Simulation Of Gas Flow Research Articles

Global existence and long time behavior of the ellipsoidal-Fokker–Planck equation

ABSTRACTThe ellipsoidal-Fokker–Planck (ES-FP) model is proposed recently to obtain the correct Prandtl number in the numerical simulation of rarefied gas flows, which also satisfies the same properties as the Boltzmann equation, such as the H-theorem and the conservation laws of the mass, momentum, and energy. In this paper, we consider the Cauchy problem for this ES-FP equation in , and prove the global existence of the unique solution and establish its algebraic time convergence rate to the equilibrium state.

Simulation of Gas Flow in an Anti-Surge Valve by the ANSYS CFX Software Complex

Computer simulation of gas flow in an anti-surge valve for two designs of the valve, one with single-stage separator and the other with two-stage separator with transitional cavity, is performed. Unevenness of the mass flow of gas through the series of separator passages is discovered. It is established that this unevenness is lower in a valve with two-stage separator, leading to the conclusion that such valves are efficient for gaspumping compressor systems.

Adaptive refinement strategies for the simulation of gas flow in networks using a model hierarchy

A model hierarchy that is based on the one-dimensional isothermal Euler equations of fluid dynamics is used for the simulation and optimisation of natural gas flow through a pipeline network. Adaptive refinement strategies have the aim of bringing the simulation error below a prescribed tolerance while keeping the computational costs low. While spatial and temporal stepsize adaptivity is well studied in the literature, model adaptivity is a new field of research. The problem of finding an optimal refinement strategy that combines these three types of adaptivity is a generalisation of the unbounded knapsack problem. A refinement strategy that is currently used in gas flow simulation software is compared to two novel greedy-like strategies. Both a theoretical experiment and a realistic gas flow simulation show that the novel strategies significantly outperform the current refinement strategy with respect to the computational cost incurred.

Explosion Characteristics of Hydrogen for CFD Modelling and Simulation of Turbulent Gas Flow

Renewable energies became more and more important in the last years. Hydrogen as a promising energy carrier is a perfect candidate to supply the energy demand of the world. The state of the hydrogen gas (turbulences and point concentrations) has a significant impact on the gas explosion indices. A gas cloud is formed by a partial-pressure method in gas explosion experiments in the spherical 20.0∙10-3 m3 chamber. Gas in the chamber reaches an uniform state beyond in hundreds of ms. The absolute pressure for gas dispersion should be higher than 0.01 MPa for the H2 of concentration larger than 30 vol. % of fuel. The initial temperature also influences turbulent gas flow before ignition, especially in the case of the gases lighter-than-air.

Thermal load non-uniformity estimation for superheater tube bundle damage evaluation

Industrial boiler damage is a common phenomenon encountered in boiler operation which usually lasts several decades. Since boiler shutdown may be required because of localized failures, it is crucial to predict the most vulnerable parts. If damage occurs, it is necessary to perform root cause analysis and devise corrective measures (repairs, design modifications, etc.). Boiler tube bundles, such as those in superheaters, preheaters and reheaters, are the most exposed and often the most damaged boiler parts. Both short-term and long-term overheating are common causes of tube failures. In these cases, the design temperatures are exceeded, which often results in decrease of remaining creep life. Advanced models for damage evaluation require temperature history, which is available only in rare cases when it has been measured and recorded for the whole service life. However, in most cases it is necessary to estimate the temperature history from available operation history data (inlet and outlet pressures and temperatures etc.). The task may be very challenging because of the combination of complex flow behaviour in the flue gas domain and heat transfer phenomena. This paper focuses on estimating thermal load non-uniformity on superheater tubes via Computational Fluid Dynamics (CFD) simulation of flue gas flow including heat transfer within the domain consisting of a furnace and a part of the first stage of the boiler.

Space-time discontinuous Galerkin method for the numerical simulation of viscous compressible gas flow with the k-omega turbulence model

In this article we deal with the numerical simulation of the non-stationary compressible turbulent flow described by the Reynolds-Averaged Navier-Stokes (RANS) equations. This RANS system is equipped with two-equation k-omega turbulence model. The discretization of these two systems is carried out separately by the space-time discontinuous Galerkin method. This method is based on the piecewise polynomial discontinuous approximation of the sought solution in space and in time. We use the numerical experiments to demonstrate the applicability of the shown approach. All presented results were computed with the own-developed code.

