Methodologies for inclusion of fluid stress, added mass, and Basset history forces when modeling particle motion in a high-pressure gas jet

We demonstrate a compact extreme ultraviolet (XUV) source based on high-harmonic generation (HHG) driven directly inside the cavity of a mode-locked thin-disk laser oscillator. The laser is directly diode-pumped at a power of only 51 W and operates at a wavelength of 1034 nm and a 17.35 MHz repetition rate. We drive HHG in a high-pressure xenon gas jet with an intracavity peak intensity of 2.8×1013 W/cm2 and 320 W of intracavity average power. Despite the high-pressure gas jet, the laser operates at high stability. We detect harmonics up to the 17th order (60.8 nm, 20.4 eV) and estimate a flux of 2.6×108 photons/s for the 11th harmonic (94 nm, 13.2 eV). Due to the power scalability of the thin-disk concept, this class of compact XUV sources has the potential to become a versatile tool for areas such as attosecond science, XUV spectroscopy, and high-resolution imaging.

A visual experiment platform for high-pressure gas jet impacting the bulk-loaded liquid was designed and built in order to investigate the real law of the interaction between the high-pressure gas jet and the liquid medium during the liquid-balance launch of rocket launcher. The experiments of single-phase gas jet injection and the high-pressure gas jet at different temperatures impacting the bulk-loaded liquid were carried out, and the effects of gas temperature on the characteristics of the gas-liquid flow field have been revealed. The results show that the turbulent mixing between the high-pressure gas jet and the liquid medium leads to the appearance of pressure fluctuations in the gas chamber connected to the nozzle. The higher the gas temperature, the greater the amplitude of the pressure fluctuations. Under the impact of high-pressure gas jet, a gas cavity with an arc-shaped head is formed inside the bulk-loaded liquid. The higher the gas temperature, the faster and more unstable the development of the gas cavity and the flow field. The displacement equation of the gas cavity confirms to the first-order exponential decay function, and the error between the fitting value of the established mathematical model and the measured value is within 2%.

In view of the defects of borehole collapse, inhibition of gas desorption and migration of gas existing in hydraulic fracturing and other hydraulic permeability–increasing measures for soft coal seams with low-permeability technology is proposed for coal breakage by a high-pressure abrasive gas jet for relieving pressure and increasing permeability. The comparative analysis of gas jet flow field structure between convergent nozzle and Laval nozzle has been given by numerical simulation. For Laval nozzle, the expansion wave and compression wave alternate and move forward steadily in gas jet and vanish when potential core length reaches maximum. So, the Laval nozzle can form more stable flow filed structure of gas jet and avoid shock wave in gas jet. Furthermore, a high-speed camera is adopted to analyze the jet structure and verify the conclusion of numerical simulation. Based on thermodynamic theory, this article calculates and analyzes the critical local sound velocity and pressure generated from the stress wave during the process of coal breakage by the gas jet. Furthermore, experimental coal breakage by a high-pressure abrasive gas jet is carried out. The high-pressure abrasive gas jet impacts the coal body as a quasi-static load and a dynamic load and forms corrosion pits on the surface of the coal body. Penetrating cracks are formed within the coal in the pattern of the loaded stress wave which leads to coal breakage. The effects of porosity and permeability on the propagation of the stress wave in coal are analyzed by establishing the dispersion equation for the spread of the stress wave in coal. The results show that porosity has a significant effect on wave velocity and that the attenuation of the stress wave is intensified with an increase in porosity. Moreover, the stress wave attenuation is more obvious at high frequency. The effect of permeability on the wave velocity is not significant at low frequencies. In contrast, at high frequency and relatively low permeability, the wave velocity increases with the permeability, and the attenuation of the wave velocity initially increases and then decreases. When the permeability is greater than 10−11 m2, the wave velocity is not affected by the permeability. However, the stress wave is not attenuated.

Damaging effects of disruptions are a major concern for Alcator C-Mod, ITER and future tokamak reactors. High-pressure noble gas jet injection is a mitigation technique which potentially satisfies the operational requirements of fast response time and reliability, while still being benign to subsequent discharges. Disruption mitigation experiments using an optimized gas jet injection system are being carried out on Alcator C-Mod to study the physics of gas jet penetration into high pressure plasmas, as well as the ability of the gas jet impurities to convert plasma energy into radiation on timescales consistent with C-Mod's fast quench times, and to reduce halo currents given C-Mod's high-current density. The dependence of impurity penetration and effectiveness on noble gas species (He, Ne, Ar, Kr) is also being studied. It is found that the high-pressure neutral gas jet does not penetrate deeply into the C-Mod plasma, and yet prompt core thermal quenches are observed on all gas jet shots. 3D MHD modelling of the disruption physics with NIMROD shows that edge cooling of the plasma triggers fast growing tearing modes which rapidly produce a stochastic region in the core of the plasma and loss of thermal energy. This may explain the apparent effectiveness of the gas jet in C-Mod despite its limited penetration. The higher-Z gases (Ne, Ar, Kr) also proved effective at reducing halo currents and decreasing thermal deposition to the divertor surfaces. In addition, noble gas jet injection proved to be benign for plasma operation with C-Mod's metal (Mo) wall, actually improving the reliability of the startup in the following discharge.

