Jet Precession Research Articles

Precessing jet burners for stable and low NO x pulverised fuel flames — preliminary results from small-scale trials

A new technique for stabilising pulverised coal flames for rotary kilns was demonstrated at 150 kW scale in a model kiln using a burner consisting of a central precessing air jet nozzle and an outer annular coal transport channel. Effective flame stabilisation was achieved by the influence of the precessing air jet on particle trajectories resulting in a reduction in ignition distance by a factor of three compared to a mono-channel burner. A corresponding reduction in CO emissions from 810 to 190 ppm (0% O 2 basis) and an increase in carbon burnout from 84 to 92% were achieved without any increase in NO x emissions, which were in the region of 85–100 ppm (0% O 2).

Velocity measurements in a precessing jet flow using a three dimensional LDA system

The turbulent, three dimensional and time dependent flow field of a precessing jet is investigated. In the present case the jet precession is generated by mechanically rotating a round jet inclined relative to the axis of rotation. A conditional flow visualisation technique is used to complement three dimensional laser Doppler velocity data, time-averaged and phase-averaged at the frequency of precession. The conditional phase-averaging technique enables phase-averaged velocity contours and vectors to be obtained which reveal flow patterns and structures within the flow field. Time-averaging of the velocity data shows that these structures are significant in that they generate a reverse flow (recirculation) region between the jet and its spinning axis. They are found also to cause a rapid decay of the mean velocity. The characteristics of the precessing jet found here are compared with previous investigations of the same flow and with investigations of other turbulent jets.

Laboratory experiments of a jet impinging on a stratified interface

The entrainment rates of vertical and inclined jets impinging on a stratified interface are measured in water tank experiments. At moderate Richardson number, the entrainment rate of the vertical jet is proportional to Ri-1/2, independent of Reynolds number. The inclined jets are tilted at 15° from the vertical. In one case, the jet nozzle is rotated about a vertical axis, so that the inclined jet precesses, while in the other, it is stationary. The inclined jets entrain at a rate proportional to Ri-3/2, whether precessing or not. This behavior is consistent with a new model of stratified entrainment which accounts for vortex persistence.

Signatures of helical jets

Observational signatures of helical jets can be found in some X-ray binaries (XRB), planetary nebulae, Herbig-Haro objects and in jets of active galactic nuclei (AGN). For example, in the XRB SS433 a kinematic model of precessing jets has been applied very successfully and yielded a determination of its distance which is independent of conventional methods. In galactic jets precession appears to be the predominant mechanism for the production of observed helical signatures. In extra-galactic jets other mechanisms seem to be similarly frequent. As a result of their strong dependence on the direction of motion with respect to the observer, special relativistic effects can be pronounced in helical jets. These have to be taken into account in AGN-jets and the newly discovered galactic sources which show apparent superluminal motion. Since the galactic superluminal jets are located in a binary system, jet precession is very likely in these sources. In this paper I review the main structural and kinematic signatures of helical jets and briefly mention the physical mechanisms behind them. I will present kinematic simulations of relativistic jets which are helically bent or have an internal helical flow field.

The tidally induced warping, precession and truncation of accretion discs in binary systems: three-dimensional simulations

We present the results of non-linear, hydrodynamic simulations, in three dimensions, of the tidal perturbation of accretion discs in binary systems where the orbit is circular and not necessarily coplanar with the disc mid-plane. The accretion discs are assumed to be geometrically thin, and of low mass relative to the stellar mass so that they are governed by thermal pressure and viscosity, but not self-gravity. The parameters that we consider in our models are the ratio of the orbital distance to the disc radius, D/R, the binary mass ratio, Ms/Mp, the initial inclination angle between the orbit and disc planes, δ, and the Mach number in the outer parts of the unperturbed disc, ℳ. Since we consider non-self-gravitating discs, these calculations are relevant to protostellar binaries with separations below a few hundred au. For binary mass ratios of around unity and D/R in the range 3 to 4, we find that the global evolution of the discs is governed primarily by the value of ℳ. For relatively low Mach numbers (i.e. ℳ = 10 to 20) we find that the discs develop a mildly warped structure, are tidally truncated, and undergo a near rigid body precession at a rate which is in close agreement with analytical arguments. For higher Mach numbers (ℳ ≈ 30), the evolution is towards a considerably more warped structure, but the disc none the less maintains itself as a long-lived, coherent entity. A further increase in Mach number to ℳ = 50 leads to a dramatic disruption of the disc as a result of differential precession, since the sound speed is too low to allow efficient communication between constituent parts of the disc. Additionally, it is found that the inclination angle between the disc and the orbital angular momentum vectors evolves on a longer time-scale, which is probably the viscous evolution time-scale of the disc. The calculations are relevant to a number of observed astrophysical phenomena, including the precession of jets associated with young stars, the high spectral index of some T Tauri stars, and the light curves of X-ray binaries such as Hercules X-1 which suggest the presence of precessing accretion discs.

