Gas Dynamic Model Research Articles

Gas jet target with controllable density via throat diameter of conical nozzle

A supersonic gas jet has been a special target in the ultraintense laser interaction field due to its controllable atomic density distribution. This work investigates the spatial atomic density distribution in argon gas jets ejected from conical nozzles with different throat diameters. Both experiment and simulation results show that the atomic density and its distribution can be controlled by changing the throat diameter of the conical nozzle. The quantitative dependence of atomic density on the throat diameter under different backing pressures is obtained. It also agrees with that from the one-dimensional gas dynamics model. However, it is noted that for a large throat diameter at a high gas backing pressure, a radial saddle-shaped atomic density profile is demonstrated experimentally within a few millimeters away from the nozzle outlet. The results are helpful to optimize the density profile in gas-jet targets and to understand the effect of the throat diameter of the conical nozzle on cluster size in Hagena scaling law.

Modeling the influence of the duration of water vapor pulses on the properties of hafnium oxide synthesized by atomic layer deposition method

The work experimentally and theoretically analyzes the process of atomic layer deposition of hafnium oxide with the participation of water vapor as an oxidizing agent. The study of infrared absorption, Auger spectroscopy and luminescence shows that with increasing water pulse duration, the concentration of oxygen vacancies decreases and the composition tends to stoichiometric, which is given by the formula HfO2. Modeling of gas dynamics and kinetics of film synthesis by atomic layer deposition was performed, which showed the dependence of the coverage of the film surface with oxygen on the pulse duration and deposition temperature. A comparison of calculations with experimental results made it possible to estimate the magnitude of the kinetic coefficients of the synthesis processes that describe the observed experimental dependences and to show that the larger of the two temperatures of the atomic layer deposition window is associated with water desorption.

Circumnuclear Dust in Luminous Early-type Galaxies. I. Sample Properties and Stellar Luminosity Models

Dusty circumnuclear disks (CNDs) in luminous early-type galaxies (ETGs) show regular, dynamically cold molecular gas kinematics. For a growing number of ETGs, Atacama Large Millimeter/sub-millimeter Array (ALMA) CO imaging and detailed gas-dynamical modeling facilitate moderate-to-high precision black hole (BH) mass (M BH) determinations. From the ALMA archive, we identified a subset of 26 ETGs with estimated M BH/M ⊙ ≳ 108 to a few × 109 and clean CO kinematics but that previously did not have sufficiently high-angular-resolution near-IR observations to mitigate dust obscuration when constructing stellar luminosity models. We present new optical and near-IR Hubble Space Telescope (HST) images of this sample to supplement the archival HST data, detailing the sample properties and data-analysis techniques. After masking the most apparent dust features, we measure stellar surface-brightness profiles and model the luminosities using the multi-Gaussian expansion (MGE) formalism. Some of these MGEs have already been used in CO dynamical modeling efforts to secure quality M BH determinations, and the remaining ETG targets here are expected to significantly improve the high-mass end of the current BH census, facilitating new scrutiny of local BH mass–host galaxy scaling relationships. We also explore stellar isophotal behavior and general dust properties, finding these CNDs generally become optically thick in the near-IR (A H ≳ 1 mag). These CNDs are typically well aligned with the larger-scale stellar photometric axes, with a few notable exceptions. Uncertain dust impact on the MGE often dominates the BH mass error budget, so extensions of this work will focus on constraining CND dust attenuation.

Experimental COP optimization procedure in an air-based reverse Brayton cycle for cryogenic applications

