Gas Flow Field Research Articles

A sharp-interface method for the simulation of shock-induced vaporization of droplets

A sharp-interface method is developed to calculate the vaporization of droplets in high-speed flows. The levelset method is used to track the liquid-gas interface. A sharp-interface approach using an interfacial Riemann solver based ghost fluid method (RS-GFM) is developed to couple the liquid and gas flow-fields at the interface. The interfacial Riemann problem accounts for surface tension and phase change effects, which affect the jump in pressure and the normal velocity fields across the interface. The current RS-GFM also accounts for the jump in viscous stresses at the interface caused by the Marangoni effect. The resulting sharp-interface approach captures all the first-order physical effects at play in shock-induced droplet vaporization. The method is validated by comparing the current results with benchmark experimental and numerical results. Finally, 2D and 3D simulations of shock-droplet interactions are performed to quantify the shock-induced vaporization rate of the droplets, under the influence of viscosity and surface tension.

Numerical Simulation of a New Horizontal Spray Tower for Sintering Flue Gas Desulfurization

The flow rate and temperature of the flue gas from a sintering machine can fluctuate in a wide range; thus, the follow-up desulfurization facility should be operated stably and maintained on-line. A new type of horizontal spray tower, which can achieve high efficiency with low pressure loss and easy maintenance, was invented by the University of Science and Technology Beijing. A 3D multiphase computational fluid dynamics (CFD) model of the horizontal spray tower was constructed with Fluent software to study the internal flow field and the reaction of the horizontal spray tower. The standard k–ξ model and the Eulerian–Lagrangian model were adopted in this study. Results show that the flow field in the spray tower can be numerically simulated utilizing the CFD technology. The inlet angle exerts an important effect on the flue gas flow field of the horizontal tower. When the first-order efficiency and the economic indicators are taken into account, an inlet angle of 75° is recommended in the top inlet intake mode, whereas a 30° inlet angle performs the best in the side inlet intake mode. The spray configuration exerts an important influence. When the spray cone angle is 110° and the installation height is controlled at 0.8 m from the top surface, the smoke residence time is long, and the contact is sufficient. The results can provide theoretical support for the optimization of the structure of the spray tower.

Feasibility Study of an Adaptive-Pressure Plasma Coating Process—Part 1: Model Description

Thermal barrier coatings for gas turbine engines are mainly produced by electron beam physical vapor deposition or atmospheric plasma spray depending on the thermomechanical loading of engine components. This study deals with the numerical design of a two-step thermal plasma-aided physical vapor deposition process capable of efficiently evaporating the coating material processed in the plasma jet and of producing a strain-tolerant coating microstructure from vapor phase condensation. The system involved a high-pressure chamber and a low-pressure chamber connected by an expansion nozzle. The objective was to achieve the highest deposition efficiency for a given plasma specific enthalpy. The numerical simulations based on computational fluid dynamics and direct simulation Monte Carlo models projected the effect of the process geometry and operating conditions on the gas flow fields, powder vaporization efficiency and nucleation/growth phenomena in the gas phase. For a targeted powder feed rate, they allowed to determine the length of the high-pressure chamber, the diameter of the expansion nozzle and other dimensions of the deposition system. The expansion nozzle that linked the two chambers was the crucial component of the process, and the predictions made it possible to select the geometry and process operating parameters that avoided its clogging and/or melting

Influence of LOS angle on aero-optics imaging deviation

When the airborne optical system works in the atmosphere, the image received in the optical system is deviation due to the change of gas flow field outside the optical head cover. This paper studies the effect of target line-of-sight(LOS)angle on aero-optics imaging deviation. We modeled and meshed a typical blunt-nosed high-speed vehicle by GAMBIT software. The CFD calculation was carried out by using the integrated RANS solver in FLUENT software. A reverse ray tracing method and a trace stop criterion were developed for optical calculation. The light propagation path was divided into three segments: the inside of the aircraft, the non-uniform flow field outside the aircraft, and the freestream of the atmosphere. Then we studied the influence in a wide range of LOS angles from 5° to 85°. The results show that as the LOS angle increases, the non-uniform flow field density distribution on the light propagation path becomes more and more flat, the corresponding refractive index becomes smaller, and the aero-optics imaging deviation is also reduced gradually.

