Jet Source Research Articles

Experimental and computational study of a high-Reynolds jet flow

Three-dimensional jet flows at high Reynolds (Re) numbers, namely over a million, have a significant importance in hydraulic engineering. Despite their importance, most of the previous investigations have been mainly focused only on jet flows with orders of magnitude lower Re numbers. We present the results of an experimental campaign and a high fidelity large-eddy simulation (LES) to study a jet flow with Re ≈ 1.71 × 106 in a large-scale flume. Flow measurements are carried out using a pitot tube apparatus and the Virtual Flow Simulator (VFS-Geophysics) model is employed to simulate the flow field. The measured velocity field of the jet is used to evaluate the LES results. The presented experimental data for the cross-sectional velocity distributions at various distances from the jet source provide an unprecedented dataset for model validation at high Re numbers.

The assessment of cold atmospheric plasma treatment of DNA in synthetic models of tissue fluid, tissue and cells

There is a growing literature database that demonstrates the therapeutic potential of cold atmospheric plasma (herein referred to as plasma). Given the breadth of proposed applications (e.g. from teeth whitening to cancer therapy) and vast gamut of plasma devices being researched, it is timely to consider plasma interactions with specific components of the cell in more detail. Plasma can produce highly reactive oxygen and nitrogen species (RONS) such as the hydroxyl radical (OH•), peroxynitrite (ONOO−) and superoxide () that would readily modify essential biomolecules such as DNA. These modifications could in principle drive a wide range of biological processes. Against this possibility, the reported therapeutic action of plasmas are not underpinned by a particularly deep knowledge of the potential plasma-tissue, -cell or -biomolecule interactions.In this study, we aim to partly address this issue by developing simple models to study plasma interactions with DNA, in the form of DNA-strand breaks. This is carried out using synthetic models of tissue fluid, tissue and cells. We argue that this approach makes experimentation simpler, more cost-effective and faster than compared to working with real biological materials and cells. Herein, a helium plasma jet source was utilised for these experiments. We show that the plasma jet readily induced DNA-strand breaks in the tissue fluid model and in the cell model, surprisingly without any significant poration or rupture of the phospholipid membrane. In the plasma jet treatment of the tissue model, DNA-strand breaks were detected in the tissue mass after pro-longed treatment (on the time-scale of minutes) with no DNA-strand breaks being detected in the tissue fluid model underneath the tissue model. These data are discussed in the context of the therapeutic potential of plasma.

SPHERE/ZIMPOL observations of the symbiotic system R Aquarii

R Aqr is a symbiotic binary system consisting of a mira variable, a hot companion with a spectacular jet outflow, and an extended emission line nebula. We have used R Aqr as test target for the visual camera subsystem ZIMPOL, which is part of the new extreme adaptive optics (AO) instrument SPHERE at the Very Large Telescope (VLT). We compare our observations with data from the Hubble Space Telescope (HST) and illustrate the complementarity of the two instruments. We determine from the Halpha emission the position, size, geometric structure, and line fluxes of the jet source and the clouds in the innermost region (<2") of R Aqr and determine Halpha emissivities mean density, mass, recombination time scale, and other cloud parameters. Our data resolve for the first time the R Aqr binary and we measure for the jet source a relative position 46+/-1 mas West of the mira. The central jet source is the strongest Halpha component. North east and south west from the central source there are many clouds with very diverse structures. We see in the SW a string of bright clouds arranged in a zig-zag pattern and, further out, more extended bubbles. In the N and NE we see a bright, very elongated filamentary structure and faint perpendicular "wisps" further out. Some jet clouds are also detected in the ZIMPOL [OI] and He I filters, as well as in the HST line filters for Halpha, [OIII], [NII], and [OI]. We determine jet cloud parameters and find a very well defined anti-correlation between cloud density and distance to the central binary. Future Halpha observations will provide the orientation of the orbital plane of the binary and allow detailed hydrodynamical investigations of this jet outflow and its interaction with the wind of the red giant companion.

