Gas Dynamics Research Articles

Limits of solutions to the Aw-Rascle traffic flow model with generalized Chaplygin gas by flux approximation

The Riemann problem for the Aw-Rascle (AR) traffic flow model with a double parameter perturbation containing flux and generalized Chaplygin gas is first solved. Then, we show that the delta-shock solution of the perturbed AR model converges to that of the original AR model as the flux perturbation vanishes alone. Particularly, it is proved that as the flux perturbation and pressure decrease, the classical solution of the perturbed system involving a shock wave and a contact discontinuity will first converge to a critical delta shock wave of the perturbed system itself and only later to the delta-shock solution of the pressureless gas dynamics (PGD) model. This formation mechanism is interesting and innovative in the study of the AR model. By contrast, any solution containing a rarefaction wave and a contact discontinuity tends to a two-contact-discontinuity solution of the PGD model, and the nonvacuum intermediate state in between tends to a vacuum state. Finally, some representatively numerical results consistent with the theoretical analysis are presented.

Synergistic effects of vapor and gaseous cavitation and mass-transfer mechanism in a mechanical pump

Dynamic gas–liquid mass-transfer processes are extensively encountered in gas–liquid mixture transport systems, where mechanical pumps pressurize the mixture and are accompanied by flow and mass-transfer instabilities. Herein, our proposed gaseous cavitation model was innovatively developed to revolutionize the independent unidirectional absorbed or evolved mass transfers. Complex gas–liquid behaviors under the synergetic effects of gaseous and vapor cavitations were achieved for the first time in an on-orbit refueling mechanical pump. Four coupled mass-transfer processes, namely, evolution, evaporation, absorption, condensation, and gas–liquid distribution, were investigated through numerical calculations. The results indicated that when the solution was close to critical saturation and conversion of the mass-transfer direction, a surge in the mass-transfer rate, and more intense hydrodynamic instability occurred. The vapor drove the accumulation of the evolved gas along the edge of the vapor in the impeller, where the evolved-dominated mass-transfer bands existed on the suction surfaces of the long blade, exhibiting the degassing characteristics of the vapor cavity, and other regions belonged to absorption-dominated region. Continuous dissolution induced by significant positive pressure gradient led to the maximum absorbed oxygen concentration at the impeller outlet. The maximal increments of absorbed oxygen in the suction chamber, impeller, and volute were 98%, 447%, and 694%, respectively, and the volume fractions were attenuated by 18.3%, 12.5%, and 5.0%, respectively. Notably, an increase in the gas volume fraction was the dominant reason for exacerbating the instability of the impeller forces, and the range of the radial force tended to be narrow and concentrated as the concentration increased.

Interacting Stark localization dynamics in a three-dimensional lattice Bose gas

Interacting Stark localization dynamics in a three-dimensional lattice Bose gas

Gas dynamics within landfast sea ice of an Arctic fjord (NE Greenland) during the spring–summer transition

Sea ice is an active component of the Earth’s climate system, interacting with both the atmosphere and the ocean. Arctic sea ice is commonly covered by melt ponds during late spring and summer, strongly affecting sea ice physical and optical properties. How melt pond formation affects sea ice gas dynamics and exchanges between sea ice and the atmosphere, with potential feedbacks on climate, is not well known. Here we measured concentrations of N2, O2, and Ar, total alkalinity, and dissolved inorganic carbon within sea ice of Young Sound, NE Greenland, to examine how melt pond formation and meltwater drainage through the ice affect its physical properties and gas composition, including impacts on CO2 exchange with the atmosphere. Sea ice gas composition was controlled mainly by physical processes, with most of the gas initially in gaseous form in the upper ice layer. A minor contribution from biological processes was associated with positive estimates of net community production (up to 2.6 µmol Lice−1 d−1), indicating that the ice was net autotrophic. As the sea ice warmed, the upper ice gas concentrations decreased, suggesting a release of gas bubbles to the atmosphere. However, as melt ponds formed, the ice surface became strongly depleted in gases. Due to melt pond development, meltwater permeated through the ice, resulting in the formation of an underwater ice layer also depleted in gases. Sea ice, including brine, slush, and melt ponds, was undersaturated in CO2 compared to the atmosphere, supporting an uptake of up to −4.26 mmol m−2 d−1 of atmospheric CO2. As melt pond formation progressed, however, this uptake weakened in the strongly altered remaining ice surface (the “white ice”), averaging −0.04 mmol m−2 d−1. This study reveals the importance of melt pond formation and dynamics for sea ice gas composition.

