scholarly journals Numerical Analysis of the Correlation between Arc Plasma Fluctuation and Nanoparticle Growth–Transport under Atmospheric Pressure

Nanomaterials ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 1736 ◽  
Author(s):  
Masaya Shigeta ◽  
Manabu Tanaka ◽  
Emanuele Ghedini
Keyword(s):  
Temperature Fluctuation ◽  
Dynamic Instability ◽  
Fluid Dynamic ◽  
Computational Cost ◽  
Plasma Temperature ◽  
Particle Growth ◽  
Accurate Method ◽  
Arc Plasma ◽  
Particle Distributions ◽  
Plasma Fluctuation

A time-dependent two-dimensional (2D) axisymmetric simulation was conducted for arc plasma with dynamically fluctuating fluid generating iron nanoparticles in a direct-current discharge condition. The nonequilibrium process of simultaneous growth and transport of nanoparticles is simulated using a simple model with a low computational cost. To ascertain fluid dynamic instability and steep gradients in plasma temperature and particle distributions, a highly accurate method is adopted for computation. The core region of the arc plasma is almost stationary, whereas the fringe fluctuates because of fluid dynamic instability between the arc plasma and the shielding gas. In the downstream region, the vapor molecules decrease by condensation. The nanoparticles decrease by coagulation. These results suggest that both of the simultaneous processes make important contributions to particle growth. The fluctuation of nanoparticle number density in a distant region exhibits stronger correlation with the temperature fluctuation at the plasma fringe. The correlation analysis results suggest that the distribution of growing nanoparticles distant from the arc plasma can be controlled via control of temperature fluctuation at the arc plasma fringe.

An accurate method to include lubrication forces in numerical simulations of dense Stokesian suspensions

2015 ◽  
Vol 769 ◽  
pp. 369-386 ◽  
Author(s):  
A. Lefebvre-Lepot ◽  
B. Merlet ◽  
T. N. Nguyen
Keyword(s):  
Short Range ◽  
Degrees Of Freedom ◽  
Computational Cost ◽  
Parameter Tuning ◽  
Accurate Method ◽  
Spherical Particles ◽  
Particle Model ◽  
Stokesian Dynamics ◽  
New Feature ◽  
The Many

We address the problem of computing the hydrodynamic forces and torques among $N$ solid spherical particles moving with given rotational and translational velocities in Stokes flow. We consider the original fluid–particle model without introducing new hypotheses or models. Our method includes the singular lubrication interactions which may occur when some particles come close to one another. The main new feature is that short-range interactions are propagated to the whole flow, including accurately the many-body lubrication interactions. The method builds on a pre-existing fluid solver and is flexible with respect to the choice of this solver. The error is the error generated by the fluid solver when computing non-singular flows (i.e. with negligible short-range interactions). Therefore, only a small number of degrees of freedom are required and we obtain very accurate simulations within a reasonable computational cost. Our method is closely related to a method proposed by Sangani & Mo (Phys. Fluids, vol. 6, 1994, pp. 1653–1662) but, in contrast with the latter, it does not require parameter tuning. We compare our method with the Stokesian dynamics of Durlofsky et al. (J. Fluid Mech., vol. 180, 1987, pp. 21–49) and show the higher accuracy of the former (both by analysis and by numerical experiments).

scholarly journals A Closed-Loop Optimized System with CFD Data for Liquid Maldistribution Model

Processes ◽  
2020 ◽  
Vol 8 (11) ◽  
pp. 1332
Author(s):  
Wei Zhang ◽  
Liyi Li ◽  
Baoping Zhang ◽  
Xin Xu ◽  
Jian Zhai ◽  
...  
Keyword(s):  
Closed Loop ◽  
Cfd Simulation ◽  
Fluid Dynamic ◽  
Structural Parameters ◽  
Computational Cost ◽  
Pso Algorithm ◽  
Oil Refining ◽  
Support Vector ◽  
Cfd Validation ◽  
Liquid Distributor

For the simulation of a trickle-bed reactor (TBR) in coal and oil refining, modeling the liquid maldistribution of the gas-liquid distributor incurs enormous pre-processing work and bears a huge computational cost. A closed-loop optimized system with computational fluid dynamic (CFD) data is therefore proposed for the first time in this paper. A fast prediction model based on support vector regression (SVR) is developed to simplify the modeling of the liquid flow rate in TBRs. The model uses CFD simulation results to determine an optimized set of structural parameters for the gas-liquid distributor in TBRs. In order to obtain an accurate SVR model quickly, the particle swarm optimization (PSO) algorithm is employed to optimize the SVR parameters. Then, the structural parameters corresponding to the minimum liquid maldistribution factor are calculated using the response surface methodology (RSM) based on the hybrid PSO-SVR model. The CFD validation results show a good agreement with the values predicted by RSM, with liquid maldistribution factors of 0.159 and 0.162, respectively.