Probing stochastic inter-galactic magnetic fields using blazar-induced gamma ray halo morphology

Inter-galactic magnetic fields can imprint their structure on the morphology of blazar-induced gamma ray halos. We show that the halo morphology arises through the interplay of the source's jet and a two-dimensional surface dictated by the magnetic field. Through extensive numerical simulations, we generate mock halos created by stochastic magnetic fields with and without helicity, and study the dependence of the halo features on the properties of the magnetic field. We propose a sharper version of the Q-statistics and demonstrate its sensitivity to the magnetic field strength, the coherence scale, and the handedness of the helicity. We also identify and explain a new feature of the Q-statistics that can further enhance its power.

Dynamics of apokamp-type atmospheric pressure plasma jets initiated in air by a repetitive pulsed discharge

This paper presents the research data on the dynamics of a repetitive pulsed discharge as a source of plasma jets in atmospheric pressure air and on the conditions under which the discharge produces apokamp–plasma jets ejected from the bending point of the discharge channel with no gas supply through the discharge region. The data suggest that the formation of apokamps requires the application of a large number of voltage pulses to sharp-ended electrodes at a repetition frequency of several to tens of kilohertz. Before an apokamp starts developing, the apokamp-initiating discharge passes through a spark stage and then becomes diffuse. Next, at the site of electric field amplification, the discharge channel gives rise to a bright branch from which plasma bullets escape with a velocity of ∼200 km/s. The images of different discharge and apokamp stages are presented.

Application of Metabolomics and Fluxomics to Study Fatty Acid Synthesis in Alternative Crops

The goal of this research is to address the need for an alternative supply of jet fuel using native plants that do not compete with food crops. Pennycress (Thlaspi arvense), a member of the Brassicaceae, has been identified as a promising bioenergy crop: the chemical composition of its oil is ideally suited as a renewable source of biodiesel and jet fuel. This plant has tremendous potential for large‐scale oil production, has a short maturity time and is not a food crop. Pennycress can be commercially propagated as a winter annual, and has therefore the potential to be grown off‐season, complementing, rather than competing, the production of commodity crops, and serving as a winter cover crop. However, for this plant to become an economically viable source of specialty fuels, molecular and genetic resources need to be developed to facilitate and enhance oil production by breeding and/or genetic manipulation. This study aims to find potential biochemical step(s) that limit(s) oil synthesis, which will serve as targets for future crop improvement.To advance towards this goal, we determined the intracellular metabolite levels (metabolomics) in pennycress embryos at different stages of development. For this purpose, we have developed novel and highly sensitive methodologies using state‐of‐the‐art liquid chromatography tandem mass spectrometry (LC‐MS/MS). This metabolomics study highlighted the metabolites and pathways that were active in pennycress embryos and important for oil production. The contribution of each pathway to fatty acid synthesis in terms of carbon, reductant and energy provision is being assessed by measuring the carbon flow through the metabolic network. We are hence performing a 13C‐Metabolic Flux Analysis (fluxomics) in developing pennycress embryos to build a map of carbon flow through central metabolism. This study describes the combination of innovative tools that will pave the way for controlling seed composition in promising alternative crops.Support or Funding InformationJ.C.C was supported in part by the Agriculture and Food Research Initiative competitive grant # 2016‐67013‐24605 of the USDA National Institute of Food and Agriculture. This study is supported by the USDA‐U.S. Department of Energy Plant Feedstocks in Genomics for Bioenergy under Award Number DE‐SC0016490.