Metal Doping Induced Formation and Dynamic Gas Sorption of a Highly Porous Mesoporous MetalOrganic Framework

A new high-porosity MOF of [Ni2.3Zn0.7(tzba)3 (H2 O)6 ]·12DMF (NiZn-MOF) processes 2D (3,6)-grid layers constructed from rare [M2 (tz)3 (H2 O)3 ] and [M(COO)3 ] nodes. The metal doping of Ni2+ and Zn2+ are crucial for the formation of the two kinds of metal nodes and subsequent synergistical assembly into the mesoporous MOF, in contrast to the formation of MIL-88-topology resembled compound of {(Me2 NH2 )[Ni3 (μ3 -OH)(tzba)3 (H2 O)3 ]·8DMF (Ni3-MOF) using single Ni2+ as metal source. The regular 2D layers stacked in parallel and ABAB fashion through interlayer hydrogen bonding, leading to a neutral framework with void fraction up to 72.1% and 1D mesoporous hexagonal channels sized at 24.0 Å in diameter. The large gas accessible porosity was revealed by the saturated N2 and CO2 uptake of 720 and 708 cm3 g-1, at 77 K and 195 K, respectively, giving a high Langmuir surface area of 2066 m2 g-1. The varying gas sorption amounts dependent on accommodated solvents and activation temperature, as well as the gate-opening behaviors in sorption isotherms, well confirm the dynamic structure response to guest species of the flexible framework.

Stationary thermal-gas-dynamics of flows in the cylinder and exhaust system of a piston engine

THE PURPOSE. To evaluate the influence of the exhaust manifold design on gas dynamics and heat transfer of stationary, turbulent gas flows in the cylinder and the exhaust system of a reciprocating internal combustion engine for different boundary conditions based on physical and mathematical modeling.METHODS. The study of gas dynamics and heat transfer of flows was carried out using the CFD approach in specialized Russian-made software. The simulation was performed for a pressure drop from 0.15 to 40 kPa (the flow velocity at the outlet of the system was 10-130 m/s). The k-e turbulence model was used for modeling. The computational grid consisted of 610,000 cells. The design change consisted in the use of profiled channels with cross sections in the form of a circle (diameter 30 mm), a square (side 30 mm) and a triangle (side 52 mm).RESULTS. The article describes the mathematical model, the studied geometry of the exhaust system and the analysis of the obtained data. The velocity field, isolines of equal velocities, and tangential velocity vectors were chosen as the gas-dynamic characteristics of the flow. The gas dynamics in the longitudinal section of the exhaust system and the valve, as well as the visualization of the flow structure in 4 control sections along the length of the exhaust system, were analyzed. The heat transfer coefficient in the exhaust system was used to evaluate the heat transfer characteristics of the flow. Qualitative and quantitative differences in gas dynamics and heat transfer processes are shown.CONCLUSION. It has been established that there are common gas-dynamic effects during the flow of gas in different elements of the exhaust system. The evolution of the flow structure along the length of the exhaust system is shown based on the change in the velocity field, isolines of equal velocities, and tangential velocity vectors. The vortex structures formed in the valve assembly and the corners of the profiled channels are revealed. It has been established that the use of profiled channels in the exhaust system leads to a decrease in the heat transfer coefficient by 5 to 12%.

On the dynamics of dilute gases

The evolution of a gas can be described by different mathematical models depending on the scale of observation. A natural question, raised by Hilbert in his sixth problem, is whether these models provide mutually consistent predictions. In particular, for rarefied gases, it is expected that the equations of the kinetic theory of gases can be obtained from molecular dynamics governed by the fundamental principles of mechanics. In the case of hard sphere gases, Lanford (1975) has shown that the Boltzmann equation does indeed appear as a law of large numbers in the low density limit, at least for very short times. The aim of this paper is to present recent advances in the understanding of this limiting process.