The Influence of Fuel Jet Precession on the Global Properties and Emissions of Unconfined Turbulent Flames

Abstract An investigation was conducted to characterize the shape and size, the global radiation, and the CO and NOx, emissions of precessing jet flames and to compare these results with conventional, free, turbulent jet diffusion flames. Jet precession was accomplished using a mechanically-rotated nozzle. Parameters varied include nozzle diameter, jet deflection angle, initial jet velocity (Reynolds number), dimensionless precession frequency (Strouhal number), and fuel type. Measured quantities included visible flame dimensions; NOx, NO2, and CO emissions; and radiant heat flux. Results of these experiments showed that two broad regimes of flame type exist for precessing jet flames. For precession Strouhal numbers (St p ) less than about 0.01, flames are non-luminous and, in comparison with conventional flames, are short and broad. For St p > 0.03, flames are highly luminous, and of a shape which is between that of a conventional jet flame and the low-St p flame. In general, radiant fractions increase w...

Possible Evidence for a Binary Massive Black Hole in the Galactic Nucleus

The Galactic Centre candidate Sgr A∗ may exhibit a 40 km/s radial velocity component, which is not observed for OH/IR stars around the centre. This could be interpreted as orbital motion of one member of a binary massive black hole. In other galaxies such pairs may be inferred from radio jet precession and emission line profiles.

Precessing Gamma jets, GRB and the twin rings around SN1987A

Gamma jets (GJ) at MeV energies may be produced in galactic halos by Inverse Compton Scattering (ICS) of collinear ultrarelativistic electron beams (at GeV energies) onto thermal photons. These electron jets are emitted by neutron star jets (NSJ) or black holes (BH) while the target thermal photons are generated by a nearby binary stellarlike companion (or by a relic accreting disk). The GJ precesses in a conical shape as a lighthouse (with a characteristic Keplerian binary period) forced by the NSJ magnetic lines interaction with the stellar companion ones. The sudden blazing of the GJ, once the observer is into the beam cone direction, is detected as a GRB. Our predicted GRB spectra fit the GRB observed ones; GRB luminosity, variability and counts are well explained if the GJ sources are located in an ”extended” and an ”evaporating” galactic halo as the one recently required in the fast running away NS model. Observed jets such as SS433, the Great Annihilator, superluminal sources such as the last GRS1758-258, GRS1915+105 are the ideal candidates for NSJ as well as GJ. The SGRs are the lower energy and wider beamed version of this GJ model so they are linked to classical GRBs. The last mysterious presence of the twin rings near SN1987A (as well as the ring traces near NGC6543) are the spectacular signature of such (double sided) conical jet precession projected onto the red giant relic spherical shell. The tiny but very puzzling offaxis nature of the SN1987A twin rings is due to the high eccentricity of the binary NSJ. The GRBs from the nearby Andromeda halo might be detected as soon as the instrumental sensitivity is increased.