Numerical Studies on the Downstream Uniformity Modulation of Atmospheric Pressure Cold Plasma Jet Array via Gas Flow Controlling Strategy

Atmospheric pressure plasma jets (APPJs) have attracted considerable interests due to their low-temperature and easily controlled features. In order to cover a larger area for broader applications, spatially extended atmospheric plasma arrays are designed and constructed by a number of packed plasma jets. Despite their outstanding stability and flexibility, it remains a challenge for the jets to form large-scale uniformity on downstream substrates due to complex electrical and hydrodynamic interactions. In this paper, we use a 2-D temporally evolving code coupling electric, flow, and temperature fields, as well as chemical reactions to study synergistic effects of the multi-fields coupling on discharge and propagation characteristics of the jet array based on a USim software framework. The influence of gas flow and a substrate downstream on the plasma jets dynamics and uniformity are investigated by the model. Also, essential strategies for uniformity modulation are acquired. Results show that the balanced evolution of the ionization process and the effective merging of discharge channels could be realized by modulating the gas flow field. Therefore, a homogeneous distribution of plasma downstream can be obtained by adjusting the gas flow field properly, which provides a new efficient way for the uniformity control in the field of plasma processing.

Study of thickness distribution and dimensional accuracy of stamped metallic bipolar plates

The aim of the present paper is to fabricate metallic bipolar plates (BPPs) with active area of 100cm2 modeled on an industrial gas flow field scheme. In order to produce these plates, a stamping process has been employed to reduce cost and increase production speed. 316L stainless steel sheets with the thickness of 0.1 mm have been used. The effect of forming forces on channel filling depth, channel width, rib width, the uniformity in the depth of formed channels and the thickness distribution of channels have also been studied. The stress and strain distributions of formed bipolar plate are investigated using finite element simulation. The results reveal that the stamping process does have the ability to produce a perfect bipolar plate by one-step forming die for desired dimensions. Moreover, increasing the stamping force to an optimum level has insignificant effect on the depth of the channels. However, stamping force increment results in an increase in width of the channels and ribs.

Numerical thermofluid simulation of a decaying arc behavior in CO2/O2/C5F10O (C5‐PFK) considering more than nona‐atomic molecules

AbstractThe present article describes numerical thermofluid simulation results on decaying arc behavior in 80%CO2 + 10%O2 + 10%C5F10O (C5‐PFK) gas considering molecules constituted with more than 9 atoms in a nozzle space on the assumption of local thermodynamic equilibrium (LTE) condition. The gas mixture 80%CO2 + 10%O2 + 10%C5F10O (C5‐PFK) is one of the candidate alternatives for SF6 in a gas circuit breaker. First, we calculated 80%CO2 + 10%O2 + 10%C5F10O (C5‐PFK) arc characteristics only by considering less than 8‐atom molecules. However, it seems possible to produce more than nona‐atomic molecules in the low‐temperature region in 80%CO2 + 10%O2 + 10%C5F10O (C5‐PFK) arcs. The present work further calculated the equilibrium composition of this gas mixture at 0.1 MPa with taking account more than nona‐atomic molecules. Furthermore, their thermodynamic and transport properties were also computed with collision integrals between species considered. Using these properties, the arc temperature and gas flow fields were calculated using two‐dimensional LTE model for a free recovery condition from dc 50 to 0 A. Results showed that a similar temperature decay was obtained for arcs in the 80%CO2 + 10%O2 + 10%C5F10O (C5‐PFK) gas mixture to that for arcs in 100%CO2 gas. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Effect of active control of indoor gas flow field on the efficiency of air purifier