Rapid and integrated petroleum systems analysis with dynamic gas fraction and flexural reconstructions: Application to hydrocarbon charge and commodity risk

The most time consuming and computationally intensive steps in petroleum systems analysis involve building heat flow boundary conditions that are consistent with regional geologic observations, solving the transient heat equation, and translating a range of hydrocarbon charge predictions from source intervals into prospect specific predictions that can be used for decision making in oil and gas exploration. Furthermore, three-dimensional regional flexure, which can have a significant impact on paleo-migration pathways, often is not included in the critical step of translating charge calculations into trap specific predictions due to the time-consuming nature of map preparation. In this paper, an efficient and integrated petroleum systems analysis (IPA) workflow is presented with a new fast, semi-analytical, decoupled approach for solving the transient heat equation that is fully integrated with a rapid inversion methodology for transient heat flow boundary conditions and a 3D regional flexural reconstruction that uses standard basin modeling inputs and requires little to no additional map preparation. A charge-to-trap model is also described that translates hydrocarbon expulsion calculations with dynamic parameterized gas fractions that vary with transformation ratio into trap specific predictions using flexurally restored migration polygons. This fully integrated and efficient approach enables rapid interactive investigation of uncertainty space and fast probabilistic modeling that is ideal for evaluating hydrocarbon charge and commodity risk in data-sparse frontier basins. The applicability of this approach is demonstrated for assessing charge and commodity risk with a case study from the Colorado Basin, Argentina, whereby two alternative hydrocarbon accumulation hypotheses that postulate that traps are filled to structural spill with undersaturated oil are tested for reservoirs located in the upper Colorado Formation that are charged by postulated Aptian and Neocomian source rocks. This application indicates that it is unlikely that the tested traps are filled to structural spill with undersaturated oil, and how incorrect conclusions on hydrocarbon commodity may be reached if 3D regional flexure is not considered during petroleum systems analysis. Finally, it is also shown how this integrated and efficient approach can be implemented with low-cost computational platforms such as Python Anaconda or in spreadsheet programs that empower modelers to rapidly translate their ideas into benchmarked prototypes that can be immediately leveraged by the geoscience community (www.github.com/eakneller/ipatoolkit3D).

Investigation of a horizontal low power wind turbine

THE PURPOSE. Development and creation of an experimental stand, carrying out a full-scale experiment, verification the numerical model of a NREL S809 airfoil based on its dimensionless characteristics, analyze the flow around the airfoil at different angles of attack.METHODS. A technique for studying the flow structure around a wind turbine using numerical methods of gas dynamics based on solving the system of Navier-Stokes equations is considered. Mathematical modeling methods were used using the k-ε and SST turbulence model.RESULTS. In this study, a laboratory stand is designed using CAD systems and created using additive FDM printing technologies An experimental study of the dependence of the rotation speed on the blade angle and the resulting voltage in the electric system, the change in the power factor and efficiency of a wind power plant depending on the wind speed was carried out.CONCLUSION. The developed wind turbine has a power of 2.6 W at a wind speed of 4 m / s. This invention is recommended for the purpose of teaching methods of design and construction of similar installations. For the developed wind turbine, it is possible to optimize the work using the method of numerical three-dimensional thermogasdynamic modeling, to evaluate the nature of the flow at off-design operating modes, which speeds up the process of creating the final installation and improves its efficiency parameters.

Preparation and Analysis of Experimental Findings on the Thermal and Mechanical Characteristics of Pulsating Gas Flows in the Intake System of a Piston Engine for Modelling and Machine Learning

Today, reciprocating internal combustion engines are used in many branches of the economy (power engineering, machine engineering, transportation, and others). In order for piston engines to meet stringent environmental and economic regulations, it is necessary to develop complex and accurate control systems for the physical processes in engine elements based on digital twins, machine learning, and artificial intelligence algorithms. This article is aimed at preparing and analysing experimental data on the gas dynamics and heat transfer of pulsating air flows in a piston engine’s intake system for modelling and machine learning. The key studies were carried out on a full-scale model of a single-cylinder piston engine under dynamic conditions. Some experimental findings on the gas-dynamic and heat-exchange characteristics of the flows were obtained with the thermal anemometry method and a corresponding measuring system. The effects of the inlet channel diameter on the air flow, the intensity of turbulence, and the heat transfer coefficient of pulsating air flows in a piston engine’s inlet system are shown. A mathematical description of the dependences of the turbulence intensity, heat transfer coefficient, and Nusselt number on operation factors (crankshaft speed, air flow velocity, Reynolds number) and the inlet channel’s geometric dimensions are proposed. Based on the mathematical modelling of the thermodynamic cycle, the operational and environmental performance of a piston engine with intake systems containing channels with different diameters were assessed. The presented data could be useful for refining engineering calculations and mathematical models, as well as for developing digital twins and engine control systems.

