Jet Source Research Articles

Isothermal and heated subsonic jet noise using large eddy simulations on unstructured grids

Jet noise remains the major contributor to airplane noise at take-off. In the past half-century of research, sound generation mechanisms in supersonic jets have been extensively characterized, while the sound sources in subsonic jets are still to be clearly identified. For the last two decades, Large Eddy Simulations (LES) have become a major tool for investigating jet noise sources due to their ability to capture detailed information in turbulent flows and their moderate cost that allows industrial applications. However, many challenges still arise when dealing with complex nozzle geometries and heating effects in the jet core. In this paper, subsonic jets with or without nozzle geometry at Mach number of 0.9 and moderately high Reynolds numbers ranging from 2 × 105 to 1 × 106 are computed using LES, providing a base of validation for different nozzle configurations and operating conditions. In this work, the high-order unstructured LES solver AVBP is combined with Ffowcs Williams and Hawkings’ acoustic analogy on unstructured grids. The vortex pairing phenomenon is evidenced without properly triggering the turbulence in the jet at the nozzle exit. Hence, a non-geometrical tripping, where the firsts prism layers of the mesh at the nozzle wall are removed, is proposed and shown to be a successful method for triggering proper turbulence development in shear layers for the cases with nozzle. Moreover, it is more easily implemented because it does not require any geometrical modifications and it generates more natural turbulence than previous methods, leading the path to actual industrial dual-stream configurations. Both isothermal and heated jet flow cases are performed and validated with existing experimental data in terms of aerodynamics and acoustics, which demonstrates the capacity of an unstructured LES solver to correctly simulate both cold and heated jet noise phenomena.

Plasma jet cleaning of optics

SummaryOptical components used in normal ambient conditions are usually contaminated by hydrocarbons from the ambient air in the course of time. This contamination gives rise to a decrease in the particular optical performance, i.e. the reflectance of mirrors or the transmittance of lenses and windows. In order to address this issue, the impact of ageing at ambient conditions as well as subsequent plasma cleaning on relevant parameters of standard silver‐coated mirrors was investigated in this work. For plasma cleaning, a jet source based on a dielectric barrier discharge at atmospheric pressure was applied. It is shown that ageing leads to an adhesion of carbonaceous contaminations and an accompanying decrease in reflectance of the mirrors. The subsequent plasma cleaning process allows the efficient removal of surface‐adherent carbon and an alteration of remaining bonds. Finally, this effect gives rise to an increase in reflectance, nearly restoring the initial value before ageing.

Application of dual radio frequency inductive coupled plasma into CVD diamond growth

Diamond films have been deposited by a tandem type of radio frequency inductive coupled plasma jet source with the maximum deposition time of 150 h. The morphology, impurity and crystal structure of the deposited films were characterized. By controlling the feed gas composition, nano- and micro-crystal diamond films were deposited on silicon substrates without any metal impurity detected, and the single crystal diamond film was deposited on a diamond substrate with regular crystal lattice structure. Plasma diagnosed by optical emission spectra revealed that this plasma jet source possessed of the high values of the electron temperature (averaged at 2.2eV) and the plasma density (averaged at 4.0 × 1016/cm3), as well as the stable plasma composition fitting for the diamond growth.

Development of the Strategy of Active Control of Instability Waves in Unexcited Turbulent Jets

The possibility of controlling instability waves in the mixing layer of a subsonic unexcited jet is studied. These waves can be noise sources in both free jets and jets as parts of configurations. In the study the method of experimental diagnostics of the instability waves in the near field of a jet using an azimuthal multimicrophone array is realized. The data on the near field fluctuations are used for testing the control strategy proposed by the authors. The strategy consists in narrowband sliding filtration of the original signal and the formation of a narrowband controlling action on the basis of the linear principle of signal superposition. The results of the study represent the next step toward the realization of an active control system suppressing natural instability waves in turbulent jets.