Sustainable and efficient refrigerants are essential due to increasing regulatory constraints on traditional high-GWP refrigerants. This study investigates the potential of natural refrigerants, specifically air, in Reverse Brayton Cycles (RBC) for low-temperature applications. Unlike carbon dioxide and ammonia, which pose limitations and safety concerns below -40°C, air offers a safer and more versatile solution due to its excellent thermodynamic properties and availability. An experimental RBC was constructed using automotive components like centrifugal compressors, a radial turbine, and inter-coolers. These cost-effective and accessible components shift the refrigeration paradigm. The RBC was tested to optimize the Coefficient of Performance (COP) at -100°C while dissipating 2 kW, a typical scenario for whole-body cryotherapy (WBC). Key control parameters included the pressure ratio of the centrifugal compressors and the position of the stator vanes in the variable geometry turbine (VGT). The optimization process resulted in a COP increase of up to 28%. Additionally, a 1D gas-dynamic model validated these results, suggesting that different component selections could enhance performance by 17% compared to the experimental optimum point. Air-based RBC systems using automotive components can effectively achieve temperatures below -40°C, offering a viable, eco-friendly alternative to traditional refrigerants. This advancement addresses regulatory challenges and contributes to the scientific community by providing a sustainable refrigeration solution using commercially available components and demonstrating improvements through experimental data.

Distributionally robust risk-resistant synergistic restoration strategy for integrated electricity and gas system with high-fidelity gas dynamic modeling

A synergistic restoration strategy offers a promising solution for expediting restoration of integrated electricity and gas system (IEGS) following blackouts, particularly under the increasing energy interdependence between these two subsystems. However, achieving synergistic restoration is challenging in 1) distinct operational characteristics between electric and gas flow rates, leading to difficulties in accurately modeling the restoration processes with significantly varying system states; 2) potential risks posed by uncertainties, such as fluctuating renewable energy and random contingencies, undermining the effectiveness of restoration strategy. To address these challenges, this paper proposes a novel distributionally robust risk-resistant synergistic restoration strategy for IEGS. Firstly, to accurately capture the dynamics of slow gas flow relative to instantaneous power flow, we propose a high-fidelity linear dynamic gas flow model with multiparametric disaggregation technique, demonstrating satisfactory accuracy in restoration scenarios. Then, the risks by uncertainties of renewable energy and contingencies are handled within distributionally robust framework. Moreover, the IEGS restoration problem is reformulated as a two-stage robust optimization problem by convex conservative approximation and strong duality theory, which is solved by a nested column-and-constraint generation algorithm. Finally, simulation results validate the effectiveness of the proposed restoration strategy, showing the improved restoration efficiency, security, and risk-resistant performance.

The singular limits of the Riemann solutions as pressure vanishes for a reduced two-phase mixtures model with non-isentropic gas state

We study the cavitation and concentration phenomena of the Riemann solutions for a reduced two-phase mixtures model with non-isentropic gas state in vanishing pressure limit. We solve the Riemann problem by constructing the regions in (p, u, s) coordinate system. Then we obtain the limiting behaviors of the Riemann solutions and the formation of δ-shock waves and vacuum as pressure vanishes. We conclude that, as pressure vanishes, the limit of Riemann solutions is the Riemann solutions of the reduced 2-dimensional pressureless gas dynamics model. Finally, we present numerical simulations which are consistent with our theoretical analysis.

The Riemann problem with delta initial data with Dirac delta function in both components for a pressureless gas dynamic model

The Riemann problem with delta initial data with Dirac delta function in both components for a pressureless gas dynamic model

Gas assisted binary black hole formation in AGN discs

ABSTRACT We investigate close encounters by stellar mass black holes (BHs) in the gaseous discs of active galactic nuclei (AGNs) as a potential formation channel of binary black holes (BBHs). We perform a series of 2D isothermal viscous hydrodynamical simulations within a shearing box prescription using the Eulerian grid code Athena++. We co-evolve the embedded BHs with the gas keeping track of the energetic dissipation and torquing of the BBH by gas gravitation and inertial forces. To probe the dependence of capture on the initial conditions, we discuss a suite of 345 simulations spanning BBH impact parameter (b) and local AGN disc density (ρ0). We identify a clear region in b − ρ0 space where gas assisted BBH capture is efficient. We find that the presence of gas leads to strong energetic dissipation during close encounters between unbound BHs, forming stably bound eccentric BBHs. We find that the gas dissipation during close encounters increases for systems with increased disc density and deeper periapsis passages rp, fitting a power law such that $\Delta E \propto \rho _0^{\alpha }r_{\mathrm{p}}^{\beta }$, where {α, β} = {1.01 ± 0.04, −0.43 ± 0.03}. Alternatively, the gas dissipation is approximately ΔE = 4.3MdvHvp, where Md is the mass of a single BH minidisc just prior to the encounter when the binary separation is 2rH (two binary Hill radii), vH and vp are the relative BH velocities at 2rH and at the first closest approach, respectively. We derive a prescription for capture which can be used in semi-analytical models of AGN. We do not find the dissipative dynamics observed in these systems to be in agreement with the simple gas dynamical friction models often used in the literature.