The Spatiotemporal Dynamic Impact Mechanism of Soil Greenhouse Gases under Precipitation Based on Environmental Law

There is a chain reaction between precipitation patterns and atmospheric greenhouse gases. Understanding the impact mechanism of the spatiotemporal dynamics of soil greenhouse gases under precipitation changes is of great significance, allowing for a more accurate assessment of soil greenhouse gas budgets under future precipitation patterns. In view of this, the research uses sensors to collect environmental sample data and gas concentration data, using Conv-LSTM to achieve data analysis. The research also introduces the kernel DM model to optimize the gas distribution modeling problem. Compared to manual periodic monitoring or gas monitoring using a single mobile robot, the gas distribution model used in this study is innovative. The innovation lies in its ability to capture global gas flow trends in data sampling and predictive analysis. The results show that when soil moisture changes between 5% and 35%, the soil carbon dioxide gas flux after the water addition treatment takes a 20% soil moisture level as the inflection point, showing a trend of first increasing, and then decreasing. This indicates that the mathematical model proposed in this study is effective in collecting and analyzing environmental data.

Station-keeping strategy for tethered drag sail-based transverse formation

During general 2-satellite formation, the relative baseline between satellites periodically changes, resulting in limited time for interferometric imaging and poor observation quality. This study incorporates a drag sail into the tethered satellite system, where the chief satellite moves in a low Earth orbit (LEO) and connected deputy drag sail is in a non-Keplerian displaced orbit. Given the free-molecule flow property of the atmosphere in LEO, the drag sail can simultaneously provide normal pressure and tangential stress. By adjusting its attitude appropriately, the sail can move synchronously with the chief satellite with respect to a fixed relative position, during which a fixed baseline for formation flying can be achieved. Because the component of the baseline perpendicular to the ground tracks of the satellite is constant, the proposed system is denoted as a transverse formation. To better investigate the system, the nonlinear characteristics are analyzed for the controlled dynamical models. Considering the complexity of aerodynamic force based on rarefied gas dynamics, feasible formation configurations are investigated from the perspective of the control force direction. Then, a control strategy is provided to maintain the formation configuration based on the linear quadratic regulator (LQR) control framework. The parameter optimization of LQR control considers the coupling degree of modals, control force, and error. The attitude of the sail is inversely computed based on the Taylor expansion, and the results show that the proposed maintenance strategy is successfully realized with the smooth rotation of the drag sail.

Vehicle refrigeration modification using an ejector: Optimization and exergoeconomic analysis

BackgroundAdvances in technology in recent years have increased energy consumption which has led to global warming. In line with the Paris agreement, the optimal use of energy is a way to overcome the issue. Air conditioning and refrigeration systems are among the sectors that account for a large share of energy consumption. This has elicited the implementation of optimization of refrigeration systems. MethodIn this research, the aim is to utilize the radiator waste heat of an engine with a volume of 2000 cc in an ejector refrigeration cycle as an alternative to conventional refrigeration cycles in vehicles. For this purpose, the ejector refrigeration cycle is modeled with energy, exergy, and eco-exergy equations and the ejector is modeled with dynamic gas equation. After modeling, effective parameters, namely, condenser outlet temperature, inlet temperature and pressure to the secondary nozzle, and inlet temperature to the primary nozzle are optimized using TOPSIS multi-objective optimization method. The selected objectives were reducing system capital investment cost, and increasing, COP, and the ejector performance (ω) criterion. ResultsIt was found that the ejector refrigeration cycle reduces the electric power and capital investment cost by 0.743 kW and 0.0028 $/h, respectively, and also increases the COP by 0.917 compared to the conventional refrigeration systems in the vehicle.

Flow-controlled expiration reduces positive end-expiratory pressure requirement in dorsally recumbent, anesthetized horses.

