Gas Dynamics Research Articles

Deep smoothness weighted essentially non-oscillatory method for two-dimensional hyperbolic conservation laws: A deep learning approach for learning smoothness indicators

In this work, we enhance the fifth-order Weighted Essentially Non-Oscillatory (WENO) shock-capturing scheme by integrating deep learning techniques. We improve the established WENO algorithm by training a compact neural network to dynamically adjust the smoothness indicators within the WENO scheme. This modification boosts the accuracy of the numerical results, particularly in proximity to abrupt shocks. Notably, our approach eliminates the need for additional post-processing steps, distinguishing it from previous deep learning-based methods. We substantiate the superiority of our new approach through the examination of multiple examples from the literature concerning the two-dimensional Euler equations of gas dynamics. Through a thorough investigation of these test problems, encompassing various shocks and rarefaction waves, our novel technique consistently outperforms the traditional fifth-order WENO scheme. This superiority is especially evident in cases where numerical solutions exhibit excessive diffusion or overshoot around shocks.

Asymptotic preserving methods for quasilinear hyperbolic systems with stiff relaxation: a review

Hyperbolic systems with stiff relaxation constitute a wide class of evolutionary partial differential equations which describe several physical phenomena, ranging from gas dynamics to kinetic theory, from semiconductor modeling to traffic flow. Peculiar features of such systems is the presence of a small parameter that determines the smallest time scale of the system. As such parameter vanishes, the system relaxes to a different one with a smaller number of equations, and sometime of a different mathematical nature. The numerical solution of such systems may present some challenges, in particular if one is interested in capturing all regimes with the same numerical method, including the one in which the small parameter vanishes (relaxed system). The design, analysis and application of numerical schemes which are robust enough to solve this class of systems for arbitrary value of the small parameter is the subject of the current paper. We start presenting different classes of hyperbolic systems with relaxation, illustrate the properties of implicit–explicit (IMEX) Runge–Kutta schemes which are adopted for the construction of efficient methods for the numerical solution of the systems, and then illustrate how to apply IMEX schemes for the construction of asymptotic preserving schemes, i.e. scheme which correctly capture the behavior of the systems even when the relaxation parameter vanishes.

The Riemann problem for the Chaplygin gas dynamics with a single-point heating source

This paper is devoted to the Riemann solutions to the Chaplygin gas dynamics with a single-point heating source. To deal with Dirac measure source term, we transform this model into a system of conservation laws and then present a definition of solution to this system of conservation laws. Based on this definition, we establish, respectively, the condition for the occurrence of stationary contact discontinuity solution and delta standing wave solution. With the help of these results, by analyzing the possible combination of various waves, ten kinds of exact solutions and the criteria for the emergence of each solution are established. It is observed that a delta standing wave solution arises for certain initial values, where two components of this solution contain the Dirac measure. It is also noticed that a stationary contact discontinuity followed by a delta shock wave emerges in some solutions. Moreover, these solutions can be used to test the validation of numerical algorithm for a system of conservation laws with a singular source term.

Kinematic signatures of planet–disk interactions in vertical shear instability-turbulent protoplanetary disks