Gas-Dynamical Model of Accretion on a Neutron Star with Viscosity and the Influence of Large-Scale Vortices on the Transmission of Angular Momentum

Gas-Dynamical Model of Accretion on a Neutron Star with Viscosity and the Influence of Large-Scale Vortices on the Transmission of Angular Momentum

Gas-dynamical Mass Measurements of the Supermassive Black Holes in the Early-type Galaxies NGC 4786 and NGC 5193 from ALMA and HST Observations* *Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated

We present molecular gas-dynamical mass measurements of the central black holes in the giant elliptical galaxies NGC 4786 and NGC 5193, based on CO (2−1) observations from the Atacama Large Millimeter/submillimeter Array (ALMA) and Hubble Space Telescope near-infrared imaging. The central region in each galaxy contains a circumnuclear disk that exhibits orderly rotation with projected line-of-sight velocities of ∼270 km s−1. We build gas-dynamical models for the rotating disk in each galaxy and fit them directly to the ALMA data cubes. At 0.″31 resolution, the ALMA observations do not fully resolve the black hole sphere of influence (SOI), and neither galaxy exhibits a central rise in rotation speed, indicating that emission from deep within the SOI is not detected. As a result, our models do not tightly constrain the central black hole mass in either galaxy, but they prefer the presence of a central massive object in both galaxies. We measure the black hole mass to be (MBH/108M⊙)=5.0±0.2[1σstatistical]−1.3+1.4[systematic] in NGC 4786 and (MBH/108M⊙)=1.4±0.03[1σstatistical]−0.1+1.5[systematic] in NGC 5193. The largest component of each measurement’s error budget is from the systematic uncertainty associated with the extinction correction in the host galaxy models. This underscores the importance of assessing the impact of dust attenuation on the inferred M BH.

Numerical study on effect of operating pressures on CRKEC-based two-stage ejector

The two-stage ejector mixing-diffuser section in this study was computed using the Redlich-Kwong equation of state. The ejector was designed based on the constant rate of kinetic energy change (CRKEC) approach. The water vapor mixing diffuser profile and flow properties were calculated using a one-dimensional gas dynamic model. For the numerical investigation, the estimated geometrical profile based on the input design and operating conditions was utilized. ANSYS-Fluent 14.0 was em-ployed for the numerical study. The analysis was conducted under both on-design and off-design scenarios using the standard k-ε turbulence model. The impact of operating factors on flow behavior and entrainment ratios was investigated at off-design conditions. The findings demonstrated that the operational total pressures of the primary, secondary, and exit flows are a function of the two-stage ejector (TSE) entrainment ratio. With a higher exit pressure and more secondary/entrained flows, the entrain-ment ratio increases. However, altering the primary flow pressure in ways other than for the design conditions reduces the entrainment ratio.

On the Construction of a Gas-Dynamic Model of Electrical Conductivity of an Ionized Gas Based on a Supercomputer Simulation of Electron Kinetics

On the Construction of a Gas-Dynamic Model of Electrical Conductivity of an Ionized Gas Based on a Supercomputer Simulation of Electron Kinetics