In this paper, it is proposed to use electric fan to actively control the indoor gas flow field to improve the ability of an air purifier to capture PM2.5 and other fine particles. For this purpose, an indoor physical model formed by a room, an air purifier and an electric fan is established and the simulation software Fluent is used to simulate the gas flow field distribution and PM2.5 particle tracking. The control method of the electric fan based on periodic rectangular wave is adopted to control and maintain the steady and conducive indoor gas flow field distribution for gathering particle pollutants into the air purifier’s inlet. The simulation results show that the active control method of gas flow field can improve the purification speed and effectiveness of air purifier, and the simulation results are verified by actual test of the purification process of PM2.5 particles in an enclosed room. It provides an economical, practical and effective method to improve indoor air quality.

Study on flow field of gas–solid two-phase pulsed jet

In this paper, a computational fluid dynamics–discrete element method (CFD–DEM) coupling method is established to simulate the starch granule injection by coupling CFD and DEM. Then a gas–solid two-phase pulsed jet system is designed to capture the flow field trajectory of particle injection (colored starch with a mean diameter of 10.67 [Formula: see text]m), and the image is processed by color moment and histogram. Finally, the simulation results are compared with the experimental results, and the following conclusions are drawn. The numerical simulation results show that with the increase of injection pressure, the injection height increases gradually. When the injection pressure reaches above 0.4 MPa, the increase of injection height decreases. The experimental images show that the larger the pressure (i.e., the greater the initial velocity), the faster the velocity of particle distribution in the space, and the injection heights with the injection pressures of 0.4 MPa and 0.5 MPa are close, which is consistent with the result from the FLUENT numerical simulation based on CFD–DEM.

Rotating discharges in a coaxial microwave plasma source under atmospheric pressure

This article reports experimental observation of rotating plasma discharges in a coaxial structure at a frequency of 2.45 GHz and under atmospheric pressure. In contrast to other cases, the discharge in our case spins without external static magnetic field or moving electrodes. Its formation and impact factors are experimentally explored. Results show that the rotating discharge, especially the peculiarities of its rotation velocity, is attributed to the combined action of gas flow and electromagnetic field intensity between the conductors. Raising the electromagnetic field intensity or reducing the gas flow rate in appropriate ranges can result in a notable increase of the rotation speed. Experiments also demonstrate that the rotation properties are independent of the coaxial dimensions. This article is supposed to provide a new thinking and guidelines for inducing rotating discharge in a coaxial structure without electrodes moving or external magnetic field.

Functional application of Fourier sine transform in radiating gas flow with non-singular and non-local kernel

Several industrial manufacturing processes mostly depend upon measurement of gases for controlling the product quality, process control, environmental compliance and production efficiencies. We propose here unsteady natural convection radiating flow as an application of gas flow measurement through mathematical modeling based on governing fractional differential equations. The mathematical model of unsteady natural convection radiating flow is analyzed by Fourier sine and Laplace transform with novel analytical calculations and results. From the analysis of mathematical point of view, the main novelty of considered technique is fractional approach of Atangana–Baleanu which provides non-singular effect of gas with Mittag–Leffler kernel, promising straightforward convergence of imposed initial and boundary conditions that is not assumed for perturbation and discretization. The analytical solutions are obtained for the temperature distribution and velocity field of gas flow based on sine and cosine sinusoidal waves, and these are expressed in terms of elementary functions. Finally, in order to meet the physical aspects of the problem, the multiple variations and differential parametric analysis have been presented through graphical illustrations.

Influence of the secondary flow control on the transverse gaseous injection flow field properties in a supersonic flow

The supersonic mixing process is a critical issue for the design of the scramjet engine. In this paper, the secondary flow control concept has been proposed and studied in order to strengthen the mixing process between the fuel and the incoming flow with the freestream Mach number being 3.75, and the influence of the secondary flow position on the mixing augmentation mechanism has been evaluated as well. The obtained results show that the secondary flow control concept has a great impact on the mixing augmentation mechanism in the transverse injection flow field, and the parameters should be properly selected, especially for the secondary flow position. When the upstream hole is close to the jet flow and the downstream hole is far away from the jet flow, the mixing process between the fuel and the incoming flow could be promoted, namely Case 1 is the best choice for the mixing augmentation in the range considered in the current study. This is due to the variation of the separation zone generated upstream of the fuel jet, and this issue should be evaluated quantitatively. The hydrogen plume shape changes from a “kidney” to a “lamp”, and it is far away from the bottom wall in Case 1. The premature ignition phenomenon could be prevented properly in Case 1.