A precessing and nutating jet in OJ287

AbstractWe re-analyzed OJ287 in 120 Very Long Baseline Array (VLBA, MOJAVE) observations (at 15 GHz) covering the time span between Apr. 1995 and Apr. 2017. We find that the radio jet motion over the sky is consistent with a precessing and nutating jet source. The variability of the radio flux-density can be explained by Doppler beaming due to a change in the viewing angle. We suggest that part of the optical emission is due to synchrotron emission related to the jet radiation. We find a strikingly similar scaling for the timescales for precession and nutation as indicated for SS433 with a factor of roughly 50 times longer in OJ287.

Development, validation and application of a newly developed rig facility for investigation of jet aeroacoustics

Over the last decades, significant improvements have been achieved in terms of noise reduction for jet engine aircraft. Nevertheless, jet noise remains one of the major sound sources from commercial aircraft, particularly during take-off. To develop strategies for jet noise reduction, it becomes paramount to understand the mechanisms of sound production and radiation from the experimental point of view. For this reason, researchers need high-quality noise data, obtained under proper conditions for both the acoustic and flow fields of scaled jets. This paper reports the development, validation and application of a new jet rig facility built at Federal University of Santa Catarina for investigations of jet noise. Issues relating to limited budget, deadline fulfillment and inner space restrictions, made the design and construction of the facility particularly difficult. Such drawbacks were overcome by designing carefully every system making up the whole facility, some of them based on CFD analyses, as well as by employing tailored solutions to some systems. Throughout the paper, the infrastructure of facility and its main systems are presented as well as major design requirements are discussed. Subsequently, the free-field qualification and the determination of acoustic far-field for the jet source, concerning the anechoic chamber, are described. With the aim of evaluating the acoustic performance of the facility, noise data were acquired for jet flows with Mach numbers from 0.3 to 0.9 and observer locations from 60 to 150 degrees. Additionally, hot-wire anemometry measurements were performed at different axial positions along the jet to illustrate the turbulent character of flows generated. Results of flow and noise measurements revealed an acoustically clean signature as well as turbulence properties in good agreement with data from other facilities. Finally, the paper outlines the underway research works at the mentioned facility and new directions for further work.

On the development of a deployable cold plasma endoscope

A novel non‐thermal atmospheric‐pressure plasma jet source for endoscopic application is presented. Specific challenges in the endoscopic plasma source development, such as small dimensions, flexibility, operation in half‐closed cavities, and the avoidance of in‐tube plasma, are addressed. Besides plasma characterization of the jet freely operating in ambient air, special focus is laid on the investigation of in‐cavity operation. In order to avoid saturation of the cavity atmosphere with the feed gas and at the same time allow a distinct jet formation, a second gas with electronegative properties is introduced as shielding gas. Depending on the flow rate ratios between feed gas and the shielding gas, arcing and jet‐to‐glow transition can be suppressed.

Jet Noise Shielding Provided by a Hybrid Wing Body Aircraft.

One approach toward achieving NASA's aggressive N+2 noise goal of 42 EPNdB cumulative margin below Stage 4 is through the use of novel vehicle configurations like the Hybrid Wing Body (HWB). Jet noise measurements from an HWB acoustic test in the NASA Langley 14- by 22-Foot Subsonic Tunnel are described. Two dual-stream, heated Compact Jet Engine Simulator (CJES) units are mounted underneath the inverted HWB model on a traversable support to permit measurement of varying levels of shielding provided by the fuselage. Both an axisymmetric and low noise chevron nozzle set are investigated in the context of shielding. The unshielded chevron nozzle set shows 1 to 2 dB of source noise reduction (relative to the unshielded axisymmetric nozzle set) with some penalties at higher frequencies. Shielding of the axisymmetric nozzles shows up to 6.5 dB of reduction at high frequency. The combination of shielding and low noise chevrons shows benefits beyond the expected additive benefits of the two, up to 10 dB, due to the effective migration of the jet source peak noise location upstream for increased shielding effectiveness. Jet noise source maps from phased array results processed with the Deconvolution Approach for the Mapping of Acoustic Sources (DAMAS) algorithm reinforce these observations.

