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At least 55 records · Page 3

The Spectacular Radio-Near-IR-X-Ray Jet of 3C 111: the X-Ray Emission Mechanism and Jet Kinematics

Relativistic jets are the most energetic manifestation of the active galactic nucleus (AGN) phenomenon. AGN jets are observed from the radio through gamma-rays and carry copious amounts of matter and energy from the subparsec central regions out to the kiloparsec and often megaparsec scale galaxy and cluster environs. While most spatially resolved jets are seen in the radio, an increasing number have been discovered to emit in the optical/near- IR and/or X-ray bands. Here we discuss a spectacular example of this class, the 3C 111 jet, housed in one of the nearest, double-lobed FR II radio galaxies known. We discuss new, deep Chandra and Hubble Space Telescope (HST) observations that reveal both near-IR and X-ray emission from several components of the 3C 111 jet, as well as both the northern and southern hotspots. Important differences are seen between the morphologies in the radio, X-ray, and near-IR bands. The long (over 100 kpc on each side), straight nature of this jet makes it an excellent prototype for future, deep observations, as it is one of the longest such features seen in the radio, near-IR/optical, and X-ray bands. Several independent lines of evidence, including the X-ray and broadband spectral shape as well as the implied velocity of the approaching hotspot, lead us to strongly disfavor the EC/CMB model and instead favor a two-component synchrotron model to explain the observed X-ray emission for several jet components. Future observations with NuSTAR, HST, and Chandra will allow us to further constrain the emission mechanisms.

galaxies: active – galaxies: jets – radio cont↗

The structure of jet turbulence producing jet noise.

Measurements are presented that characterize the structure of the jet in both the core and the surrounding annular mixing region. Experiments were carried out in a 1.5-inch diameter subsonic jet at Mach numbers of 0.3, 0.5, and 0.7. The growth of pressure fluctuations within the core from the jet outlet to the end of the jet core was traced through the examination of spectral results. The spectra in the jet core exhibited a peak whose frequency scaled with the jet velocity and the jet diameter which is related to a characteristic dimension of the mixing process. A digital data reduction program was used to calculate the auto- and cross-correlations of axial velocity fluctuations. In the core the cross-correlations were nearly constant in the space-time plane indicating a traveling pressure wave, while in the annular mixing region the cross-correlations exhibited the usual decay in the space-time plane characteristic of convected turbulence.

Wooldridge, C. E.↗

Design and experimental results for a turbine with jet flap stator and jet flap

The overall performance and detailed stator performance of a negative hub reaction turbine design featuring a moderately low solidity jet flap stator and a jet flap rotor were determined. Testing was conducted over a range of turbine expansion ratios at design speed. At each expansion ratio, the stator jet flow and rotor jet flow ranged up to about 7 and 8 percent, respectively, of the turbine inlet flow. The performance of the jet flap stator/jet flap rotor turbine was compared with that of a turbine which used the same jet flap rotor and a conventional, high solidity plan stator. The effect on performance of increased axial spacing between the jet stator and rotor was also investigated.

Bettner, J. L.↗

Jet noise suppression by swirling the jet flow.

The effect of swirling flow on jet noise suppression was experimentally investigated in a relatively small, low-thrust, fan-jet engine. Measurements of acoustic properties of the near and far fields, jet-flow characteristics, and engine thrust were made with and without stationary swirl vanes installed in the primary exhaust nozzle. Preliminary test results indicate that substantial reductions in jet overall sound pressure levels and overall acoustic power were obtained with minimal thrust losses. Based on preliminary analysis, present results, and previous experiments with swirling hot jets, it is predicted that even greater jet noise reductions can be obtained in higher thrust engines, particularly with afterburning, by swirling jet exhaust.

Schwartz, I. R.↗

Use of cross-correlation measurements to investigate noise generating regions of a real jet engine and a model jet

Cross-correlations are reported of the jet static pressure fluctuations (as measured with a B and K microphone fitted with a nose cone), with the far-field radiated sound pressure. These measurements were made for various probe positions and a large number of far-field positions (at various angles). In addition, the tests were run for a number of different jet exit velocities. The measured, normalized cross-correlation functions vary between 0.004 and 0.155. These values depend upon the angular position of the far-field microphone, the jet exit Mach number, and the position of the probe. In addition, the cross-correlation technique was employed to study the symmetry of the far-field radiated sound about the jet axis. Third-octave analyses of both the probe signal and the far-field radiated sound were made. This is the first time correlation measurements have been made on a jet engine. In addition, a report is given on an extensive noise survey of a model jet. The correlations are related to sound source functions and jet source regions are discussed.