Soft X-ray spectra have been obtained from laser-produced carbon, nitrogen, neon, and argon plasmas in the range between 50 and 500 eV. The plasmas were made by irradiating a high-pressure supersonic gas jet with 22-J, 3-ns pulses of 1.054- mu m laser light. This work is motivated by the recent success of recombination-pumped hydrogenlike carbon lasers at 182 AA (e.g., Suckewer et al., Phys. Rev. Lett., vol.55, p.1753, 1985). If sufficient laser energy can be coupled into the gas jet plasma, other low-Z elements such as nitrogen, oxygen, fluorine, and possibly neon could be stripped to the appropriate charge state and, presumably, laser. Because the laser energy needed to strip an atom depends sensitively on Z, these lower-Z ions are more accessible than higher-Z solid laser targets. In addition, X-ray lasing in lithiumlike ions could also be studied and would require even less laser energy. This low-Z sequence would supply a well defined set of X-ray lines which could be used for other scientific purposes. The spectra obtained show that hydrogenlike carbon and nitrogen are present in substantial abundance and that lithiumlike neon can be produced with the irradiation conditions used. >

The flow field of the underwater gas jet with high temperature and high pressure is a compressible multiphase flow with strong shock waves and large deformation. In this study, establishing a two-dimensional axisymmetric five-equation multiphase flow model, and using the Tangent of Hyperbola for Interface Capturing (THINC) method. The numerical simulation of the flow field of methane-oxygen underwater detonation with different filling pressure is carried out. By building a high-speed photography system and an underwater high-pressure gas jet experimental platform, the underwater gas jet by methane oxygen detonating with different filling pressure is studied. The experimental results show that the water possessing the features of hard compressibility and huge mass inertia makes the high-pressure gas jet bubble expand rapidly to both sides of the tube at the initial stage of formation, but expand rapidly obviously in the axial direction at the end of the first expansion circulating. With the increase of filling pressure, the radial expansion of the gas jet bubble is bigger and bigger, and the rewinding distance is increasing concomitantly. The experimental results also show that the first pulsating pressure increases gradually with the increase of packing pressure.

Visualization research on injection characteristics of high-pressure gas jets for natural gas engine

To investigate the interaction between a jet gas flow and combustion, we developed a three-dimensional numerical model. The flow characteristics [vorticity and turbulence kinetic energy (TKE)] were used to study the effect of the methane jet, while the combustion parameters [hydroxide radical (OH) mass fraction and heat release rate (HRR)] were used to study the effect of combustion. The results showed that the development of the methane jet flame was divided into three stages. In stage I, the methane jet interacted with the premixed flame; in stages II and III, both the flow characteristics and combustion parameters increased. This jet flame was induced by both the methane jet and the combustion. The jet flame velocity increased based on the interaction between the flow characteristics (represent by <i>K</i><sub>v</sub> and <i>K</i><sub>TKE</sub>) and combustion parameters (represent by <i>K</i><sub>OH</sub> and <i>K</i><sub>HRR</sub>). A dimensionless parameter (<i>K</i><sub>0</sub>) was adopted to represent the comparison between the flow characteristics and combustion, i.e., <i>K</i><sub>0</sub> = (<i>K</i><sub>OH</sub><i>K</i><sub>HRR</sub>)/(<i>K</i><sub>v</sub><i>K</i><sub>TKE</sub>). During stage I, <i>K</i><sub>0</sub> < 1 and the high-pressure methane jet played a major role. During stage II, initially, <i>K</i><sub>0</sub> > 1 and combustion played a slightly larger role than that of the high-pressure methane jet; later in stage II, <i>K</i><sub>0</sub> < 1, the high-pressure methane jet played a major role. During stage III, <i>K</i><sub>0</sub> > 1; this result revealed that the combustion played a dominant role while the high-pressure gas jet caused less effects late in stage III of the flame propagation process.

Ambient Tracer-LIF for 2-D quantitative measurement of fuel concentration in gas jets

This article presents the results of computational studies investigating the ignition of high-pressure natural gas jets in a compression-ignition engine with glow plug ignition assist. The simulation was conducted using a KIVA-3V-based three-dimensional engine model, along with an improved fuel injector model, a detailed cut-off glow plug shield model and a modified two-step methane reaction mechanism, to simulate the natural gas injection and ignition. The simulated results demonstrate the significance of using a shield for the glow plug. Compared to an unshielded (bare) glow plug, the shield not only reduces the heat loss from the hot glow plug surface to the cold intake air charge and the cold injected gas jet but also traps the fuel mixture to increase its residence time adjacent to the hot surface. Over a representative range of heavy-duty diesel engine operating conditions, a shielded glow plug greatly improves the natural gas engine performance and provides reliable ignition, while an unshielded glow plug can only be optimized for specific conditions. The understanding of glow plug shield behavior gained from the simulations suggests avenues for improved shield designs that would yield further reduced ignition delays.

