mathematical model for jet flow into subsonic crosswind
Wooler, P. T.↗
Analytical study of twin-jet shielding
Progress in the refinement and evaluation of an analytical jet shielding model are summarized. The model consists of a point noise source impinging on a cylinder of heated flow in which the temperature and velocity are uniform across the cross section of the jet. The shielding jet is infinite in extent along the jet axis and the radius of the jet is constant. The analytical model was compared to experimental data for a point noise source impinging on an ambient temperature, subsonic jet and on a subsonic simulated hot jet using helium as the flow medium. Results of these comparisons are discussed.
Gerhold, C. H.↗
Computing Jet-Exhaust/Crossflow Interactions
JETPLT and JETBOD programs developed to predict velocity and pressure induced by subsonic jets exhausting into subsonic free stream. JETPLT predicts pressures induced on infinite flat plate by jet exhausting at angles to plate. JETBOD, in conjunction with panel code, predicts pressures induced on body of revolution by jet exhausting perpendicularly to surface. Programs used to investigate interactions between jet exhausts and crossflows in vertical/short-takeoff-andlanding aircraft shifting from hover to forward flight, where inducedpressure loading leads to reduction in lift. JETPLT/JETBOD written in FORTRAN 77.
Perkins, S. C., Jr.↗
Acoustic wave propagation in an axisymmetric swirling jet.
An analysis has been developed to study the acoustic wave propagation in an axisymmetric swirling subsonic jet flow. The governing convected wave equation derived in the spherical coordinates includes mean shears, shear gradients and pressure gradients. The directivity patterns for various spinning and non-spinning modes due to the influence of the mean jet swirl were obtained by numerically integrating the governing wave equation. The mean flow field used in the computation was that obtained semiempirically for subsonic swirling turbulent jet and is completely specified once the degree of swirl is known. The dependence of sound directivity on jet Mach number, swirl ratio and frequency are discussed.
Yu, J. C.↗
A blockage-sink representation of jet interference effects for noncircular jet orifices
Two dimensional potential flow representation of subsonic jet interference effects for jet orifice
Wright, M. A.↗
Jet to freestream velocity ratio computations for a jet in a crossflow
The flowfield induced by a single, subsonic jet exhausting perpendicularly from a flat plate into a subsonic crossflow has been numerically investigated. Time-averaged solutions were obtained using the thin-layer Navier-Stokes equations and two overlapping grids. Test cases were chosen to match available experimental data where the jet Mach number was 0.78 and the freestream Mach number was varied to represent effective velocity ratios R from 4 to 12. Comparisons of the pressures induced on the flat plate are presented. The results show that the best agreement is obtained for R of 4 and 6, R of 8 is more difficult to resolve, and the R of 12 solution was not satisfactory. It is anticipated that the resolution could be improved by using either smaller time steps or finer grid spacing as R increases.
Margason, Richard J.↗
Influence of internally generated pure tones on the broadband noise radiated from a jet
An experimental study was conducted to determine subsonic-jet-noise amplification by plane waves of sound (pure tones) generated upstream of the nozzle over wide ranges of frequency and amplitude. The data were used to evaluate the behavior of the pure tone and the broadband parts of the radiated sound in the far field. It is shown that a significant increase of broadband noise occurs only when the amplitude of the tone in the far field exceeds the sound pressure of the broadband noise at the same location in the far field. Therefore, the sensitivity of the jet to the pure-tone excitation is not large.
Parthasarathy, S. P.↗
Quasi-periodic structure of a turbulent jet
The instantaneous near field pressure fluctuations of an axisymmetric subsonic jet were measured by using a longitudinal and an azimuthal microphone arrays in order to qualitatively determine the behaviors of the quasi-periodic structure within the flow. Statistical analysis is used to explain the characteristic of the pressure signals. In addition to the information obtained by forming the power spectral density, auto- and cross-correlation functions, two types of signals are extracted through a conditional probability analysis to represent the quasi-periodic and the random fine structures within the turbulent jet. The quasi-periodic structure first appears as a rolling up of the mixing layer flow within one nozzle diameter downstream of the exit, then becomes fully developed at approximately 3 nozzle diameters downstream with a preferred Strouhal number range 0.3-0.4, and finally disappears beyond the end of potential core. This behavior is also reflected in the variation of the convection velocity.
Maestrello, L.↗
Distributed Exhaust Nozzles for Jet Noise Reduction
The main objective of this study is to validate the jet noise reduction potential of a concept associated with distributed exhaust nozzles. Under this concept the propulsive thrust is generated by a larger number of discrete plumes issuing from an array of small or mini-nozzles. The potential of noise reduction of this concept stems from the fact that a large number of small jets will produce very high frequency noise and also, if spaced suitably, they will coalesce at a smaller velocity to produce low amplitude, low frequency noise. This is accomplished through detailed acoustic and fluid measurements along with a Computational Fluidic Dynamic (CFD) solution of the mean (DE) Distributed Exhaust nozzle flowfield performed by Northrop-Grumman. The acoustic performance is quantified in an anechoic chamber. Farfield acoustic data is acquired for a DE nozzle as well as a round nozzle of the same area. Both these types of nozzles are assessed numerically using Computational Fluid Dynamic (CFD) techniques. The CFD analysis ensures that both nozzles issued the same amount of airflow for a given nozzle pressure ratio. Data at a variety of nozzle pressure ratios are acquired at a range of polar and azimuthal angles. Flow visualization of the DE nozzle is used to assess the fluid dynamics of the small jet interactions. Results show that at high subsonic jet velocities, the DE nozzle shifts its frequency of peak amplitude to a higher frequency relative to a round nozzle of equivalent area (from a S(sub tD) = 0.24 to 1. 3). Furthermore, the DE nozzle shows reduced sound pressure levels (as much as 4 - 8 dB) in the low frequency part of the spectrum (less than S(sub tD) = 0.24 ) compared to the round nozzle. At supersonic jet velocities, the DE nozzle does not exhibit the jet screech and the shock-associated broadband noise is reduced by as much as 12 dB.
Ahuja, K. K.↗
Subsonic and supersonic jet flow and acoustic characteristics and supersonic suppressors
To study the similarities and differences between subsonic and supersonic jets, velocity and impact pressure fluctuations were determined along the axis over a jet Mach number range of 0.6 to 1.4 for a 2 in. diameter convergent nozzle and for a one inch diameter jet flow. Static pressure distribution fluctuations due to shear and turbulence in the jet flow for subsonic and supersonic jets were related to acoustic radiation to the far field. Also determined were flow and acoustic characteristics of a single shroud, and multiple shroud tube and shroud suppressors for supersonic and subsonic exhaust velocities. A compressor consisting of 191 tubes and 191 shrouds decreased the primary Mach number drastically for both jet Mach numbers of 1.4 and 0.7; rms impact and static pressure fluctuations on the axis were also reduced from values existing for an equivalent area single nozzle.
Nagamatsu, H. T.↗