A decadal satellite record of gravity wave activity in the lower stratosphere to study polar stratospheric cloud formation

Abstract. Atmospheric gravity waves yield substantial small-scale temperature fluctuations that can trigger the formation of polar stratospheric clouds (PSCs). This paper introduces a new satellite record of gravity wave activity in the polar lower stratosphere to investigate this process. The record is comprised of observations of the Atmospheric Infrared Sounder (AIRS) aboard NASA's Aqua satellite from January 2003 to December 2012. Gravity wave activity is measured in terms of detrended and noise-corrected 15 µm brightness temperature variances, which are calculated from AIRS channels that are the most sensitive to temperature fluctuations at about 17–32 km of altitude. The analysis of temporal patterns in the data set revealed a strong seasonal cycle in wave activity with wintertime maxima at mid- and high latitudes. The analysis of spatial patterns indicated that orography as well as jet and storm sources are the main causes of the observed waves. Wave activity is closely correlated with 30 hPa zonal winds, which is attributed to the AIRS observational filter. We used the new data set to evaluate explicitly resolved temperature fluctuations due to gravity waves in the European Centre for Medium-Range Weather Forecasts (ECMWF) operational analysis. It was found that the analysis reproduces orographic and non-orographic wave patterns in the right places, but that wave amplitudes are typically underestimated by a factor of 2–3. Furthermore, in a first survey of joint AIRS and Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) satellite observations, nearly 50 gravity-wave-induced PSC formation events were identified. The survey shows that the new AIRS data set can help to better identify such events and more generally highlights the importance of the process for polar ozone chemistry.

From free jets to clinging wall jets: The influence of a horizontal boundary on a horizontally forced buoyant jet

Laboratory experiments examine the interaction of a horizontal round buoyant jet with a horizontal surface near the jet source.

Dynamics of apokamp-type atmospheric pressure plasma jets

The paper describes a new discharge source of atmospheric pressure plasma jets (APPJs) in air with no gas supply through the discharge region. In this discharge mode, plasma jets develop from the bending point of a bright current channel between two electrodes and are therefore termed an apokamp (from Greek ‘off’ and ‘bend’). The apokamp can represent single plasma jets of length up 6 cm or several jets, and the temperature of such jets can range from more than 1000 °C at their base to 100–250 °C at their tip. Apokamps are formed at maximum applied voltage of positive polarity, provided that the second electrode is capacitively decoupled with ground. According to high-speed photography with time resolution from several nanoseconds to several tens of nanoseconds, the apokamp consists of a set of plasma bullets moving with a velocity of 100–220 km/s, which excludes the convective mechanism of plasma decay. Estimates on a 100-ns scale show that the near-electrode zones and the zones from which apokamps develop are close in temperature.

Relativistic Jets in Active Galactic Nuclei and Microquasars

Collimated outflows (jets) appear to be a ubiquitous phenomenon associated with the accretion of material onto a compact object. Despite this ubiquity, many fundamental physics aspects of jets are still poorly understood and constrained. These include the mechanism of launching and accelerating jets, the connection between these processes and the nature of the accretion flow, and the role of magnetic fields; the physics responsible for the collimation of jets over tens of thousands to even millions of gravitational radii of the central accreting object; the matter content of jets; the location of the region(s) accelerating particles to TeV (possibly even PeV and EeV) energies (as evidenced by gamma-ray emission observed from many jet sources) and the physical processes responsible for this particle acceleration; the radiative processes giving rise to the observed multi-wavelength emission; and the topology of magnetic fields and their role in the jet collimation and particle acceleration processes. This chapter reviews the main knowns and unknowns in our current understanding of relativistic jets, in the context of the main model ingredients for Galactic and extragalactic jet sources. It discusses aspects specific to active Galactic nuclei (especially blazars) and microquasars, and then presents a comparative discussion of similarities and differences between them.