Meecham, W. C.↗

Velocity field of a round jet in a cross flow for various jet injection angles and velocity ratios

A subsonic round jet injected from a flat plate into a subsonic crosswind of the same temperature was investigated. Velocity and pressure measurements in planes perpendicular to the path of the jet were made for nominal jet injection angles of 45 deg, 60 deg, 75 deg, 90 deg, and 105 deg and for jet/cross flow velocity ratios of four and eight. The velocity measurements were obtained to infer the properties of the vortex pair associated with a jet in a cross flow. Jet centerline and vortex trajectories were determined and fit with an empirical equation that includes the effects of jet injection angle, jet core length, and jet/cross flow velocity ratios.

Fearn, R. L.↗

Development and structure of a rectangular jet in a multiple jet configuration

Results of hot-wire measurements in an incompressible jet issuing from an array of rectangular lobes, equally spaced with their small dimensions in a line, are presented. The quantities measured include mean velocity and the Reynolds stress in the two central planes of the jet at stations covering up to 115 widths (small dimension of the lobe) downstream of the nozzle exit. Measurements are carried out on a single rectangular free jet and on the same jet in a multiple jet configuration. In the case of a multiple jet, the flowfield for downstream distance X greater than 60D (D = width of the lobe) resembles that of a jet exiting from a two-dimensional nozzle with its short dimension being the long dimension of the lobe. The field of turbulence is found to be nearly isotropic in the plane containing the small dimension of the lobes for X greater than 60D.

Krothapalli, A.↗

Jet decay rate effects on hover jet-induced loads

The paper explains the mechanisms for observed jet decay rate effects on jet-induced loads on a flat plate for cross-flow and hover configurations. Examples are presented for the influence of the decay rate on integrated loads on a flat plate induced by the jet issuing at a right angle from the plate into still air; knowledge of these jet-induced loadings is of particular importance for VTOL aircraft design because they produce an effective loss in the lift force available in hover. The apparent inconsistency between existing lift loss vs jet decay rate trends is explained in light of the different mechanism which determine the jet mixing and trajectory, i.e., entrainment, blockage, and the vortex pair associated with a jet in crossflow.

Kuhlman, J. M.↗

A study of real jet effects on the surface pressure distribution induced by a jet in a crossflow

A study of jet exit profile, exit Mach number, swirl and turbulence level on jet-induced loadings for jets exhausting from a surface into a crossflow is presented. The importance of each of these real jet characteristics is assessed using available data. Where adequate surface pressure distribution data are available, a correlation method to predict surface pressure for a jet exhausting from an infinite flat plate is used either to attempt to develop a correlation based on the real jet characteristics or to model the effects of that characteristic. Data comparisons are presented for selected cases. Also, a summary of information on surface pressure distribution data for jet exhausting from flat plates into a subsonic crossflow is presented.

Perkins, S. C., Jr.↗

Jet trajectories and surface pressures induced on a body of revolution with various dual jet configurations

A jet in a cross flow is of interest in practical situations including jet-powered VTOL aircraft. Three aspects of the problem have received little prior study. First is the effect of the angle of the jet to the crossflow. Second is the performance of dual-jet configurations. The third item for further study is a jet injected from a body of revolution as opposed to a flat plate. The Test Plan for this work was designed to address these three aspects. The experiments were conducted in the 7 x 10 tunnel at NASA Ames at velocities 14.5 - 35.8 m/sec (47.6 - 117.4 ft/sec). Detailed pressure distributions are presented for single and dual jets over a range of velocity ratios from 3 to 8, spacings from 2 to 6 diameters and injection angles of 90, 75 and 60 degrees. Some flowfield measurements are also presented, and it is shown that a simple analysis is capable of predicting the trajectories of the jets.

Schetz, J. A.↗

Modified jet noise source model for twin-jet shielding analysis

An analytical method to estimate the influence that a jet of heated flow has on the noise emission from a parallel jet is presented. The shielding jet is modelled as a cylinder of constant cross-section in which the flow speed and temperature are uniform throughout. The jet noise emission is modelled by a point source with directivity imposed. The directivity term consists of: a self-noise term, a shear-noise term, and a convection factor. The self- and shear-noise terms each contain a basic directivity factor multiplying a spectral shape function. The various components are evaluated based on comparison with isothermal jet radiation experimental data. The modified source term is incorporated into the jet shielding model and compared to heated twin jet shielding data. The estimated spectra agree well except further downstream of the nozzle where peak of the noise spectrum estimated by the model lies approximately one octave below the experimental peak. The noise reduction estimated by the model agrees favorably with experiment in the near downstream region. This discrepancy is explained in terms of the shielding mechanism which is dominant far downstream.