Parametric Study of Two Stable Forms of Discharge Burning in a Hall-Effect Thruster

In this paper, we experimentally studied the behavior of the integral operation parameters of a Hall-effect thruster (thrust and specific thrust impulse) in two stable discharge glow modes significantly different from each other in anodic efficiency. The studies were conducted using a laboratory model of a Hall-effect thruster with an extended layer with an average discharge channel diameter of 77 mm in the discharge voltage range of 500–900 V and in the gas-flow rate range from 2 to 5 mg/s. The most striking distinguishing features of the observed glow regimes are the plasma jet shape and the discharge current value at almost identical input parameters (gas flow, discharge voltage, and magnetic field). In the entire studied range of input parameters when changing from the optimal mode (in terms of efficiency) to suboptimal, the main integral characteristics of the engine are shown to undergo a stepwise change: the discharge current increases by 10‒30% with a simultaneous relative drop in thrust by 5–15% and in efficiency by 20–40%. A detailed study of the anodic efficiency structure showed that, at abrupt rebuilding, the efficiency of using the electron current (the ratio of the ion current to the discharge current) changes, i.e., the electron conductivity in the engine discharge channel.

Velocity Field of Gas Flow in the External Wave Field Near an Open End of a Tube in Transition Through a Resonance Frequency

The velocity field of gas flow field has been studied under forced longitudinal oscillations of homogeneous gas in an open tube near the first natural frequency. Dependences of gas velocity in the axial direction in the external wave field at different distances from the open end of the tube have been obtained. Experimental results have been compared to theoretical calculations.

Numerical and experimental studies of gas flow in a particulate filter

Predicted gas flow fields in wall-flow particulate filters, used for vehicular emissions abatement, from both one- and three-dimensional numerical models have been validated for the first time. This has been achieved using experimental measurements made using magnetic resonance imaging (MRI). Two-dimensional MRI velocity images of isotropic spatial resolution 140 µm px−1 were acquired perpendicular to the filter channels at multiple points, allowing measurement of the gas axial velocity in both the inlet and outlet channels along the length of the filter. Consideration of the mass balance between data points permitted the through-wall (i.e. filtration) velocity to also be calculated. These velocity data were acquired at six flow rates, corresponding to channel Reynolds numbers in the range 102–1251, and compared with the predictions from both an open source three-dimensional CFD code and a recent one-dimensional model. Good agreement was observed for both models at low flow rates, but the three-dimensional model outperformed the one-dimensional model at higher flow rates. The validation of the 3D CFD method allowed its use to probe local gas hydrodynamics, specifically calculating the variation of the momentum convection correction factor and wall friction factor. Comparisons of the calculated factors and literature correlations showed the effects of flow development are significant and have not previously been considered. When these correlations were used with the 1D model, the velocity predictions were coincident with those of the 3D CFD. Hence, with the appropriate flow descriptors, the 1D model can be used to give accurate gas velocity predictions but at a fraction of the computational time required to run CFD code.

Uniformity improvement of deep silicon cavities fabricated by plasma etching with 12-inch wafer level

The formation of various deep silicon structures using plasma etching has wide applications in sensors, micro-electro-mechanical systems and 3D wafer level integration. However, the fabrication of silicon cavities with high accuracy at depth within a large wafer size is still a challenge due to the large amount of etching required. Herein, silicon cavity etching uniformity approaching 3% in a depth of ~100 µm on a 12-inch wafer is achieved through tuning the focus ring height, baffle shape, double zone helium cooling system and chamber pressure. The simulation of the electromagnetic field and gas flow field separately provides the guidance for the improvement, and the way in which the wafer temperature influences the etch uniformity is demonstrated. These results have significance for both the understanding of the plasma etching mechanism and the practical application of the silicon etching process for advanced device fabrication.