Моделирование течения излучающего газа около возвращаемого космического аппарата

Моделирование течения излучающего газа около возвращаемого космического аппарата

Analysis of gas dynamics in a single-phase two-channel plasma torch at cold blowing and considering the interaction with the electric arc

This article is devoted to the simulation of cold gas purge and flow taking into account the plasma arc in the channels of a single-phase two-channel high-voltage plasma torch with cylindrical electrodes. The results obtained in the process of modeling made it possible to simplify the model for further modeling, which will result in the distribution of velocities, temperatures and voltage drop on the arc depending on the time.

Investigations on clean and efficient remote cutting and ablating processes

Remote processes with brilliant continuous wave lasers enable highly efficient laser processes. When cutting and abrading metal or composite materials, a large amount of particles and emissions arise. In general the emissions will be exhausted. But a high amount of substances contaminates the treated part as well as the laser machine equipment and is a high health risk for the machine operator. Based on this challenge, scientific investigations were done during laser structuring with high power fiber lasers. The generated particles and emissions were evaluated and classified. To minimize the part decontaminations new air knife – cross jet solutions were tested and optimized using gas and particle flow simulations. The results of this work support the user of remote processes in guaranteeing the health and environmental regulations.

Acceleration of Gas Reservoir Simulation Using Proper Orthogonal Decomposition

High-precision and high-speed reservoir simulation is important in engineering. Proper orthogonal decomposition (POD) is introduced to accelerate the reservoir simulation of gas flow in single-continuum porous media via establishing a reduced-order model by POD combined with Galerkin projection. Determination of the optimal mode number in the reduced-order model is discussed to ensure high-precision reconstruction with large acceleration. The typical POD model can achieve high precision for both ideal gas and real gas using only 10 POD modes. However, acceleration of computation can only be achieved for ideal gas. The obstacle of POD acceleration for real gas is that the computational time is mainly occupied by the equation of state (EOS). An approximation method is proposed to largely promote the computational speed of the POD model for real gas flow without decreasing the precision. The improved POD model shows much higher acceleration of computation with high precision for different reservoirs and different pressures. It is confirmed that the acceleration of the real gas reservoir simulation should use the approximation method instead of the computation of EOS.

Numerical simulation of pressure relief gas flow under mining conditions

Numerical simulation of pressure relief gas flow under mining conditions

A new boundary scheme for simulation of gas flow in kerogen pores with considering surface diffusion effect

Navier–Stokes (NS) equations with no-slip boundary conditions fail to realistically describe micro-flows with considering nanoscale phenomena. Particularly, in kerogen pores, slip-flow and surface diffusion are important. In this study, we propose a new slip boundary scheme for the lattice Boltzmann (LB) method through the non-equilibrium extrapolation scheme to simulate the slip-flow considering surface diffusion effect. Meanwhile, the second-order slip velocity can be taken into account. The predicted characteristics in a two-dimensional micro-flow, including slip-velocity, velocity distribution along the flow direction with/without surface diffusion are present. The results in this study are compared with available analytical and reference results, and good agreements are achieved.

Using Optical Methods to Image Shockwaves in Low-Pressure Areas in Order to Increase Accuracy of Simulations of Gas Flows within Low-Pressure Areas

The area of a shockwave is the most specific area of a supersonic gas flow because its general shape is affected not only by the gas itself but also by the pressure difference between the operating (input) pressure and the atmospheric (output) pressure and by the shape of the aperture or jet the gas passes through. Simulating a supersonic gas flow leaving a jet into a high-pressure area requires to use specific constant values depending on the type of the gas and boundary conditions, which were already experimentally verified. However, when simulating a supersonic gas flow entering a low-pressure (or vacuum) area, different constant values are needed. This paper deals with a possibility of using optical methods for displaying a shockwave within a low-pressure area in order to modify a numerical model of the flow to make the simulated shockwave match the one from experiment.