An experimental system, which was composed of a high-pressure gas jet generator, transparent chambers with various interior geometries and a high-speed video recorder, was built for the investigation of interactions between high-pressure gas jet and bulk-loaded liquid. A gas-liquid two-phase turbulent flow model was also developed. The experimental and calculated results indicated that in the multi-stage stepped-wall combustion chamber, the two-phase flow was induced by the step, the radial expansion was enhanced and the axial expansion was retarded, thus the Taylor-Helmholtz instability which generated due to the effect of shear at gas-liquid interface decreased. The chamber geometry and the jet intensity had evident effects on the jet expanding and turbulent mixing processes. The presented work is helpful to better understand the physical processes of combustion gas expanding in bulk-loaded liquid.

While the transportation field is mostly characterized by the use of liquid fuels, gaseous fuels like hydrogen and natural gas have shown high thermal efficiency and low exhaust emissions when used in internal combustion engines (ICEs). In particular, high-pressure direct injection of a gaseous fuel within the cylinder overcomes the loss of volumetric efficiency and allows stratifying the mixture around the spark plug at the ignition time. Direct injection and mixture stratification can extend the lean flammability limit and improve efficiency and emissions of ICEs. Compared to liquid sprays, the phenomena involved in the evolution of gaseous jets are less complex to understand and model. Nevertheless, the numerical simulation of a high-pressure gas jet is not a simple task. At high injection pressure, immediately downstream of the nozzle exit the flow is supersonic, the gas is under-expanded, and a large series of shocks occurs due to the effect of compressibility. To simulate and capture these phenomena, grid resolution, computational time-step, discretization scheme, and turbulence model need to be properly set. The research group on hydrogen ICEs at Argonne National Laboratory has been extensively working on validating numerical results on gaseous direct injection and mixture formation against PIV and PLIF data from an optically accessible engine. While a good general agreement was observed, simulations still could not perfectly predict the mixing of fuel with the surrounding air, which sometimes led to significant under-prediction of fuel dispersion. The challenge is to correctly describe the gas dynamic phenomena of under-expanded gas jets. To this aim, x-ray radiography was performed at the Advanced Photon Source (APS) at Argonne to provide high-detail data of the mass distribution within a high-pressure gas jet, with the main focus on the under-expanded region. In this paper, the numerical simulation of high-pressure (100 bar) injection of argon in a cylindrical chamber is performed using the computational fluid dynamic (CFD) solver Fluent. Numerical results of jet penetration and mass distribution are compared with x-ray data. The simplest nozzle geometry, consisting of one hole with a diameter of 1 mm directed along the injector axis, is chosen as a canonical case for modeling validation. A sector (90°) mesh, with high resolution in the under-expanded region, is used and the assumption of symmetry is made. Results show good agreement between CFD and x-ray data. Gas dynamics and mass distribution within the jet are well predicted by numerical simulations.

This work investigated the effect of high-pressure (10 MPa) methane gas jet impinging on the methane lean-burn premixed flame (equivalent ratio of 0.7) based on a three-dimensional numerical simulation by CONVERGE software. The results show that laminar premixed flame is accelerated to develop into a stable turbulent flame under the action of the methane jet, the whole process of flame front development is divided into three stages: laminar (Reynolds number maintains stable, 1–1.3 ms), transition (Reynolds number shows an increasing trend, 1.4–8 ms), and turbulent (Reynolds number tends to stabilize at a high value, 1.9–3 ms). The effect of high-pressure jet on flame development along jet direction (Z axis) is greater than that on vertical direction (Y axis). During turbulence stage, the momentum and kinetic energy of Z axis are 2.7 and 6.3 times greater than that of Y axis, respectively. The high-pressure methane jet causes a change in heat distribution, resulting in local flameout. The rate of change in the local flameout area is greater than that in the flame area, causing a temperature drop in Z axis. This temperature drop increases with the increase in equivalence ratio and with the decrease in distance between cross-section position and ignition center.

We propose an optical method based on Rayleigh scattering for the direct measurement of cluster tracks produced by a high-pressure gas jet. The tracks of the argon and methane clusters are acquired by a high-speed camera. It is found that the cluster sizes of these tracks are within the range of 7E + 03~1E + 07 for argon and 2E + 06~4E + 08 for methane. Most argon tracks are continuous and their intensity changes gradually, while the majority of the methane tracks are separated into discrete fractions and their intensity alters periodically along the flight path, which may indicate the methane clusters are more unstable and easily to break up. Special methane clusters which may fly at an axial velocity of less than 2.5m/s are also found. This method is very sensitive to large gas cluster and has broad application prospects in cluster physics.

We present an all-optical method for measurement of the average size and density of clusters produced in high-pressure gas jets as targets for intense laser irradiation. The technique employs Rayleigh scattering imaging combined with interferometry.