How to constrain mass and spin of supermassive black holes through their disk emission

We investigate the global properties of the radiation emitted by the accretion disk around Kerr black holes. Using the Kerr blackbody numerical model, we build an analytic approximation of the disk emission features focusing on the pattern of the produced radiation as a function of the black hole spin, mass, accretion rate and viewing angle. The assumption of having a geometrically thin disk limits our analysis to systems emitting below ~0.3 of the Eddington luminosity. We apply this analytical model to four blazars (whose jets are pointing at us) at high redshift that show clear signatures of disk emission. For them, we derive the black hole masses as a function of spin. If these jetted sources are powered by the black hole rotation, they must have high spin values, further constraining their masses.

Supersonic plasma jets in experiments for radiophysical testing of bodies flow

The action of differently oriented magnetic fields on the parameters of bow shock created in the vicinity of aerodynamic bodies placed into the supersonic gas-plasma flows is studied. For these experiments two types of the high speed plasma jet sources are used—magneto-plasma compressor (MPC) and powerful pulse capillary type discharge. MPC allows to create the plasma jets with gas flow velocity of 10 ± 2 km/s, lifetime 30–50 μs, temperature Te ≈ 3 ± 0.5 eV, electron density about ne ∼ 1016cm−3 and temperature Te ≈ 3 ± 0.5 eV. The jet source based on powerful capillary discharge creates the flows with lifetime 1–20 ms, Mach numbers 3–8, plasma flow velocity 3–10 km/s, vibration and rotation temperatures 9000–14000 and 3800–6000 K respectively. The results of our first experiments show the possibility of using gas-plasma sources based on MPC and powerful capillary discharge for aerodynamic and radiophysical experiments. Comparatively small magnetic field B = 0.23–0.5 T, applied to the obtained bow shocks, essentially modify them. This can lead to a change in shape and an increase in the distance between the detached shock wave and the streamlined body surface if B is parallel to the jet velocity or to decrease this parameter if B is orthogonal to the oncoming flow. Probably, the first case can be useful for reducing the thermal load and aerodynamic drug of streamlined body and the second case can be used to control the radio-transparency of the plasma layer and solving the blackout problem.

Transonic region formation at the thermal and gas-dynamic action on a supersonic duct flow

The control simultaneous action of a jet and near-wall energy sources on the shockwave structure of a superso-nic flow in the axisymmetric and planar ducts is studied for the purpose of creating a transonic region. The regimes with an extended transonic region are obtained.

Confocal micro-X-ray fluorescence spectroscopy with a liquid metal jet source

To further widen the applicability of confocal micro-X-ray fluorescence spectroscopy (CMXRF) a novel setup using a liquid metal jet source as excitation was build up and characterized.

Spiky Structures around Reconnection Exhausts in the Solar Wind

Abstract The paper presents for the first time observations of unusual reconnection events in the solar wind. In all solar wind types, we identify magnetic reconnection exhausts accompanied by one or two side jets. This complex structure is created around a single current sheet and the jet(s) oriented in the same direction as the main exhaust is (are) spatially separated from it. A statistical analysis of reconnection exhausts in Wind observations (422 events) revealed that about 12% of exhausts is accompanied with one side jet and 3% of exhausts is bounded by two side jets, one on each side. Multispacecraft observations of events allow us to conclude that these structures are not consistent with a folding of the reconnection exhaust boundary. A source of these side jets is probably multiple or patchy reconnection at or close to the heliospheric current sheet. We suggest a scenario based on multiple reconnection that would lead to the presence of two side jets. A single jet is caused by a broken X-line consisting of two or more spatially separated parts.