Multi-scale Fractured Coal Gas–Solid Coupling Model and Its Applications in Engineering Projects

With coal mining entering the geological environment of “high stress, rich gas, strong adsorption and low permeability,” the difficulty of joint coal and gas extraction clearly augments, the risk of solid–gas coupling dynamic disasters greatly increases, and the underlying mechanisms become more complex. In this paper, based on the characteristics of coal’s multi-scale structure and spatiotemporal variation, the multi-scale fractured coal gas–solid coupling model (MSFM) was built. In this model, the interaction between coal matrix and its fractures and the mechanical characteristics of gas-bearing coal were considered, as well as their coupling relationship. By MATLAB software, the stress–damage–seepage numerical computation programs were developed, which were applied into Comsol Multiphysics to simulate gas flow caused by coal mining. The simulation results showed the spatial variability of coal elastic modulus and cross-flow behaviors of coal seam gas, which were superior to the results of traditional gas–solid coupling model. And the numerical results obtained from MSFM were closer to the measured results in field, while the computation results of traditional model were slightly higher than the measured results. Furthermore, the MSFM in a large scale was verified by field engineering project.

Study of Gaseous Sample Ionization by Excited Particles Formed in Glow Discharge Using High-Resolution Orthogonal Acceleration Time-of-Flight Mass Spectrometer

The experimental results of a mass spectral analysis of volatile organic compounds in a gaseous sample, obtained using an original design of an ion source based on the Penning ionization of a gas sample by excited metastable inert gas atoms, are presented. Using ANSYS software, a gas-dynamic simulation of reagent gas flow from discharge zone to ionization region was carried out to analyze the effect of gas flow profile on the transport of metastable atoms and ionization efficiency. The n-octane and toluene samples diluted with helium at 100 ppb mole concentrations were used for our experiments. The resulting mass spectra of n-octane and toluene samples containe far more intensive molecular ions in comparison to n-octane and toluene electron ionization mass spectra from the NIST database. The sensitivity of 5 ions per 1 pg and 130 ions per 1 pg was achieved for n-octane and toluene molecular ions using the developed ion source combined with our mass spectrometer. The corresponding detection limits are 2.3 pg s–1 for n-octane molecular ions and 0.08 pg s–1 for toluene molecular ions. The detection limit for the reported ion source was considered theoretically.

A continuous stochastic model for non-equilibrium dense gases

While accurate simulations of dense gas flows far from the equilibrium can be achieved by direct simulation adapted to the Enskog equation, the significant computational demand required for collisions appears as a major constraint. In order to cope with that, an efficient yet accurate solution algorithm based on the Fokker-Planck approximation of the Enskog equation is devised in this paper; the approximation is very much associated with the Fokker-Planck model derived from the Boltzmann equation by Jenny et al. [“A solution algorithm for the fluid dynamic equations based on a stochastic model for molecular motion,” J. Comput. Phys. 229, 1077–1098 (2010)] and Gorji et al. [“Fokker–Planck model for computational studies of monatomic rarefied gas flows,” J. Fluid Mech. 680, 574–601 (2011)]. The idea behind these Fokker-Planck descriptions is to project the dynamics of discrete collisions implied by the molecular encounters into a set of continuous Markovian processes subject to the drift and diffusion. Thereby, the evolution of particles representing the governing stochastic process becomes independent from each other and thus very efficient numerical schemes can be constructed. By close inspection of the Enskog operator, it is observed that the dense gas effects contribute further to the advection of molecular quantities. That motivates a modelling approach where the dense gas corrections can be cast in the extra advection of particles. Therefore, the corresponding Fokker-Planck approximation is derived such that the evolution in the physical space accounts for the dense effects present in the pressure, stress tensor, and heat fluxes. Hence the consistency between the devised Fokker-Planck approximation and the Enskog operator is shown for the velocity moments up to the heat fluxes. For validation studies, a homogeneous gas inside a box besides Fourier, Couette, and lid-driven cavity flow setups is considered. The results based on the Fokker-Planck model are compared with respect to benchmark simulations, where good agreement is found for the flow field along with the transport properties.

