1,524 research outputs found
An adaptive Cartesian embedded boundary approach for fluid simulations of two- and three-dimensional low temperature plasma filaments in complex geometries
We review a scalable two- and three-dimensional computer code for
low-temperature plasma simulations in multi-material complex geometries. Our
approach is based on embedded boundary (EB) finite volume discretizations of
the minimal fluid-plasma model on adaptive Cartesian grids, extended to also
account for charging of insulating surfaces. We discuss the spatial and
temporal discretization methods, and show that the resulting overall method is
second order convergent, monotone, and conservative (for smooth solutions).
Weak scalability with parallel efficiencies over 70\% are demonstrated up to
8192 cores and more than one billion cells. We then demonstrate the use of
adaptive mesh refinement in multiple two- and three-dimensional simulation
examples at modest cores counts. The examples include two-dimensional
simulations of surface streamers along insulators with surface roughness; fully
three-dimensional simulations of filaments in experimentally realizable
pin-plane geometries, and three-dimensional simulations of positive plasma
discharges in multi-material complex geometries. The largest computational
example uses up to million mesh cells with billions of unknowns on
computing cores. Our use of computer-aided design (CAD) and constructive solid
geometry (CSG) combined with capabilities for parallel computing offers
possibilities for performing three-dimensional transient plasma-fluid
simulations, also in multi-material complex geometries at moderate pressures
and comparatively large scale.Comment: 40 pages, 21 figure
The physics of streamer discharge phenomena
In this review we describe a transient type of gas discharge which is
commonly called a streamer discharge, as well as a few related phenomena in
pulsed discharges. Streamers are propagating ionization fronts with
self-organized field enhancement at their tips that can appear in gases at (or
close to) atmospheric pressure. They are the precursors of other discharges
like sparks and lightning, but they also occur in for example corona reactors
or plasma jets which are used for a variety of plasma chemical purposes. When
enough space is available, streamers can also form at much lower pressures,
like in the case of sprite discharges high up in the atmosphere.
We explain the structure and basic underlying physics of streamer discharges,
and how they scale with gas density. We discuss the chemistry and applications
of streamers, and describe their two main stages in detail: inception and
propagation. We also look at some other topics, like interaction with flow and
heat, related pulsed discharges, and electron runaway and high energy
radiation. Finally, we discuss streamer simulations and diagnostics in quite
some detail.
This review is written with two purposes in mind: First, we describe recent
results on the physics of streamer discharges, with a focus on the work
performed in our groups. We also describe recent developments in diagnostics
and simulations of streamers. Second, we provide background information on the
above-mentioned aspects of streamers. This review can therefore be used as a
tutorial by researchers starting to work in the field of streamer physics.Comment: 89 pages, 29 figure
A new numerical strategy with space-time adaptivity and error control for multi-scale streamer discharge simulations
This paper presents a new resolution strategy for multi-scale streamer
discharge simulations based on a second order time adaptive integration and
space adaptive multiresolution. A classical fluid model is used to describe
plasma discharges, considering drift-diffusion equations and the computation of
electric field. The proposed numerical method provides a time-space accuracy
control of the solution, and thus, an effective accurate resolution independent
of the fastest physical time scale. An important improvement of the
computational efficiency is achieved whenever the required time steps go beyond
standard stability constraints associated with mesh size or source time scales
for the resolution of the drift-diffusion equations, whereas the stability
constraint related to the dielectric relaxation time scale is respected but
with a second order precision. Numerical illustrations show that the strategy
can be efficiently applied to simulate the propagation of highly nonlinear
ionizing waves as streamer discharges, as well as highly multi-scale nanosecond
repetitively pulsed discharges, describing consistently a broad spectrum of
space and time scales as well as different physical scenarios for consecutive
discharge/post-discharge phases, out of reach of standard non-adaptive methods.Comment: Support of Ecole Centrale Paris is gratefully acknowledged for
several month stay of Z. Bonaventura at Laboratory EM2C as visiting
Professor. Authors express special thanks to Christian Tenaud (LIMSI-CNRS)
for providing the basis of the multiresolution kernel of MR CHORUS, code