A Jet Source of Event Horizon Telescope Correlated Flux in M87

Abstract Event Horizon Telescope (EHT) observations at 230 GHz are combined with Very Long Baseline Interferometry (VLBI) observations at 86 GHz and high-resolution Hubble Space Telescope optical observations in order to constrain the broadband spectrum of the emission from the base of the jet in M87. The recent VLBI observations of Hada et al. provide much stricter limits on the 86 GHz luminosity and component acceleration in the jet base than were available to previous modelers. They reveal an almost hollow jet on sub-mas scales. Thus, tubular models of the jet base emanating from the innermost accretion disk are considered within the region responsible for the EHT correlated flux. There is substantial synchrotron self-absorbed opacity at 86 GHz. A parametric analysis indicates that the jet dimensions and power depend strongly on the 86 GHz flux density and the black hole spin, but depend weakly on other parameters, such as jet speed, 230 GHz flux density, and optical flux. The entire power budget of the M87 jet, , can be accommodated by the tubular jet. No invisible, powerful spine is required. Even though this analysis never employs the resolution of the EHT, the spectral shape implies a dimension transverse to the jet direction of 12–21 ( ) for ( ), where M is the mass and a is the angular momentum per unit mass of the central black hole.

RAiSE III: 3C radio AGN energetics and composition

Kinetic jet power estimates based exclusively on observed monochromatic radio luminosities are highly uncertain due to confounding variables and a lack of knowledge about some aspects of the physics of active galactic nuclei (AGNs). We propose a new methodology to calculate the jet powers of the largest, most powerful radio sources based on combinations of their size, lobe luminosity and shape of their radio spectrum; this approach avoids the uncertainties encountered by previous relationships. The outputs of our model are calibrated using hydrodynamical simulations and tested against independent X-ray inverse-Compton measurements. The jet powers and lobe magnetic field strengths of radio sources are found to be recovered using solely the lobe luminosity and spectral curvature, enabling the intrinsic properties of unresolved high-redshift sources to be inferred. By contrast, the radio source ages cannot be estimated without knowledge of the lobe volumes. The monochromatic lobe luminosity alone is incapable of accurately estimating the jet power or source age without knowledge of the lobe magnetic field strength and size respectively. We find that, on average, the lobes of the 3C radio sources have magnetic field strengths approximately a factor three lower than the equipartition value, inconsistent with equal energy in the particles and the fields at the 5$\sigma$ level. The particle content of 3C radio lobes is discussed in the context of complementary observations; we do not find evidence favouring an energetically-dominant proton population.

Fermi Non-detections of Four X-Ray Jet Sources and Implications for the IC/CMB Mechanism

Abstract Since its launch in 1999, the Chandra X-ray observatory has discovered several dozen X-ray jets associated with powerful quasars. In many cases, the X-ray spectrum is hard and appears to come from a second spectral component. The most popular explanation for the kpc-scale X-ray emission in these cases has been inverse-Compton (IC) scattering of Cosmic Microwave Background (CMB) photons by relativistic electrons in the jet (the IC/CMB model). Requiring the IC/CMB emission to reproduce the observed X-ray flux density inevitably predicts a high level of gamma-ray emission, which should be detectable with the Fermi Large Area Telescope (LAT). In previous work, we found that gamma-ray upper limits from the large-scale jets of 3C 273 and PKS 0637−752 violate the predictions of the IC/CMB model. Here, we present Fermi/LAT flux density upper limits for the X-ray jets of four additional sources: PKS 1136–135, PKS 1229–021, PKS 1354+195, and PKS 2209+080. We show that these limits violate the IC/CMB predictions at a very high significance level. We also present new Hubble Space Telescope observations of the quasar PKS 2209+080 showing a newly detected optical jet, and Atacama Large Millimeter/submillimeter Array band 3 and 6 observations of all four sources, which provide key constraints on the spectral shape that enable us to rule out the IC/CMB model.