Water Dose influence to the ALD hafnium oxide process: Simulation and experiment

In this work, we report a two-dimensional gas-dynamic model for the formation of hafnium oxide from TDMAH and water during the atomic layer deposition (ALD) process. Application of the model is demonstrated by the example of water cycle, in which the monolayer of functional groups –OH is formed. The simulation results show that the duration of the water pulse affects the dynamics of surface coverage with the -OH groups. At short pulse durations, the resulting coverage of the film surface with -OH groups becomes incomplete and has heterogeneous distribution over the film surface, which is due to the design of the reaction chamber and regimes of gas supply. The amount of residual water vapor depends on the duration of the water pulse and pumping regimes. Experimental data show the influence of water pulse duration on the refractive index, which is related to the structure of the deposited layer (composition, morphology, etc.). Based on experimental data and modeling results, we explain the effect of water pulse duration on the refractive index by the change in reaction mechanisms depending on water amount in the chamber. With a lack of water, the incomplete monolayer of –OH groups is formed and a {HfO2-y} layer grows as a result of the monomolecular decomposition of the precursor. With an excess of water, we expect the implementation of multilayer adsorption of water, provoking the reaction of the precursor in the volume of the water film, leading to the formation of the product {HfO2+y}.

Bar-driven Gas Dynamics of M31

The large-scale gaseous shocks in the bulge of M31 can be naturally explained by a rotating stellar bar. We use gas dynamical models to provide an independent measurement of the bar pattern speed in M31. The gravitational potentials of our simulations are from a set of made-to-measure models constrained by stellar photometry and kinematics. If the inclination of the gas disk is fixed at i = 77°, we find that a low pattern speed of 16–20 km s−1 kpc−1 is needed to match the observed position and amplitude of the shock features, as shock positions are too close to the bar major axis in high Ω b models. The pattern speed can increase to 20–30 km s−1 kpc−1 if the inner gas disk has a slightly smaller inclination angle compared with the outer one. Including subgrid physics such as star formation and stellar feedback has minor effects on the shock amplitude, and does not change the shock position significantly. If the inner gas disk is allowed to follow a varying inclination similar to the H i and ionized gas observations, the gas models with a pattern speed of 38 km s−1 kpc−1, which is consistent with stellar-dynamical models, can match both the shock features and the central gas features.

The limiting behavior of Riemann solutions to the Euler equations of compressible fluid flow for the modified Chaplygin gas with the body force

In this paper, we investigate the limiting behavior of Riemann solutions to the Euler equations of compressible fluid flow for modified Chaplygin gas with the body force as the two parameters tend to zero. The formation of delta shock waves and the vacuum states is identified and analyzed during the process of vanishing pressure in the Riemann solutions. The concentration and cavitation are fundamental and physical phenomena in fluid dynamics, which can be mathematically described by delta shock waves and vacuums, respectively. In this paper, our main objective is to rigorously investigate the formation of delta shock waves and vacuums and observe the concentration and cavitation phenomena. First, the Riemann problem of the Euler equations of compressible fluid flow for the modified Chaplygin gas with the body force is solved. Second, we rigorously confirm that, as the pressure vanishes, any two shock Riemann solution to the Euler equations of compressible fluid flow for the modified Chaplygin gas with the body force tends to a δ-shock solution to the pressureless gas dynamics model with a body force, and the intermediate density between the two shocks tends to a weighted δ-measure that forms the δ-shock; any two-rarefaction-wave Riemann solution to the Euler equations of compressible fluid flow for the modified Chaplygin gas with the body force tends to a solution consisting of four contact discontinuities together with vacuum states with three different virtual velocities in the limiting situation.

High-speed synchrotron x-ray imaging and multi-physics modeling of molten pool and gas dynamics in laser additive manufacturing of a medium-entropy alloy

High-speed synchrotron x-ray imaging and multi-physics modeling of molten pool and gas dynamics in laser additive manufacturing of a medium-entropy alloy

Проблема изложения требований норм в области пожарной безопасности в России

Purpose. The success of fire extinguishment directly depends on discharging the necessary and sufficient amount of extinguishing agents onto the fire. Analysis of the characteristics of modern extinguishing agents and the research works in this area has shown that when extinguishing fires at power facilities the application of water is not always appropriate, and the specifics of using other means, such as, for example, compressed air foam, have not been fully studied. The article presents the findings of the research and mathematical modeling of fluid and gas dynamics of compressed air foam through delivery hoses when extinguishing fires at power facilities. Methods. The developed measuring system, programmes and experimental techniques have been applied in the research. Existing accurate models of mathematical evaluation of fluid and gas dynamics parameters of two-phase medium have been applied for numerical modelling. Findings. As a result of experimental study and mathematical modeling pressure loss indicators have been obtained along the hose line length when compressed air foam is supplied in a wide range of expansion from 2 to 20. The relative deviation of results has been no more than 7 %. Research application field. The obtained results and further research have practical significance in improving the efficiency of fire service units in performing firefighting tasks. Conclusions. The conducted research allowed obtaining data and their application in practical activity of firefighting units will make it possible to evaluate the capacity of firefighting units in preparing preliminary planning documents for critical facilities, including power facilities, and increase the efficiency of fire extinguishment.