Context. Planets are thought to form inside weakly ionized regions of protoplanetary disks, where turbulence creates ideal conditions for solid growth. However, the nature of this turbulence is still uncertain. In fast cooling parts of this zone the vertical shear instability (VSI) can operate, inducing a low level of gas turbulence and large-scale gas motions. Resolving the kinematic signatures of active VSI could reveal the origin of turbulence in planet-forming disk regions. However, an exploration of kinematic signatures of the interplay between VSI and forming planets is needed for a correct interpretation of radio interferometric observations. A robust detection of VSI would lead the way to a deeper understanding of the impact of gas turbulence on planet formation. Aims. The objective of this study is to explore the effect of VSI on the disk substructures triggered by an embedded fairly massive planet. We focus on the impact of this interplay on CO kinematic observations with the ALMA interferometer. Methods. We conducted global 3D hydrodynamical simulations of VSI-unstable disks with and without embedded massive planets, exploring Saturn- and Jupiter-mass cases. We studied the effect of planets on the VSI gas dynamics, and made a comparison with viscous disks. Post-processing the simulations with a radiative transfer code, we examined the kinematic signatures expected in CO molecular line emission, varying disk inclination. Further, we simulated deep ALMA high-resolution observations of our synthetic images, to test the observability of VSI and planetary signatures. Results. The embedded planet produces a damping of the VSI along a radial region, most effective at the disk midplane. For the Saturn case, the VSI modes are distorted by the planet’s spirals producing mixed kinematic signatures. For the Jupiter case, the planet’s influence dominates the overall disk gas kinematics. Conclusions. The presence of massive planets embedded in the disk can weaken the VSI large-scale gas flows, limiting its observability in CO kinematic observations with ALMA.

Interactions between elementary waves and weak discontinuity in two-layer blood flow through artery

Blood flow through arterial circulation can be characterized by fluid transport in flexible tubes and modeled mathematically using the conservation of mass and momentum. A one-dimensional model for two-layer blood flow with different blood velocities and the same constant density in each layer derived from the Euler equations of gas dynamics by taking the vertical average across each layer. This work presents interactions of elementary waves with a weak discontinuity for the quasilinear 3 × 3 system of conservation laws governing the two-layer blood flow in arteries. Exploiting elementary waves as a single-parameter curve, we study the Riemann solution uniquely and consequently establish the condition on initial data for the existence of a solution to the Riemann problem. Furthermore, we discuss the evolution of weak discontinuity waves and subsequently derive their amplitudes; in what follows, we investigate the interactions of weak discontinuity with contact discontinuity and shocks. Finally, a series of numerical tests have been performed to understand the impact of shock strength and the initial data on the amplitudes of reflected and transmitted waves and the jumps in shock acceleration.

Explosions in Roche-lobe Distorted Stars: Relativistic Bullets in Binaries

State-of-the-art surveys reveal that most massive stars in the Universe evolve in close binaries. Massive stars in such systems are expected to develop aspherical envelopes due to tidal interactions and/or rotational effects. Recently, it was shown that point explosions in oblate stars can produce relativistic equatorial ring-like outflows. Moreover, since stripped-envelope stars in binaries can expand enough to fill their Roche lobes anew, it is likely that these stars die with a greater degree of asphericity than the oblate spheroid geometry previously studied. We investigate the effects of this asymmetry by studying the gas dynamics of axisymmetric point explosions in stars in various stages of filling their Roche lobes. We find that point explosions in these pear-shaped stars produce transrelativistic ejecta that coalesce into bullets pointed both toward and away from the binary companion. We present this result and comment on key morphological differences between core-collapse explosions in spherical versus distorted stars in binary systems, effects on gravitational wave sources, and observational signatures that could be used to glean these explosion geometries from current and future surveys.

A high-efficiency adaptive TENO scheme with optimal accuracy order for compressible flow simulation

In this paper, we propose a new adaptive cut-off function and develop a fifth-order targeted ENO scheme that achieves optimal accuracy at any order of critical points, which performs excellently in conventional compressible gas dynamics. The cut-off value CT is crucial for controlling the dissipation in TENO schemes. Adjusting CT can improve shock capture and increase dissipation for small-scale features. To address this issue, Fu et al. [27] and Peng et al. [28] developed the TENO-A and TENO-LAD schemes, respectively, with adaptive cut-off values CT. However, these adaptive cutoffs CT are computationally expensive due to additional free parameters and complexity. Furthermore, all TENO schemes, including the adaptive versions, can suffer from loss of accuracy at higher-order critical points. In this paper, a new adaptive cut-off function is proposed that uses a global smoothness indicator correction so that it can be automatically tuned between 0 and a given positive constant λd, ensuring that the new TENO scheme achieves optimal accuracy in smooth regions and good shock-capturing in the less smooth parts. A series of benchmark simulations demonstrate that the presented scheme provides optimal accuracy, better robustness, resolution, and numerical stability, and higher resolution than existing TENO schemes while improving computational efficiency. Due to the simplicity of the new cut-off structure, it can be easily extended to improve other TENO schemes.Program files associated to this article may be found at https://github.com/fourhairs/cfd.