developed for compressible Navier-Stokes equations (D\'eclaration d'Invention
DI 03760-01). Accepted for publication; Journal of Computational Physics
(2011) 1-2
Implementation of the classical plasma–fluid model for simulation of dielectric barrier discharge (DBD) actuators in OpenFOAM
To simulate the coupled plasma and fluid flow physics of dielectric-barrier discharge, a plasma–fluid
model is utilized in conjunction with a compressible flow solver. The flow solver is responsible for determining the bulk flow kinetics of dominant neutral background species including mole fractions, gas
temperature, pressure and velocity. The plasma solver determines the kinetics and energetics of the
plasma species and accounts for finite rate chemistry. In order to achieve maximum reliability and best
performance, we have utilized state-of-the-art numerical and theoretical approaches for the simulation
of DBD plasma actuators. In this respect, to obtain a stable and accurate solution method, we tested
and compared different existing numerical procedures, including operator-splitting algorithm, super-timestepping, and solution of the Poisson and transport equations in a semi-implicit manner. The implementation of the model is conducted in OpenFOAM. Four numerical test cases are considered in order to
validate the solvers and to investigate the drawbacks/benefits of the solution approaches. The test problems include single DBD actuator driven by positive, negative and sinusoidal voltage waveforms, similar to the ones that could be found in literature. The accuracy of the results strongly depends to the
choice of time step, grid size and discretization scheme. The results indicate that the super-time-stepping
treatment improves the computational efficiency in comparison to explicit schemes. However, the semiimplicit treatment of the Poisson and transport equations showed better performance compared to the
other tested approaches.info:eu-repo/semantics/publishedVersio
Plasma propulsion simulation using particles
This perspective paper deals with an overview of particle-in-cell / Monte
Carlo collision models applied to different plasma-propulsion configurations
and scenarios, from electrostatic (E x B and pulsed arc) devices to
electromagnetic (RF inductive, helicon, electron cyclotron resonance)
thrusters, with an emphasis on plasma plumes and their interaction with the
satellite. The most important elements related to the modeling of plasma-wall
interaction are also presented. Finally, the paper reports new progress in the
particle-in-cell computational methodology, in particular regarding
accelerating computational techniques for multi-dimensional simulations and
plasma chemistry Monte Carlo modules for molecular and alternative propellan
Analysis and development of numerical methodologies for simulation of flow control with dielectric barrier discharge actuators
The aim of this thesis is to investigate and develop different numerical methodologies for
modeling the Dielectric Barrier discharge (DBD) plasma actuators for flow control purposes.
Two different modeling approaches were considered; one based on Plasma-fluid model and
the other based on a phenomenological model.
A three component Plasma fluid model based on the transport equations of charged particles
was implemented in this thesis in OpenFOAM, using several techniques to reduce the
numerical issues. The coupled plasma-fluid problem involves wide range of length and time
scales which make the numerical simulation difficult. Therefore, to obtain stable and
accurate results in a reasonable computational run time, several numerical procedures were
implemented including: semi-implicit treatment of coupling of Poisson equation and charge
density equation, super-time-stepping and operator splitting algorithm.
We examined our code for a constant positive voltage, testing for the dependency of the
behavior of the current density to the selected numerical scheme. In addition, although there
is no clear numerical or experimental benchmark case for DBD plasma actuator problem, the
developed plasma solver was compared quantitively and qualitively with several numerical
works in the literature. Afterward, the developed numerical methodology was used to explore
the possibility of influencing the flow, with higher speed, using nano-second (NS) pulsed DBD
plasma actuator. Therefore, the interaction of the transonic flow and actuation effects of
DBD plasma actuator with nano second pulsed voltage was simulated. The effect of gas
heating and body force was calculated by the plasma solver and was supplied into the gas
dynamic solver for simulating the flow field. Moreover, the results of the plasma fluid model
were used to develop an energy deposition model. It was shown that the energy deposition
model is able to capture the main features of the effect of NS DBD plasma actuators
correctly, with less computational time. It was also shown that fast energy transfer, from
plasma to fluid, leads to the formation of micro-shock waves that modify locally the features
of the transonic flow.