Gerhold, C. H.↗

Supersonic gasdispersional jets and jet noise

This paper examines the potential for controlling jet noise radiation using methods developed for modifying jet infra-red thermal radiation. The control of jet noise may be possible by properly adding different solid and liquid particles into the jet flow and by using special nozzle shapes to change the jet exhaust flow structure. The numerical methods used to achieve these objectives are outlined in this paper. A combined Lagrangian-Eulerian approach is used to numerically simulate a Jet flow with particle addition. The unsteady behavior of jet impingement is examined. The techniques for grid and boundary condition definition are discussed as related to the accuracy of the calculations. Preliminary comparisons to experimental data are presented.

Gilinsky, M. M.↗

Effect of Ratio of Jet Area to Total Area and of Pressure Ratio on Lift Augmentation of Annular Jets in Ground Effect Under Static Conditions

The present investigation was undertaken to determine the effects of the ratio of jet area to total area and of the pressure ratio on the lift-augmentation characteristics of annular jets in ground effect. The investigation was made over an area-ratio range of 1.00 to 0.02 and a pressure-ratio range of about 1.04 to 1.95. Several configurations with center jets were tested through an angle-of-attack range to determine the pitching-moment characteristics. The tests were conducted in a static test room with the use of the compressed-air facilities. The results show that lift augmentation increases somewhat as the area ratio is reduced to about 0.10, below which it deteriorates due to thin jet mixing. The effect of pressure ratio on lift was negligible for the area-ratio range investigated. Calculations of the lift per air horsepower for a given base loading indicate that the greatest lift per air horsepower occurs at area ratios above 0.10, where the greatest lift augmentation occurs. The data show that annular-Jet vehicles are unstable at ratios of height above ground to nozzle diameter above about 0.10. The stability of the annular-jet vehicle can be improved by the use of large center jets. Base compartments also reduces the unstable moment.

Goodson, Kenneth W.↗

Spreading of Exhaust Jet from 16 Inch Ream Jet at Mach Number 2.0 / Fred Wilcox, Donald Pennington

An investigation of the jet-spreading characteristics of a 16 inch ram-jet engine was conducted in the 8 by 6 foot supersonic tunnel at a Mach number of 2.0; both a converging nozzle having a contraction ratio of 0.71 and a cylindrical extension to the combustion chamber were used. The jet boundaries determined by means of pitot pressure surveys were compared with boundaries calculated from one-dimensional continuity and momentum relations. For the cylindrical nozzle, the jet reaches its maximum diameter, 4 percent greater than calculated, about 0.6 nozzle-exit diameter downstream of the nozzle exit. The maximum diameter for the converging nozzle was 7 percent greater than calculated from one dimensional relations and occurred from 1 to 1.5 nozzle-exit diameters downstream of the exit. Non dimensional maximum jet diameters agreed closely with results of an investigation by Rousso and Baughman; these data were obtained with low-temperature jets exhausting into a stream at a Mach number of 1.91 from nozzles having exit diameters of 0.75 inch.

INTERFERENCE, JET-MISSILES↗

Fundamentals of the Control of Gas-Turbine Power Plants for Aircraft: Principles of Control Common to Jet, Turbine-Propeller Jet, and Ducted-Fan Jet Power Plants - Part 2

After defining the aims and requirements to be set for a control system of gas-turbine power plants for aircraft, the report will deal with devices that prevent the quantity of fuel supplied per unit of time from exceeding the value permissible at a given moment. The general principles of the actuation of the adjustable parts of the power plant are also discussed.

Kuehl, H.↗

Secondary jet interaction with emphasis on outflow and jet location.

Data were obtained concerning a model which utilized a two-dimensional sonic jet. It was found that outflow and jet location significantly influence the magnitude and behavior of the secondary jet interaction forces. Continued refinements in jet interaction analyses which do not account for outflow are of limited usefulness in the design of control systems for supersonic and hypersonic vehicles. The jet total back pressure ratio increases with either jet pressure ratio or freestream Mach number.

Hefner, J. N.↗

Investigation of the large scale coherent structure in a jet and its relevance to jet noise

A study was conducted to determine the causes of aircraft noise in large jet aircraft. It was determined that jet noise varies strongly with velocity and that significant pure tones are generated by rotor-stator interaction in the jet engines. An objective method for deducing the large eddy structure in a large jet is described. The provisions of lighthill's theory are analyzed and applied to investigating the nature of jet noise. There is considerable evidence that a large scale coherent structure exists in a jet and that this structure can play a major role in sound radiation. Mathematical models are developed to define the parameters of orthogonal decomposition, finite extent velocity field, homogeneous fields, and periodic velocity fields.

Arndt, R. E. A.↗