THE IMPACT OF TECHNICAL SAFETY AND INTEGRITY VERIFICATION ON PROJECT DELIVERY AND ASSET PERFORMANCE

The oil and gas industry operates within a stringent regulatory framework and faces inherent risks associated with complex operations. Technical safety and integrity verification processes play a critical role in ensuring compliance with regulatory standards, minimizing risks, and enhancing asset performance. This review analyzes the influence of rigorous safety and integrity verification on project timelines, cost efficiency, and overall asset performance in the oil and gas industry. Safety and integrity verification processes encompass a comprehensive assessment of design, construction, and operational phases of oil and gas projects. These processes involve rigorous inspections, testing, and verification activities to ensure that assets meet regulatory requirements and industry standards. By adhering to these processes, operators can mitigate safety risks, prevent accidents, and safeguard human lives, as well as protect the environment. Moreover, rigorous safety and integrity verification contribute to efficient project delivery by identifying potential hazards and deficiencies early in the project lifecycle. Through proactive risk assessment and mitigation, operators can address issues promptly, thereby minimizing delays and cost overruns. Additionally, adherence to safety and integrity standards instills confidence among stakeholders, investors, and regulatory authorities, fostering trust and credibility in project execution. Furthermore, the impact of technical safety and integrity verification extends beyond project delivery to asset performance throughout its operational lifespan. Assets subjected to thorough safety and integrity verification processes exhibit higher reliability, availability, and operational efficiency. By identifying and addressing potential failure points, operators can prolong asset lifespan, optimize maintenance schedules, and reduce unplanned downtime. In conclusion, rigorous safety and integrity verification processes significantly influence project timelines, cost efficiency, and overall asset performance in the oil and gas industry. By prioritizing safety and integrity throughout the project lifecycle, operators can enhance operational excellence, mitigate risks, and achieve sustainable long-term success in the dynamic and challenging oil and gas landscape.
 Keywords: Impact, Technical Safety, Integrity Verification, Project Delivery, Asset Performance.

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.

Hungry or Not: How Stellar-Mass Black Holes Grow (or Don’t) in Dark Matter Mini-Haloes at High-Resolution

Abstract We compare the performance of the popular Bondi-Hoyle-Lyttleton (BHL) accretion scheme with a simple mass-flux scheme applied to stellar-mass black holes (BHs) across six levels of increasing spatial resolution. Simulating the formation of black holes within cosmological mini-haloes at z ∼ 20, we investigate scenarios both with and without supernova events, which result in BHs of initial mass 10.8 M⊙ and 270 M⊙ respectively. Our explicit focus on the stellar-mass range pushes the maximum resolution down to sub-10−3 pc regimes, where more complicated gas dynamics are resolved. We observe efficient growth and rotationally supported, ∼10−1 pc-scale discs around all 270 M⊙ BHs independent of resolution and accretion scheme, though clumps, bars, and spiral arm structures impact stability at high resolution. We analyse the effect of these instabilities on the accretion cycle. In contrast, all bar one of the 10.8 M⊙ BHs fail to attract a disc and experience modest growth, even when characteristic scales of accretion and dynamical friction are reasonably resolved. While the two accretion schemes somewhat converge in mass growth for the 270 M⊙ case over 1 Myr, the greater degree of gas fragmentation induces more randomness in the evolution of the 10.8 M⊙ BHs. We conclude that early universe black holes of MBH ∼ 101 M⊙ struggle to grow even in gas-rich environments without feedback in comparison to seeds of MBH ∼ 102 M⊙, and the latter exhibit convergent growth histories across accretion schemes below a resolution of dx = 1 × 10−3pc.