Characteristics of shale nanopore system and its internal gas flow: A case study of the lower Silurian Longmaxi Formation shale from Sichuan Basin, China

The gas flow in shale nanopores undergoes a transition from continuum-transition flow regimes to Knudsen diffusion, rather than the traditional Darcy flow, due to the dynamic properties of shale gas. Thus, becoming the premise in understanding gas flow regime within the shale nanopores to further investigate how shale permeability evolves during gas depletion as well as to predict gas production. The microstructure features of Longmaxi Formation shale (Longmaxi Shale), characterized by SEM imaging, MICP, and gas adsorption, are dominated by micropores and mesopores that are less than 10 nm in size on average. Judging from the pore sizes of Longmaxi Shale and the general reservoir pressures, the gas flow inside shale matrix is determined as slip flow and transition flow regimes by Knudsen number. About the investigation of the Barnett Shale, a second-order slip model is superior to the first-order slip model in describing apparent permeability of Longmaxi Shale. Then and there, the velocity profile and volumetric flow rate in Longmaxi Shale are discussed with a second-order slip model. The gas velocity on the pore walls becomes larger as pressure decreases. The gas production enhancement due to gas slippage effect brings about a higher yield than that of Darcy's Law. However, shale itself is highly heterogeneous in pore geometry. Therefore, the model construction of gas flow simulation must be based on refined shale pore models.

Rapid Formation of Black Holes in Galaxies: A Self-limiting Growth Mechanism

Abstract We present high-quality fluid dynamical simulations of isothermal gas flows in a rotating barred potential. We show that a large quantity of gas is driven right into the nucleus of a galaxy when the model lacks a central mass concentration, but the inflow stalls at a nuclear ring in comparison simulations that include a central massive object. The radius of the nuclear gas ring increases linearly with the mass of the central object. We argue that bars drive gas right into the nucleus in the early stages of disk galaxy formation, where a nuclear star cluster and perhaps a massive black hole could be created. The process is self-limiting, however, because inflow stalls at a nuclear ring once the mass of gas and stars in the nucleus exceeds ∼1% of the disk mass, which shuts off rapid growth of the black hole. We briefly discuss the relevance of these results to the seeding of massive black holes in galaxies, the merger model for quasar evolution, and the existence of massive black holes in disk galaxies that lack a significant classical bulge.

Flow Simulations in a Pebble Bed Reactor by a Combined DEM-CFD Approach

This paper presents computational fluid dynamics (CFD) gas flow simulations within a segment of the pebble bed core. The realistic packing structure in an entire pebble bed reactor (PBR) is produced by a means of discrete element method. The packing structure in the segment of the PBR core is then obtained. The gas flow through the voids formed by the packed pebbles is computed by CFD. It is found that the packing structure of pebbles in the PBR is crucial to CFD simulation results. On the other hand, in our numerical simulations both large eddy simulation and Reynolds-Averaged Navier-Stokes models are employed to study the effects of different turbulence models on gas flow field and relevant heat transfer. The calculations indicate the complex flow structure within the voids among the pebbles, which play the key role in heat transfer predictions.

Study of Wind Effects on Unique Buildings

The article deals with a numerical simulation of wind effects on the building of the Church of the Intercession of the Holy Virgin in the village Bulzi of the Chelyabinsk region. We presented a calculation algorithm and obtained pressure fields, velocity fields and the fields of kinetic energy of a wind stream, as well as streamlines. Computational fluid dynamic (CFD) evolved three decades ago at the interfaces of calculus mathematics and theoretical hydromechanics and has become a separate branch of science the subject of which is a numerical simulation of different fluid and gas flows as well as the solution of arising problems with the help of methods that involve computer systems.This scientific field which is of a great practical value is intensively developing. The increase in CFD-calculations is caused by the improvement of computer technologies, creation of multipurpose easy-to-use CFD-packagers that are available to a wide group of researchers and cope with various tasks. Such programs are not only competitive in comparison with physical experiments but sometimes they provide the only opportunity to answer the research questions. The following advantages of computer simulation can be pointed out:a) Reduction in time spent on design and development of a model in comparison with a real experiment (variation of boundary conditions).b) Numerical experiment allows for the simulation of conditions that are not reproducible with environmental tests (use of ideal gas as environment).c) Use of computational gas dynamics methods provides a researcher with a complete and ample information that is necessary to fully describe different processes of the experiment.d) Economic efficiency of computer calculations is more attractive than an experiment.e) Possibility to modify a computational model which ensures efficient timing (change of the sizes of wall layer cells in accordance with the chosen turbulence model).