Equine peri-anesthetic mortality is higher than that for other commonly anesthetized veterinary species. Unique equine pulmonary pathophysiologic aspects are believed to contribute to this mortality due to impairment of gas exchange and subsequent hypoxemia. No consistently reliable solution for the treatment of peri-anesthetic gas exchange impairment is available. Flow-controlled expiration (FLEX) is a ventilatory mode that linearizes gas flow throughout the expiratory phase, reducing the rate of lung emptying and alveolar collapse. FLEX has been shown to improve gas exchange and pulmonary mechanics in anesthetized horses. This study further evaluated FLEX ventilation in anesthetized horses positioned in dorsal recumbency, hypothesizing that after alveolar recruitment, horses ventilated using FLEX would require a lower positive end-expiratory pressure (PEEP) to prevent alveolar closure than horses conventionally ventilated. Twelve adult horses were used in this prospective, randomized study. Horses were assigned either to conventional volume-controlled ventilation (VCV) or to FLEX. Following induction of general anesthesia, horses were placed in dorsal recumbency mechanically ventilated for a total of approximately 6.5 hours. Thirty-minutes after starting ventilation with VCV or FLEX, a PEEP-titration alveolar recruitment maneuver was performed at the end of which the PEEP was reduced in decrements of 3 cmH2O until the alveolar closure pressure was determined. The PEEP was then increased to the previous level and maintained for additional three hours. During this time, the mean arterial blood pressure, pulmonary arterial pressure, central venous blood pressure, cardiac output (CO), dynamic respiratory system compliance and arterial blood gas values were measured. The alveolar closure pressure was significantly lower (6.5 ± 1.2 vs 11.0 ± 1.5 cmH2O) and significantly less PEEP was required to prevent alveolar closure (9.5 ± 1.2 vs 14.0 ± 1.5 cmH2O) for horses ventilated using FLEX compared with VCV. The CO was significantly higher in the horses ventilated with FLEX (37.5 ± 4 vs 30 ± 6 l/min). We concluded that FLEX ventilation was associated with a lower PEEP requirement due to a more homogenous distribution of ventilation in the lungs during expiration. This lower PEEP requirement led to more stable and improved cardiovascular conditions in horses ventilated with FLEX.

3D hydrodynamics simulations of internal gravity waves in red giant branch stars

ABSTRACT We present the first 3D hydrodynamics simulations of the excitation and propagation of internal gravity waves (IGWs) in the radiative interiors of low-mass stars on the red giant branch (RGB). We use the ppmstar explicit gas dynamics code to simulate a portion of the convective envelope and all the radiative zone down to the hydrogen-burning shell of a $1.2\, {\rm M}_{\odot }$ upper RGB star. We perform simulations for different grid resolutions (7683, 15363, and 28803), a range of driving luminosities, and two different stratifications (corresponding to the bump luminosity and the tip of the RGB). Our RGB tip simulations can be directly performed at the nominal luminosity, circumventing the need for extrapolations to lower luminosities. A rich, continuous spectrum of IGWs is observed, with a significant amount of total power contained at high wavenumbers. By following the time evolution of a passive dye in the stable layers, we find that IGW mixing in our simulations is weaker than predicted by a simple analytical prescription based on shear mixing and not efficient enough to explain the missing RGB extra mixing. However, we may be underestimating the efficiency of IGW mixing given that our simulations include a limited portion of the convective envelope. Quadrupling its radial extent compared to our fiducial set-up increases convective velocities by up to a factor 2 and IGW velocities by up to a factor 4. We also report the formation of a $\sim 0.2\, H_P$ penetration zone and evidence that IGWs are excited by plumes that overshoot into the stable layers.

Optimization of lower air inlet tube configuration for maximizing burner efficiency based on gas dynamics, and heat transfer potency in a Rotary Hearth Furnace

Optimization of lower air inlet tube configuration for maximizing burner efficiency based on gas dynamics, and heat transfer potency in a Rotary Hearth Furnace

Investigation of Low-Frequency Noise, in Order to Reduce it During the Operation of Compressor Mounts

Experimental researches of characteristic of low frequency noise and gas dynamic gas pressure pulsations were carried out on experimental compressor mount and in the real industrial conditions. It is shown that gas pressure pulsations are making the main contribution into forming of low frequency noise of compressor mount. New device of reduction of low frequency noise and dynamic pressure pulsations was suggested. The device is allowing us to reach simultaneous efficient reduction of noise and pressure pulsations during operation of compressor mounts and to reduce the risk of the accidents in industrial conditions.