Low traces of acetone detection with WO3-based chemical sensors

This work presents the ability of WO3-based sensors to detect low traces of acetone, specifically within the range of 0.25–5 ppm, specific to the in-field atmosphere. The WO3 powder was synthesised through the hydrothermal method. Morpho-structural investigations showed a monoclinic structure and a good crystallization of the WO3 powder, containing well-grown and faceted grains along low-index crystallographic planes. The paste obtained by mixing the powder with propanediol was screen-printed as a thick layer onto commercial alumina substrates, obtaining the chemical sensors. A dynamic computer-controlled Gas Mixing System was utilized to ensure controlled airflow with variable relative humidity and acetone concentrations. The sensor response was explained based on physico-chemical equations, taking into consideration pre-adsorbed species of oxygen and water, both of which are relevant constituents of atmospheric conditions. The results highlight the applicative potential of WO3, having a good signal-to-noise ratio in relative humidity conditions up to 90% and a pronounced sensitive selectivity to acetone.

Spectroastrometric Survey of Protoplanetary Disks with Inner Dust Cavities

We present high-resolution spectra and spectroastrometric (SA) measurements of fundamental rovibrational CO emission from nine nearby (≲300 pc) protoplanetary disks where large inner dust cavities have been observed. The emission-line profiles and SA signals are fit with a slab disk model that allows the eccentricity of the disk and intensity of the emission to vary as power laws. Six of the sources are well fit with our model, and three of these sources show asymmetric line profiles that can be fit by adopting a nonzero eccentricity. The three other sources have components in either their line profile or SA signal that are not captured by our disk model. Two of these sources (V892 Tau and CQ Tau) have multi-epoch observations that reveal significant variability. CQ Tau and AB Aur have CO line profiles with centrally peaked components that are similar to line profiles which have been interpreted as evidence of molecular gas arising from a wide-angle disk wind. Alternatively, emission from a circumplanetary disk could also account for this component. The interpretations of these results can be clarified in the future with additional epochs that will test the variability timescale of these SA signals. We discuss the utility of using high-resolution spectroscopy for probing the dynamics of gas in the disk and the scenarios that can give rise to profiles that are not fit with a simple disk model.

Labile dissolved organic matter (DOM) and nitrogen inputs modified greenhouse gas dynamics: A source-to-estuary study of the Yangtze River

Although rivers are increasingly recognized as essential sources of greenhouse gases (GHG) to the atmosphere, few systematic efforts have been made to reveal the drivers of spatiotemporal variations of dissolved GHG (dGHG) in large rivers under increasing anthropogenic stress and intensified hydrological cycling. Here, through a source-to-estuary survey of the Yangtze River in March (spring) and October (autumn) of 2018, we revealed that labile dissolved organic matter (DOM) and nitrogen inputs remarkably modified the spatiotemporal distribution of dGHG. The average partial pressure of CO2 (pCO2), CH4 and N2O concentrations of all sampling sites in the Yangtze River were 1015 ± 225 μatm, and 87.5± 36.5 nmol L−1, and 20.3 ± 6.6 nmol L−1, respectively, significantly lower than the global average. In terms of longitudinal and seasonal variations, higher GHG concentrations were observed in the middle-lower reach in spring. The dominant drivers of spatiotemporal variations in dGHG were labile, protein-like DOM components and nitrogen level. Compared with the historical data of dGHG from published literature, we found a significant increase in N2O concentrations in the Yangtze River during 2004–2018, and the increasing trend was consistent with the rising riverine nitrogen concentrations. Our study emphasized the critical roles of labile DOM and nitrogen inputs in driving the spatial hotspots, seasonal variations and annual trends of dGHG. These findings can contribute to constraining the global GHG budget estimations and controls of GHG emission in large rivers in response to global change.