Исследование динамики свободной поверхности, ограничивающей конечную массу самогравитирующего газа

The work researches the evolution of the free surface which limits the polytropic, isentropic and self-gravitating ideal gas moving in vacuum. Gas currents are described with the mathematical model of gas dynamics, constructed due to the system of nonlinear integro-differential equations, expressed in Euler coordinate system. The transformation of the given system to the Lagrangian coordinates lets reduce it to the equivalent system consisting of integral Voltair’s equations and the equation of continuity in the Lagrangian form, and also it lets break down the unknown boundaries. Free boundary is determined as a great number of points of the system of integral equations solution achieved when depicting the boundary points of the initial area within the point of the moving area. For the system there is the proved theorem of the existence and uniqueness of the solution of the Cauchy problem in the space of the infinitely differentiated functions. Methods of qualitative research of the system of gas dynamics were applied in the work for the research of the evolution of the free surface.

A computational study of time-fractional gas dynamics models by means of conformable finite difference method

<abstract> <p>This paper introduces a novel numerical scheme, the conformable finite difference method (CFDM), for solving time-fractional gas dynamics equations. The method was developed by integrating the finite difference method with conformable derivatives, offering a unique approach to tackle the challenges posed by time-fractional gas dynamics models. The study explores the significance of such equations in capturing physical phenomena like explosions, detonation, condensation in a moving flow, and combustion. The numerical stability of the proposed scheme is rigorously investigated, revealing its conditional stability under certain constraints. A comparative analysis is conducted by benchmarking the CFDM against existing methodologies, including the quadratic B-spline Galerkin and the trigonometric B-spline functions methods. The comparisons are performed using $ {L}_{2} $ and $ {L}_{\infty } $ norms to assess the accuracy and efficiency of the proposed method. To demonstrate the effectiveness of the CFDM, several illustrative examples are solved, and the results are presented graphically. Through these examples, the paper showcases the capability of the proposed methodology to accurately capture the behavior of time-fractional gas dynamics equations. The findings underscore the versatility and computational efficiency of the CFDM in addressing complex phenomena. In conclusion, the study affirms that the conformable finite difference method is well-suited for solving differential equations with time-fractional derivatives arising in the physical model.</p> </abstract>

Model for Chapman-Jouguet deflagrations in open ended tubes with varying vent ratios

We present a gas dynamic model for Chapman-Jouguet deflagrations driving a shock in tubes or congested configurations with rear venting. The model extends the previous work of Chue, Clarke and Lee (Proc. Roy. Soc. 1993) to include rear venting. Two models are formulated, one for a perfect gas with constant heat of combustion, and the second by assuming chemical equilibrium in the product gases and temperature dependent specific heats. In the presence of rear venting, much slower flames and shock strengths are generated; these are controlled by the vent ratio, which reduces the post shock strength and speed of the gas convecting the flame forward. Calculation results are presented for small hydrocarbon-air and hydrogen-air deflagrations. The results of the model are found in good agreement with the critical deflagration speed measured experimentally in large scale weakly confined congested experiments for auto-ignition insensitive mixtures. This suggests that flames in these experiments have reached their maximum Chapman-Jouguet deflagration speed prior to transition. We present a time scale estimate for flame acceleration and auto-ignition behind reflected shocks. For sensitive mixtures for which the flame acceleration time is longer than the auto-ignition time (hydrogen, acetylene), limited experimental evidence indicate transition to detonation at critical speeds lower than the CJ deflagration condition. The time scale ratio thus provides the conditions for which reaching the CJ deflagration condition can be taken as a necessary condition for DDT.