A review of dispersion modelling of agricultural emissions with non-point sources

This paper presents a review of pollutant dispersion modelling from non-point sources, focused on agricultural and bioaerosol sources. Relevant non-point source characteristics were collated from a literature review. These values were used to describe a 'typical' agricultural source using line, area, volume and jet source types in the plume dispersion models ADMS and AERMOD; predicted downwind pollutant concentrations are compared. The modelling shows that predicted ground-level concentrations beyond approximately 100 m downwind are similar for the majority of non-point source types. ADMS and AERMOD were used to represent releases from four sheds housing intensively farmed poultry as a case study. When the emission and volume flow rates used in the modelling were derived from measurements, the models give reasonably accurate predictions. However for releases with non-negligible efflux, modelling using non-point sources allowing for the momentum and buoyancy of the release has much better agreement with observations than those that do not.

Coherent structures and wavepackets in subsonic transitional turbulent jets

A large eddy simulation (LES) is performed for two subsonic jets with a Reynolds number of \(Re=10^5\), which have different core temperatures, i.e., the cold and hot jet. The far-field overall sound pressure levels (OASPL) and noise spectra are well validated against previous experimental results. It is found that the OASPL is raised by heating at shallow angles. The most energetic coherent structures are extracted with specified frequencies using the filter based on the frequency domain variant of the snapshot method of proper orthogonal decomposition (POD). The \(m=0,1\) modes have high coherence of near-field pressure for both jets, while the coherence of \(m=0\) modes is enhanced greatly by heating. Based on the coherent structures, spatial wavepackets are educed and the characteristics of growth, saturation and decay are analyzed and compared between the two jets in detail. The results show that heating would enhance the linear growth rate for high frequency components, and nonlinear growth rates for low frequency components in general, which are responsible for higher OASPL in the hot jet. The far-field sound generated by wavepackets is computed using the Kirchhoff extrapolation, which matches well with that of LES at shallow angles. This indicates that the wavepackets associated with coherent structures are dominant sound sources in forced transitional turbulent jets. Additionally, the present POD method is proven to be a robust tool to extract the salient features of the wavepackets in turbulent flows.

Atmospheric pressure non-equilibrium plasma cleaning of 19th century daguerreotypes

In the work, the feasibility of using atmospheric pressure non-equilibrium plasmas to clean the surface of a deteriorated 19th century daguerreotype has been examined and a proof-of-principle demonstration is given. The daguerreotype was treated by means of both a commercial plasma jet source (kINPen 09, Neoplas Tools GmbH) and a specially designed Dielectric Barrier Discharge (DBD) plasma source operated within a controlled volume at atmospheric pressure, by using a argon-hydrogen gas mixture (H2 content: 35% vol.) to remove corrosion products, without immersion of the substrate in solvents or chemicals. The effectiveness of plasma treatment in removing tarnishing products while preventing damage to the fragile image has been evaluated analysing the surface by means of scanning electron microscopy (SEM) with energy dispersive microprobe (EDS) for localized elemental analysis, micro-Raman and ATR-FTIR spectroscopy for phase identification.

Probing acceleration and turbulence at relativistic shocks in blazar jets

Diffusive shock acceleration (DSA) at relativistic shocks is widely thought to be an important acceleration mechanism in various astrophysical jet sources, including radio-loud active galactic nuclei such as blazars. Such acceleration can produce the non-thermal particles that emit the broadband continuum radiation that is detected from extragalactic jets. An important recent development for blazar science is the ability of Fermi-LAT spectroscopy to pin down the shape of the distribution of the underlying non-thermal particle population. This paper highlights how multi-wavelength spectra spanning optical to X-ray to gamma-ray bands can be used to probe diffusive acceleration in relativistic, oblique, magnetohydrodynamic (MHD) shocks in blazar jets. Diagnostics on the MHD turbulence near such shocks are obtained using thermal and non-thermal particle distributions resulting from detailed Monte Carlo simulations of DSA. These probes are afforded by the characteristic property that the synchrotron $\nu F_{\nu}$ peak energy does not appear in the gamma-ray band above 100 MeV. We investigate self-consistently the radiative synchrotron and inverse Compton signatures of the simulated particle distributions. Important constraints on the diffusive mean free paths of electrons, and the level of electromagnetic field turbulence are identified for three different case study blazars, Mrk 501, BL Lacertae and AO 0235+164. The X-ray excess of AO 0235+164 in a flare state can be modelled as the signature of bulk Compton scattering of external radiation fields, thereby tightly constraining the energy-dependence of the diffusion coefficient for electrons. The concomitant interpretations that turbulence levels decline with remoteness from jet shocks, and the probable significant role for non-gyroresonant diffusion, are posited.