A parsec-scale 'superjet' and quasi-periodic structure in the HH 34 outflow?

view Abstract Citations (138) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Parsec-Scale ``Superjet'' and Quasi-periodic Structure in the HH 34 Outflow? Bally, John ; Devine, David Abstract We report the detection of a new Herbig-Haro (HH) object, HH 173, near the young stellar object HH 34* in the L1641 molecular cloud in Orion. The new object appears to be part of a remarkable bipolar chain that includes known HH objects in this region and extends symmetrically about HH 34* for 1.5 pc. The chain terminates in the north at the position of HH 33 and includes HH 40, HH 85, HH 126, and HH 34N. Toward the south, the chain ends at the position of HH 88 and includes HH 87, HH 86, HH 173, HH 34X, HH 34, and the HH 34 jet. All HH objects in the chain that have recognizable bow shock morphologies point to a driving source in the HH 34* cloud core. We propose that this chain delineates a 3 pc long bipolar outflow from HH 34* with blueshifted gas in the south and redshifted gas in the north. The quasi-periodic spacing of the HH objects may be a consequence of episodic mass-loss events from HH 34* occurring roughly every 900/V300 yr (for a flow velocity V300 measured in units of 300 km/sec). The dynamic age of the most distant HH object from HH 34* is approximately 5000 yr. The S-shaped symmetry of the HH objects about the central source may result from jet precession with a period of approximately 104 yr. Publication: The Astrophysical Journal Pub Date: June 1994 DOI: 10.1086/187394 Bibcode: 1994ApJ...428L..65B Keywords: Astronomical Models; Bipolarity; Ejecta; Herbig-Haro Objects; Outlet Flow; Periodic Variations; Star Formation; Stellar Mass Ejection; Stellar Structure; Cassegrain Optics; Charge Coupled Devices; Data Acquisition; Data Reduction; Images; Optical Filters; Telescopes; Astrophysics; ISM: JETS AND OUTFLOWS; STARS: FORMATION; STARS: PRE--MAIN-SEQUENCE; STARS: INDIVIDUAL ALPHANUMERIC: HH 34 * full text sources ADS | data products SIMBAD (24)

Hydrodynamic Collimation of Precessing Jets

Numerical experiments of a precessing adiabatic jet similar to SS 433 are presented which display hydrodynamic collimation on a large scale as suggested by an earlier work (Eichler 1983). The differences between this work and that of Kochanel & Hawley (1990), who argued against hydrodynamic collimation, are explained

α-Disks and the precession of extragalactic jets

This paper considers a mechanism in which a black hole is driven to precess by a surrounding accretion disk, and points out the dependence of the precession period on the accretion rate. The result is in good agreement with the observational data of extragalactic jets.

Reduced NO x emissions and enhanced large scale turbulence from a precessing jet burner

The performance characteristics of a Precessing Jet (PJ) burner, developed at the University of Adelaide, have been investigated in Furnace No. 1 of the International Flame Research Foundation firing natural gas with air pre-heated to 320°C. Results showed that the PJ burner, operating without air swirl, fuel staging or FGR, produces NOx emissions of about 57 ppm (dry, 3% O2) which is comparable to the performance of a swirled flame operated at optimised conditions with either flue gas recirculation, FGR, or fuel staging. The emissions are significantly lower than the 134 ppm measured for the base-line swirl burner, but greater than the 37 ppm measured for the swirl burner operated with both FGR and fuel staging. The flame was investigated by means of in-flame measurement of temperature and species concentration using suction probes and by laser sheet visualisation and subsequently derived probability density functions of jet fluid concentration. These techniques show that the mixing and combustion processes are dominated by the presence of large scale structures. It is anticipated that a more complete understanding of the interaction between the large scale turbulence and the combustion process will lead to further improvements in the performance of the burner.

Random Precessing Jet and Accretion Disk at the Galactic Center

As a mechanism to generate asymmetric radio features in the central 50 pc of the Galaxy (Sofue and Fujimoto 1987), we consider a gaseous jet from the tilted accretion disk at the center and the interaction of the jet with ambient gas on the galactic plane. It is shown schematically in figure 1 that the magnetic torques N1,2,3 exert on a gaseous element ρhΔsΔr of a ring to change its tilted orbital plane, and where γ1,2,3 are constants of a factor of unity and e1,2,3 unit vectors. The azimuthal angle ϕ is measured along the rotation from the lowest part of the ring below the galactic plane. The orbital plane is tilted against the galactic plane by the angle θ The change of the angular momentum of the disk element L = ρhΔsΔrr × v is, where 〈〉 means the average over one rotation period T or over ϕ = 0 to 2π in equations (1) to (3).