Numerical study of temperature and gas flow fields in Ar–O2 tandem-type inductively coupled thermal plasma with Ti feedstock powder injection

A numerical simulation was conducted to obtain temperature and gas flow fields in tandem-type inductively coupled thermal plasma (tandem ICTP). Tandem ICTP is formed using two coil currents (upper coil and lower coil) in a single plasma torch, that was already developed for nanoparticle synthesis. The temperature distribution of the tandem ICTP and evaporation of feedstock Ti powder were obtained for different gap lengths between the upper and lower coil and coil turn numbers. Results indicate that increasing the gap length between the upper and lower coil produces two separately controlled high-temperature areas in tandem ICTP. This result suggests that tandem ICTP provides a temperature field that is favourable for particle evaporation of injected particles while maintaining ICTP in the upper region of the plasma torch for stable operation.

CFD Analysis of Scramjet Engine Combustion Chamber with Alternating Wedge-Shaped Strut Injector at Flight Mach 6.5

This paper presents the CFD analysis for hydrogen fueled scramjet engine using alternating wedge-shaped strut injectors at flight Mach 6.5. The fuel used by alternating wedge-shaped strut injectors is hydrogen and this present work is constructed on the species transport combustion and k-epsilon turbulence model which is governed by both mixing and chemical kinetics. This turbulence model is most common in CFD for simulation of mean flow characteristics for turbulent flow conditions. This CFD analysis of scramjet engine combustion chamber is basically focused on for optimizing various flow fields of flue gases and the combustion efficiency. There is increase in temperature and pressure at the boundary walls of the combustor. The shock waves have great influences on increasing the pressure and temperature which results in increasing at the combustion rate as well as it increases the combustion efficiency. From the analysis it’s investigated that alternating wedge-shaped strut injector provides the maximum temperature and pressure of 3825K and 1650784Pa respectively.

Use of CFD to Investigate Flow Characteristics and Oil Distribution Inside an Oil-injected Screw Compressor

The well-developed CAE tools are used to investigate flow characteristics and oil distribution inside an oil-injected screw compressor. The flow field of gas mixed with oil is calculated by ANSYS CFX. TwinMesh generates high quality hexahedral grids for the compression chambers. There are two cases studied in this study. In the first case, the compressor models under four loading conditions are analyzed. The pressure curve is used to see if the designed built-in volume index is appropriate. In the second case, the compressor models under oil-free and oil-injected conditions are analyzed. The pressure gradients on rotor surfaces and velocity vector fields are used to describe the effects of lubrication and sealing in the sealing line gap, the tip gap, and the outlet end gap of rotors. The designer could optimize the slider and know if the oil is properly distributed in each gap.

Mathematical analysis of discontinuities in the flow field of gas in a cylindrical pipe using diffusion MRI

In this study, Magnetic Resonance Imaging (MRI) is used to detect partial and total blockage of hydrogen gas in a cylindrical pipe. Diffusion Magnetic Resonance (DMR) equation is solved analytically for flow of fluid in a radially symmetric cylindrical pipe. Appropriate boundary conditions were imposed and the radial axis varied to depict partial and total blockage in the pipe. The results show that for free fluid flow, the magnetization is between 0.004 and 0.005. For partial blockage, the magnetization reduces (signal loss) in value to 0.00001 and for total blockage it is zero (0). This method is a viable alternative to other methods of detecting blockage in fluid pipelines in oil and gas industry due to its noninvasive analysis of flow in fluid. The MRI model also registers signal in its first few seconds or microseconds. The analysis can also be useful in process industries where different network of pipes are used or machines use cylindrical pipes or tubes in transporting materials especially when there is a partial or total blockage at any point in the network.Keywords: Bloch NMR Equations, DMR equation, Cylindrical pipe, Magnetization