Spectral and Polarization Signatures of Relativistic Shocks in Blazars

Relativistic shocks are one of the most plausible sites of the emission of strongly variable, polarized multi-wavelength emission from relativistic jet sources such as blazars, via the diffusive shock acceleration (DSA) of relativistic particles. This paper summarizes recent results on a self-consistent coupling of diffusive shock acceleration and radiation transfer in blazar jets. We demonstrate that the observed spectral energy distributions (SEDs) of blazars strongly constrain the nature of hydromagnetic turbulence responsible for pitch-angle scattering by requiring a strongly energy-dependent pitch-angle mean free path. The prominent soft X-ray excess (“Big Blue Bump”) in the SED of the BL Lac object AO 0235+164 can be modelled as the signature of bulk Compton scattering of external radiation fields by the thermal electron population, which places additional constraints on the level of hydromagnetic turbulence. It has further been demonstrated that internal shocks propagating in a jet pervaded by a helical magnetic field naturally produce polarization-angle swings by 180 ∘ , in tandem with multi-wavelength flaring activity, without requiring any helical motion paths or other asymmetric jet structures. The specific application of this model to 3C279 presents the first consistent simultaneous modeling of snap-shot SEDs, multi-wavelength light curves, and time-dependent polarization signatures of a blazar during a polarization-angle (PA) rotation. This model has recently been generalized to a lepto-hadronic model, in which the high-energy emission is dominated by proton synchrotron radiation. It is shown that in this case, the high-energy (X-ray and γ-ray) polarization signatures are expected to be significantly more stable (not showing PA rotations) than the low-energy (electron-synchrotron) signatures.

Correlation between helium atmospheric pressure plasma jet (APPJ) variables and plasma induced DNA damage

A helium atmospheric pressure plasma jet (APPJ) source with a dielectric capillary and two tubular electrodes was used to induce damage in aqueous plasmid DNA. The fraction of different types of DNA damage (i.e., intact or undamaged, double strand breaks (DSBs), and single strand breaks (SSBs)) that occurred as the result of plasma irradiation was quantified through analysis of agarose gel electrophoresis images. The total DNA damage increased with an increase in both flow rate and duration of irradiation, but decreased with an increase in distance between the APPJ and sample. The average power of the plasma was calculated and the length of APPJ was measured for various flow rates and voltages applied. The possible effects of plasma power and reactive species on DNA damage are discussed.

MOPTOP: Multi-colour Optimised Optical Polarimeter

AbstractPolarimetric measurements are essential for the study of jetted sources associated with black holes, such as γ-ray bursts and blazars. The relativistic jets launched from regions close to the black hole are threaded with magnetic fields, which produce synchrotron emission, and can be studied with polarimetric measurements. The multi-colour, optimised, optical polarimeter (MOPTOP) is a multi-band imaging instrument designed for use on the Liverpool Telescope. By replacing the rotating polaroid with a half wave plate and beam splitter, the instrument utilises twice as much of the incoming beam of light from the telescope compared to its predecessor, Ringo3. MOPTOP also builds on the successful introduction of dichroic mirrors to perform simultaneous multi-waveband polarimetric and photometric analysis in Ringo3, and enhances the sensitivity of the instrument with sCMOS cameras to use all photons as efficiently as possible.