Collimated nuclear ejection of radio-emitting plasma in the Seyfert galaxy NGC 4388

New 6 cm and 20 cm continuum VLA maps of the edge-on Seyfert galaxy NGC 4388 are presented. These observations reveal a double-peaked radio source close to (but not coincident with) the optical Seyfert nucleus. Additionally, a cloud of radio-emitting material, apparently ejected from the nucleus, extends beyond the double-peaked source into the halo of the galaxy. The radio spectra indicate nonthermal emission. Mid-infrared observations reveal that the 10 micron source is displaced from the optical nucleus in a direction similar to that in which the radio emission is displaced. The overall radio structure is bent, with the outer structure aligning roughly perpendicular to the galaxy disk. It is suggested that either gravitational buoyancy, jet precession, or a combination thereof are responsible for this radio morphology. 31 references.

Precessing radio jets in AGNs

Conditions that may lead to jet precession as well as extragalactic radio sources that can be interpreted as such are reviewed. Attempts to calculate model brightness distributions for these and some related sources are discussed, with specific attention for “preferential avoidance” patterns and one-sided jets. Subsequently several conceivable applications of observations of jet precession are described.

Are Bipolar Jets Precessing?

No one has drawn attention as to whether bipolar jets precess or not. We examine here the possibility of precession of bipolar jets from a theoretical point of view (Fukue and Yokoo 1986).We first characterize various models proposed for bipolar jets in the light of precession. That is, can they admit precession? If they can, how long is a precessional period P?

Are bipolar jets precessing?

Whether bipolar jets from the star-forming regions precess or not is indicative of their model of origin and formation. Both the beam model1 and the model of the shocked interaction between an isotropic stellar wind and a massive isothermal disk2,3 have difficulty in explaining this precession. Other models4–7, which admit precession of jets, predict different periods of precession. If the recent observation of L723 (ref. 8) represents precession, then this is probably the orbital precession of a torus (disk) around a central oblate star, or the forced precession of a torus around a central star by its companion. The free precession of a central star as well as the precession of a torus may be responsible in the case of L1551 IRS5 (refs 9–11).

Supermassive binaries in active galactic nuclei

Recent observational evidence1–6 indicating the apparent precession of jets in compact and extended radio sources suggests the presence of a second massive body in the nuclei of the associated active galaxies7 (we include quasars as active nuclei). On the basis of their similarities with close binaries in the Galaxy, two of which (SS433 and Her X-1) are known to contain precessing beams and disks, we consider here the possibility that the secondary object is a Roche overflowing supermassive star (SMS) of mass M2∼106−108M⊙ in orbit around a primary massive black hole (MBH) of mass M1∼107−109M⊙.

Structure, strength, and polarization changes in radio source SS433

VLA observations of SS433 at 1,465, 4,885, and 15,035 MHz between 8 September 1979 and 20 June 1980 show structure with size scales between 0.1 and 5 arc s which changes significantly on time scales of 1–2 weeks. Jets with 8–20% linear polarization are ejected on both sides of the central radio source which is coincident with the optical image, along position angles between 80° and 120° with a mean position angle for ejected material of 100°. Features in linear polarized intensity maps can be identified in four successive epochs spanning 196 days, and the resulting proper motions for identifiable clouds are 0.0088 arc s per day. If the feature velocities are equal to that of the optical emission lines, the distance to SS433 is 5.1 kpc. The position angles of identifiable features correlate well with the known precessing optical jets if one extrapolates back to the time of ejection using the observed transverse speeds. The equipartition magnetic field strengths of 0.001–0.01 G indicate synchrotron lifetimes of 109–1011 s; therefore synchrotron losses are not a dominant factor in the evolution of the extended radio emission. The evolution of radio jets indicates that the relativistic electrons and magnetic fields seen as synchrotron emission may be generated by flows along the rotation axis of the accretion disk of the SS433 star system.