1,2-dichlorobenzene gas-phase adsorption onto Nd3+ exchanged faujasite 13X beads - Influence of the exchange rate on adsorbed amounts and desorption temperatures

Aromatic chlorinated compounds, such as 1,2-dichlorobenzene, are considered as precursors of dioxin formation and their removal from flue gas using adsorption technology could be a solution. Faujasite type zeolites seem to be the most promising adsorbent, as the size of its porosity matches the size of the molecule. Even though the cationic faujasites are hydrophilic, the strength of interaction of chlorinated aromatic compounds adsorbed in porosity are higher than with more silicic faujasite such as FAU-NaY.FAU-NaX commercial beads have been Nd3+ exchanged at different rates. Dichlorobenzene dynamic gas adsorption has been performed via a thermobalance with vapours at concentration of 938 ppm in nitrogen gas flow and the quantities absorbed have been recorded during time. Then, from the coupling of a thermobalance with an in-line mass spectrometer, the desorbed quantities and desorption temperatures have been measured for both water and dichlorobenzene.Total quantities of 1,2-dichlorobenzene adsorbed onto partially exchanged FAU-Nd-NaX zeolites increases with the exchange rate: it has been measured a capacity of 23.3 wt % (relative to activated zeolite) for the most exchanged FAU-Nd-NaX at exchange rate of 53.6 %. For that zeolite, 74.7 % of the 1,2-dichlorobenzene is adsorbed at high-energy bonds with cations, desorbable at temperatures higher than 160 °C. The desorption temperature of dichlorobenzene decreases from 380 to 310 °C for FAU-NaX and the FAU-Nd-NaX at exchange rate of 53.6 % and remains higher than that of water. So that, thermal-desorption remains a separative process between water and chlorinated molecules previously adsorbed on cationic faujasites.

Quench dynamics of a Tonks-Girardeau gas in one dimensional anharmonic trap

The quench dynamics of strongly interacting bosons on quartic and sextic traps are studied by exactly solving the time-dependent many-boson Schrödinger equation numerically. The dynamics are addressed by the key measures of one-body density in conjugate space and information entropy. For both cases, rich many-body dynamics are exhibited and the loss of the Bose–Fermi oscillation in the Tonks–Girardeau limit is also attributed.

Multiphysics Modeling for Combustion Instability in Paraffin-Fueled Hybrid Rocket Engines

The use of paraffin-based fuels is a promising approach to a low regression rate in hybrid rocket engines, and the capability to describe and predict combustion instability in the presence of liquefying fuels becomes an enabling step towards the application of hybrid rockets in a wide range of space transportation systems. In this work, a multiphysics model having this purpose is presented and discussed. The model is based on a network of submodels in which chamber gas dynamics is described by a quasi-1D Euler model for reacting flows while thermal diffusion in the grain is described by the 1D heat equation in the radial direction. An artificial neural network is introduced to reduce the computational cost required by the chemical submodel. A sensitivity analysis is performed to identify the key parameters, which have the largest influence on combustion instability and to evaluate the predictive capability of the model despite the uncertainty introduced with the necessary modeling simplifications. Results are presented considering two test cases with different oxidizers: hydrogen peroxide and gaseous oxygen. The procedure shows good agreement with the experimental results available in the literature.

Development and Validation of a Compressible Reacting Gas-Dynamic Flow Solver for Supersonic Combustion