Application of Tomo-PIV in a large-scale supersonic jet flow facility

Particle imaging velocimetry (PIV) has been used extensively at NASA GRC over the last 15 years to build a benchmark data set of hot and cold jet flow measurements in an effort to understand acoustic noise sources in high-speed jets. Identifying the noise sources in high-speed jets is critical for ultimately modifying the nozzle hardware design/operation and therefore reducing the jet noise. Tomographic PIV (Tomo-PIV) is an innovative approach for acquiring and extracting velocity information across extended volumes of a flow field, enabling the computation of additional fluid mechanical properties not typically available using traditional PIV techniques. The objective of this work was to develop and implement the Tomo-PIV measurement capability and apply it in a large-scale outdoor test facility, where seeding multiple flow streams and operating in the presence of daylight presents formidable challenges. The newly developed Tomo-PIV measurement capability was applied in both a subsonic M 0.9 flow and an under-expanded M 1.4 heated jet flow field. Measurements were also obtained using traditional two-component (2C) PIV and stereo PIV in the M 0.9 flow field for comparison and validation of the Tomo-PIV results. In the case of the M 1.4 flow, only the 2C PIV was applied to allow a comparison with the Tomo-PIV measurement. The Tomo-PIV fields-of-view covered 180 × 180 × 10 mm, and the reconstruction domains were 3500 × 3500 × 200 voxels. These Tomo-PIV measurements yielded all three components of vorticity across entire planes for the first time in heated supersonic jet flows and provided the first full 3D reconstruction of the Mach disk and oblique shock intersections inside of the barrel shocks. Measuring all three components of vorticity across multiple planes in the flow, potentially reduces the number of measurement configurations (streamwise and cross-stream PIV) required to fully characterize the mixing-enhanced nozzle flows routinely studied in aeroacoustics research.

Experimental study of propagation of instability waves in a submerged jet under transverse acoustic excitation

An experimental study was conducted on the specific features of instability wave propagation in the mixing layer of a turbulent jet when the jet is excited by an external acoustic wave. We used the technique of conditional phase averaging of data obtained by particle image velocimetry using the reference signal of a microphone placed near the jet. The influence of the excitation frequency on the characteristics of large-scale structures in the mixing layer was investigated. It is shown that the propagation patterns of the instability waves agree well with previously obtained data on the localization of acoustic sources in turbulent jets.

Comparative study of alternative biofuels on aircraft engine performance

Aviation industries are vulnerable to the energy crisis and simultaneously posed environmental concerns. Proposed engine technology advancements could reduce the environmental impact and energy consumption. Substituting the source of jet fuel from fossil-based fuel to biomass-based fuel will help reduce emissions and minimize the energy crisis. The present paper addresses the analysis of aircraft engine performance in terms of thrust, fuel flow and specific fuel consumption at different mixing ratio percentages (20%, 40%, 50%, 60% and 80%) of alternative biofuel blends already used in flight test (Algae biofuel, Camelina biofuel and Jatropha biofuel) at different flight conditions. In-house computer software codes, PYTHIA and TURBOMATCH, were used for the analysis and modeling of a three-shaft high-bypass-ratio engine which is similar to RB211-524. The engine model was verified and validated with open literature found in the test program of bio-synthetic paraffinic kerosene in commercial aircraft. The results indicated that lower heating value had a significant influence on thrust, fuel flow and specific fuel consumption at every flight condition and at all mixing ratio percentages. Wide lower heating value differences between two fuels give a large variation on the engine performances. Blended Kerosene–Jatropha biofuel and Kerosene–Camelina biofuel showed an improvement on gross thrust, net thrust, reduction of fuel flow and specific fuel consumption at every mixing ratio percentage and at different flight conditions. Moreover, the pure alternative of Jatropha biofuel and Camelina biofuel gave much better engine performances. This was not the case for the Kerosene–Algae blended biofuel. This study is a crucial step in understanding the influence of different blended alternative biofuels on the performance of aircraft engines.