Sustainable Lifecycle of Perforated Metal Materials.

In an era of rapidly growing consumer demand and the subsequent development of production, light materials and structures with a wide range of applications are becoming increasingly important in the field of construction and mechanical engineering, including aerospace engineering. At the same time, one of the trends is the use of perforated metal materials (PMMs). They are used as finishing, decorative and structural building materials. The main feature of PMMs is the presence of through holes of a given shape and size, which makes it possible to have low specific gravity; however, their tensile strength and rigidity can vary widely depending on the source material. In addition, PMMs have several properties that cannot be achieved with solid materials; for example, they can provide considerable noise reduction and partial light absorption, significantly reducing the weight of structures. They are also used for damping dynamic forces, filtering liquids and gases and shielding electromagnetic fields. For the perforation of strips and sheets, cold stamping methods are usually used, carried out on stamping presses, particularly using wide-tape production lines. Other methods of manufacturing PMMs are rapidly developing, for example, using liquid and laser cutting. An urgent but relatively new and little-studied problem is the recycling and further efficient use of PMMs, primarily such materials as stainless and high-strength steels, titanium, and aluminum alloys. The life cycle of PMMs can be prolonged because they can be repurposed for various applications such as constructing new buildings, designing elements, and producing additional products, making them more environmentally friendly. This work aimed to overview sustainable ways of PMM recycling, use or reuse, proposing different ecological methods and applications considering the types and properties of PMM technological waste. Moreover, the review is accompanied by graphical illustrations of real examples. PMM waste recycling methods that can prolong their lifecycle include construction technologies, powder metallurgy, permeable structures, etc. Several new technologies have been proposed and described for the sustainable application of products and structures based on perforated steel strips and profiles obtained from waste products during stamping. With more developers aiming for sustainability and buildings achieving higher levels of environmental performance, PMM provides significant environmental and aesthetic advantages.

Effects of Aeration on Surface Water Nutrient Dynamics and Greenhouse Gas Emission in Different Straw Returning Paddy Fields

Straw returning is of great significance for improving soil structure, soil fertility, crop yield, and quality. However, straw returning causes environmental problems such as increased methane emission and non-point source pollutant emission risk. How to reduce the negative effects of straw returning is an urgent problem to be solved.In this study, the effects of aerobic treatment on carbon and nitrogen concentration in surface water and greenhouse gas emissions in paddy fields with different treatments of straw returning were systematically compared.The results showed that different treatments of straw returning significantly increased chemical oxygen demand (COD) in the surface water of the paddy field and significantly promoted the methane emission of the rice field and the global warming potential (GWP), although it slightly reduced N2O emission. The increasing trends showed that wheat straw returning>rape straw>broad bean straw returning.Straw returning increased rice yield when compared with the control without straw returning, but the difference was not significant. Aerobic treatment reduced the COD in surface water by 15%-32%, the methane emission of the paddy field by 10.4%-24.8%, and the GWP of paddy field by 9.7%-24.4% under different straw returning treatments, without affecting the rice yield. The mitigation effect of aerobic treatment with wheat straw returning was the best. The results indicated the potential of oxygenation measures in greenhouse gas emission mitigation and COD emission risk reduction in straw returning paddy fields, especially in wheat straw returning paddy fields.

Dynamics of direct impact accretion in degenerate binary systems

ABSTRACTWe consider the gas dynamics in an accreting binary system of degenerate stars within the framework of the Newtonian approximation. In such a system, the accretion stream can impact the surface of a white dwarf (WD) or neutron star (NS) as a result of the very compact orbit. This causes a loss of angular momentum from the orbit and spin-up of the accretor. We construct an approximation for the specific angular momentum of the accreting matter, which goes to spin up the accretor and approximations for some other parameters of the system. It is shown that the obtained approximation of the specific momentum is qualitatively different from the widely used Keplerian formula. It should affect the boundary between scenarios of immediate tidal disruption and slow mass-loss of the donor in WD–WD and NS–NS binaries, as well as the time of stable mass transfer in the stripping scenario.