A Method to Evaluate the Sensitivity of Aerodynamic Damping to Mode Shape Perturbations

2019 ◽  
Author(s):  
Jing Li ◽  
Suryarghya Chakrabarti ◽  
Wei-Min Ren
Keyword(s):  
Mode Shape ◽  
Gas Turbines ◽  
Fluid Dynamic ◽  
Computational Cost ◽  
Assessment Process ◽  
Mode Shapes ◽  
Shape Sensitivity ◽  
Aerodynamic Damping ◽  
Damped System ◽  
Cfd Analyses

Abstract Turbomachinery blade mode shapes are routinely predicted by finite element method (FEM) programs and are then used in unsteady computational fluid dynamic (CFD) analyses to predict the aerodynamic damping. This flutter stability assessment process is critical for the last-stage blades (LSBs) of modern heavy-duty gas turbines (HDGTs) which can be particularly susceptible to flutter. Evidences suggest that actual mode shapes may deviate from the FEM predictions due to changes in the FEM boundary or loading conditions, effects of the nonlinear friction contacts, and blade-to-blade variations (mistuning), among others. This uncertainty in the mode shape is accompanied by a general lack of knowledge on the sensitivity of the aerodynamic damping to a small change in mode shape. This paper presents a method to perturb a mode shape and estimate the corresponding change in aerodynamic damping in a framework enabled by linear theories and a rigid-body, quasi-3D treatment of mode shapes. This method is of low computational cost and is suitable for use in the preliminary design cycle. The numerical validation and applications of the method are demonstrated on two LSB blades. Results suggest that the mode shape sensitivity can be substantial and may even exceed the change in aerodynamic damping of a frictionally damped system when subjected to various levels of excitation.

Real Gas Effects in Turbomachinery Flows: A Computational Fluid Dynamics Model for Fast Computations

2004 ◽  
Vol 126 (2) ◽  
pp. 268-276 ◽  
Author(s):  
Paolo Boncinelli ◽  
Filippo Rubechini ◽  
Andrea Arnone ◽  
Massimiliano Cecconi ◽  
Carlo Cortese
Keyword(s):  
Fluid Dynamic ◽  
Computational Cost ◽  
Three Dimensional ◽  
Industrial Applications ◽  
Design Tool ◽  
Navier Stokes ◽  
Computational Time ◽  
Real Gas ◽  
Real Gas Effects ◽  
Low Computational Cost

A numerical model was included in a three-dimensional viscous solver to account for real gas effects in the compressible Reynolds averaged Navier-Stokes (RANS) equations. The behavior of real gases is reproduced by using gas property tables. The method consists of a local fitting of gas data to provide the thermodynamic property required by the solver in each solution step. This approach presents several characteristics which make it attractive as a design tool for industrial applications. First of all, the implementation of the method in the solver is simple and straightforward, since it does not require relevant changes in the solver structure. Moreover, it is based on a low-computational-cost algorithm, which prevents a considerable increase in the overall computational time. Finally, the approach is completely general, since it allows one to handle any type of gas, gas mixture or steam over a wide operative range. In this work a detailed description of the model is provided. In addition, some examples are presented in which the model is applied to the thermo-fluid-dynamic analysis of industrial turbomachines.

The Performance of Plasma and Multi-Physical Fields in DC Arc Plasma Reactor for CVD Diamond Film

2016 ◽  
Vol 852 ◽  
pp. 1140-1146
Author(s):  
Xiao Jing Li ◽  
Yong Liang Gao ◽  
Yan Yin ◽  
Shun Qi Zheng ◽  
Yang Sheng Zheng
Keyword(s):  
Diamond Film ◽  
Gas Flow ◽  
Plasma Reactor ◽  
Plasma Temperature ◽  
Chemical Vapor ◽  
Cvd Diamond ◽  
Arc Plasma ◽  
Cvd Diamond Film ◽  
Physical Fields ◽  
Dc Arc

Numerical simulation method was developed to investigate the performance of plasma and multi-physical fields in direct current (DC) arc plasma reactor for chemical vapor deposition (CVD) Diamond film,in order to obtain more information on the process of CVD. Finite Volume Method (FVM) was adopted. Continuous arc forming and the dynamic formation process of rotating arc plasma were shown in this paper. Multi-physics field in deposition chamber were modeled including flow field, temperature field. Distribution of velocity and temperature were obtained by solving momentum and energy equation with SIMPLE separation algorithm. Simulation results show that, plasma temperature near the cathode tip is the highest, which is more than 1×104K. The plasma distribution shape like the bell jar. The changing regularity of outlet velocity, temperature and static pressure with the distance from the anode center were revealed. The effectiveness of plasma temperature and gas flow calculated was confirmed by the experimental results. The research results provide the theoretical foundation for obtaining uniform diamond thick film.