Very Large Array Ammonia Observations of the HH 111/HH 121 Protostellar System: A Detection of a New Source with a Peculiar Chemistry

Abstract We present the results of Very Large Array NH3 ( J , K ) = ( 1 , 1 ) and ( 2 , 2 ) observations of the HH 111/HH 121 protostellar system. HH 111, with a spectacular collimated optical jet, is one of the most well-known Herbig–Haro objects. We report the detection of a new source, NH3–S, in the vicinity of HH 111/HH 121 (∼0.03 pc from the HH 111 jet source) in two epochs of the ammonia observations. This constitutes the first detection of this source, in a region that has been thoroughly covered previously by both continuum and spectral line interferometric observations. We study the kinematic and physical properties of HH 111 and the newly discovered NH3–S. We also use HCO+ and HCN ( J = 4 − 3 ) data obtained with the James Clerk Maxwell Telescope and archival Atacama Large Millimeter/submillimeter Array 13CO, 12CO, and C18O ( J = 2 − 1 ) , N2D+ ( J = 3 − 2 ) , and 13CS ( J = 5 − 4 ) data to gain insight into the nature of NH3–S. The chemical structure of NH3–S shows evidence for “selective freeze-out,” an inherent characteristic of dense cold cores. The inner part of NH3–S shows subsonic nonthermal velocity dispersions indicating a “coherent core,” while they increase in the direction of the jets. Archival near- to far-infrared data show no indication of any embedded source in NH3–S. The properties of NH3–S and its location in the infrared dark cloud suggest that it is a starless core located in a turbulent medium, with the turbulence induced by Herbig–Haro jets and associated outflows. More data are needed to fully understand the physical and chemical properties of NH3–S and if/how its evolution is affected by nearby jets.

Aerodynamic acceleration of heavy particles in a supersonic jet of a binary mixture of gases with disparate-mass components

The method of moments for the ellipsoidal distribution function was used for solving the Boltzmann equation describing binary gas mixtures with large mass disparity and highly diluted heavy component. Analysis of the system of moment equations results in a simple analytic expression for the terminal slip velocities of components that depends on the conditions in the source of jet, composition of mixture, and C6 constant of the attractive branch of the interaction potential. The results are in good agreement with experimental data including low pressure conditions when the Miller-Andres correlation is unsatisfactory.

The effect of localized pulse-periodic energy supply on supersonic mixing in channels

Results of numerical simulations of supersonic flows in flat channels with narrowing and expanding input sections confirm the possibility of intensification of the mixing of a low-density supersonic gas jet with surrounding co-current flow by means of a localized pulse-periodic energy supply. The influence of the positions of the jet and energy-supply source on the formation of large-scale vortex structures favoring the intensification of mixing is demonstrated.

CALYPSO view of SVS 13A with PdBI: Multiple jet sources

Aims. We aim to clarify the origin of the multiple jet features emanating from the binary protostar SVS 13A (=VLA4A/VLA4B). Methods. We used the Plateau de Bure Interferometer to map at 0.3–0.8′′ (~70–190 au) dust emission at 1.4 mm, CO(2–1), SiO(5–4), SO(65–54). Revised proper motions for VLA4A/4B and jet wiggling models are computed to clarify their respective contribution. Results. VLA4A shows compact dust emission suggestive of a disk <50 au, and is the hot corino source, while CO/SiO/SO counterparts to the small-scale H2 jet originate from VLA4B and reveal the jet variable velocity structure. This jet exhibits ≃ 3″ wiggling consistent with orbital motion around a yet undetected ≃20–30 au companion to VLA4B, or jet precession. Jet wiggling combined with velocity variability can explain the large apparent angular momentum in CO bullets. We also uncover a synchronicity between CO jet bullets and knots in the HH7–11 chain demonstrating that they trace two distinct jets. Their ≃300 yr twin outburst period may be triggered by close perihelion approach of VLA4A in an eccentric orbit around VLA4B. A third jet is tentatively seen at PA ≃ 0°. Conclusions. SVS13 A harbors at least 2 and possibly 3 distinct jet sources. The CO and HH7-11 jets are launched from quasi-coplanar disks, separated by 20–70 au. Their synchronous major events every 300 yr favor external triggering by close binary interactions, a scenario also invoked for FU Or outbursts.