An approach based on the OpenFOAM library has been developed to solve a high-speed, multicomponent mixture of a reacting, compressible flow. This work presents comprehensive validation of the newly developed solver, called compressibleCentralReactingFoam, with different supersonic flows, including shocks, expansion waves, and turbulence–combustion interaction. The comparisons of the simulation results with experimental and computational data confirm the fidelity of this solver for problems involving multicomponent high-speed reactive flows. The gas dynamics of turbulence–chemistry interaction are modeled using a partially stirred reactor formulation and provide promising results to better understand the complex physics involved in supersonic combustors. A time-scale analysis based on local Damköhler numbers reveals different regimes of turbulent combustion. In the core of the jet flow, the Damköhler number is relatively high, indicating that the reaction time scale is smaller than the turbulent mixing time scale. This means that the combustion is controlled by turbulent mixing. In the shear layer, where the heat release rate and the scalar dissipation rate have the highest value, the flame is stabilized due to finite rate chemistry with small Damköhler numbers and a limited fraction of fine structure. This solver allows three-dimensional gas dynamic simulation of high-speed multicomponent reactive flows relevant to practical combustion applications.

Analysis of constituent factors affecting the state of dedusting of aspiration emissions

A significant part of industry is occupied by technology that is involved in the processes of manufacturing products, for example, sanitary ware factory, foundry, chemical or sugar industry. At such enterprises a large amount of dusty air is generated, which comes from various technological processes. Dust and gas collecting devices are used to purify dusty air. Depending on the state of dust and air flow, its fraction, dust dispersion and the method of collection, different aspiration devices are used. Aspiration devices are divided by the method of dust collection into wet or dry. Each of these types of aspiration devices has its own advantages and disadvantages, which are discussed in this article, such as increased aerodynamic or hydraulic resistance, regeneration of the device, the size of the trapped fraction, the need to use flushing fluid, etc. The classification of plant types for selection to a specific process or needs depends on the most efficient method of collection, particle dispersion and energy efficiency of the dust collector. Wet dust collectors have more diverse forms, designs and applications than dry dust collectors. Wet dust collectors are divided into groups depending on the state of the liquid phase (devices in which dust deposition occurs on a film of liquid, foam devices, turbulent dust collectors or condensation devices) and on the method of dispersion of the liquid (nozzle scrubbers, devices in which crushing is carried out due to the energy of the gas-air flow or dynamic gas washers). In this article, the designs and operating features of various wet dust collectors of each of these groups are considered in accordance with their characteristics of dust collection, liquid flow rate and design shortcomings. On the basis of the works of a number of researchers, the characteristics of the fractional degree of air purification from dust are graphically presented to determine the most effective apparatus for capturing fine fractions. The conclusions are made and further tasks and plans for conducting the necessary experiments and analysis of the data of scientists' works are set.

Isothermal Limit of Entropy Solutions of the Euler Equations for Isentropic Gas Dynamics

Isothermal Limit of Entropy Solutions of the Euler Equations for Isentropic Gas Dynamics

Modeling and Fundamental Dynamics of Vacuum, Gas, and Antisolvent Quenching for Scalable Perovskite Processes.

Hybrid perovskite photovoltaics (PVs) promise cost-effective fabrication with large-scale solution-based manufacturing processes as well as high power conversion efficiencies. Almost all of today's high-performance solution-processed perovskite absorber films rely on so-called quenching techniques that rapidly increase supersaturation to induce a prompt crystallization. However, to date, there are no metrics for comparing results obtained with different quenching methods. In response, the first quantitative modeling framework for gas quenching, anti-solvent quenching, and vacuum quenching is developed herein. Based on dynamic thickness measurements in a vacuum chamber, previous works on drying dynamics, and commonly known material properties, a detailed analysis of mass transfer dynamics is performed for each quenching technique. The derived models are delivered along with an open-source software framework that is modular and extensible. Thereby, a deep understanding of the impact of each process parameter on mass transfer dynamics is provided. Moreover, the supersaturation rate at critical concentration is proposed as a decisive benchmark of quenching effectiveness, yielding ≈ 10-3 - 10-1s-1 for vacuum quenching, ≈ 10-5 - 10-3s-1 for static gas quenching, ≈ 10-2 - 100s-1 for dynamic gas quenching and ≈ 102s-1 for antisolvent quenching. This benchmark fosters transferability and scalability of hybrid perovskite fabrication, transforming the "art of device making" to well-defined process engineering.