Failure of Safety Valves Due to Flow-Induced Vibration

1980 ◽  
Vol 102 (1) ◽  
pp. 112-118 ◽  
Author(s):  
J. T. Coffman ◽  
M. D. Bernstein
Keyword(s):  
Dynamic Instability ◽  
Safety Valve ◽  
Fluid Dynamic ◽  
Coupling Mechanism ◽  
Flow Induced Vibration ◽  
Pipe Elbow ◽  
Valve Placement ◽  
Experience Survey ◽  
Future Work ◽  
Design Guidance

Flow-induced sonic vibration in boiler safety valve nozzles led to premature valve wear and failure. The valves were mounted just downstream of a 1 1/2D pipe elbow, in contravention of guidelines suggesting an 8 to 10 diameter separation to avoid sonic vibrations. Initial modifications proved unsuccessful. A consultant then recommended replacing the cylindrical valve nozzles with reducers, which stopped the vibration. A review of flow-induced cavity vibrations is presented. In the case of the safety valves the vibration is believed due to fluid-dynamic instability of the cavity shear layer, enhanced and controlled by the resonant characteristics of the adjacent cavity. The precise feedback, or coupling, mechanism that sustains the oscillation is unknown. Possible reasons for the success of the tapered shape reducer are discussed. The limited design guidance available for safety valve placement is reviewed. Results of a safety valve vibration experience survey are presented and discussed. A two-parameter guideline for safety valve placement is suggested, involving steam velocity in addition to valve location. Possible future work on safety vibration is outlined.

Simulations of Unsteady Valve Systems

2005 ◽  
Author(s):  
V. Ahuja ◽  
A. Hosangadi ◽  
P. A. Cavallo ◽  
R. J. Ungewitter ◽  
J. D. Shipman
Keyword(s):  
Dynamic Instability ◽  
Fluid Dynamic ◽  
Control Valve ◽  
Industrial Facilities ◽  
Control Valves ◽  
Grid Adaption ◽  
Instability Modes ◽  
Multi Phase Flow ◽  
Valve Operation ◽  
Multi Phase

The safe and reliable operation of industrial facilities and high pressure test stands for engine and component testing is largely dependent on the smooth performance of control valves. However, such valves frequently experience pressure oscillations from hydrodynamic instabilities, cavitation and unsteady valve operation. In this paper, we present a series of high fidelity computational simulations of control valves primarily to understand the physics associated with the dominant instability modes. A generalized multi-element framework with sub-models for grid adaption, grid movement and multi-phase flow dynamics was used to carry out the simulations. We discuss the methodology in detail with the example of transient analyses of a gaseous hydrogen control valve and capture the fluid dynamic instability that results from valve operation. Additionally, we provide detailed analyses of a modal instability that is observed in the operation of a pressure regulator valve. In both cases, the instabilities are not localized and manifest themselves as a system wide phenomena leading to oscillations in mass flow and/or undesirable chatter.

scholarly journals Verification, Validation, and Testing of Kinetic Mechanisms of Hydrogen Combustion in Fluid-Dynamic Computations

2012 ◽  
Vol 2012 ◽  
pp. 1-11 ◽  
Author(s):  
Victor P. Zhukov
Keyword(s):  
Hydrogen Oxidation ◽  
Fluid Dynamic ◽  
Computational Cost ◽  
Kinetic Scheme ◽  
Time Step ◽  
Kinetic Schemes ◽  
Ignition Delay Times ◽  
Ansys Cfx ◽  
Kinetic Mechanisms ◽  
The Impact

A one-step, a two-step, an abridged, a skeletal, and four detailed kinetic schemes of hydrogen oxidation have been tested. A new skeletal kinetic scheme of hydrogen oxidation has been developed. The CFD calculations were carried out using ANSYS CFX software. Ignition delay times and speeds of flames were derived from the computational results. The computational data obtained using ANSYS CFX and CHEMKIN, and experimental data were compared. The precision, reliability, and range of validity of the kinetic schemes in CFD simulations were estimated. The impact of kinetic scheme on the results of computations was discussed. The relationship between grid spacing, time step, accuracy, and computational cost was analyzed.

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