Although the numerical efficiency of the plasma fluid model was improved, the computational
cost of simulating the effect of DBD plasma actuator on a real scale flow situation was still
high. Therefore, a simple model for plasma discharge and its effect on the flow was
developed based on scaling of the thrust generated by DBD plasma actuators. The scaled
thrust model correctly predicts the nonlinear dependency of the thrust produced and the
applied voltage. These scales were then introduced into a simple phenomenological model to
estimate and simulate the body force distribution generated by the plasma actuator.
Although the model includes some experimental correlations, it does not need any fitting
parameter. The model was validated with experimental results and showed better accuracy
compared to previous plasma models.
Using a simple phenomenological model that was developed here, a numerical study was
conducted to investigate and compare the effect of steady and unsteady actuation for controlling the flow at relatively high Reynolds number. Firstly it was shown that the size of
the time-averaged separation bubble is greatly reduced and the flow structure is sensitive to
the frequency of burst modulation of DBD plasma actuators. The results also confirmed that
in the case of unsteady actuation, the burst frequency and burst ratio are crucial parameters
for influencing the capability of the actuators to control the flow. It was found that burst
frequencies near the natural frequencies of the system were able to excite the flow structure
in a resonance mode. This observation also confirmed that with proper frequencies of
excitation, the flow structure can be well rearranged and the flow losses can be reduced.
In the end, Plasma actuators were used for controlling the flow over the Coanda surface of
the ACHEON nozzle. When the plasma actuator was used, it was possible to postpone
separation of the flow and increase the deflection angle of the exit jet of the nozzle. To find
the optimum position of the actuators, seven DBD actuators in forward forcing mode were
placed over the Coanda surface considering the numerically obtained separation points.
Results show that when the actuator is placed slightly before the separation point, enhanced
thrust vectorizing with the use of DBD actuator is achievable. Preliminary results of the
experiments agree with planned/foreseen deflection angle obtained from numerical
computation.O objetivo deste trabalho visa a investigação e desenvolvimento de diferentes métodos
numéricos para modelação de actuadores a plasma de Descarga em Barreira Dieléctrica,
(DBD), tendo em vista o controlo do escoamento na camada limite. Esta modelação numérica
foi abordada de duas formas diferentes, uma baseada num modelo de “plasma-fluid” e outra
fundamentada num modelo fenomenológico.
Neste trabalho é usado um modelo “plasma-fluid” de três componentes que é baseado numa
equação de transporte para as partículas electricamente carregadas. Este foi implementado
no software OpenFOAM fazendo uso de diversas técnicas para minimização de problemas
numéricos que ocorriam na resolução das equações. O cálculo de um problema com
acoplamento entre plasma e fluido envolve uma gama diversa de escalas, tanto temporais
como dimensionais, trata-se então de uma simulação numérica delicada. Como tal, e por
forma a obter resultados estáveis e precisos num tempo de cálculo considerado razoável,
foram implementados diversos procedimentos numéricos, tais como o tratamento semiimplícito
do acoplamento da equação de Poisson com a equação da densidade de carga, o
super-passo-tempo e ainda um algoritmo do tipo divisão de operador.
Foi considerado o caso de uma diferença de potencial positiva, constante, e testada a
dependência da densidade de corrente com os diferentes esquemas numéricos. Apesar de não
existir atualmente uma base de dados, de tipo numérica ou experimental, com casos de teste
para actuadores a plasma tipo DBD, o modelo computacional desenvolvido para calcular o
plasma foi validado qualitativamente, bem como quantitativamente, usando os vários
trabalhos numéricos disponíveis na literatura. Após esta validação inicial, a metodologia
numérica desenvolvida foi utilizada para explorar a possibilidade de influenciar um
escoamento de maior velocidade, através de actuadores a plasma tipo DBD com impulsos de
tensão da ordem de nano-segundos (NS). Desta forma foi simulada a interacção entre um
escoamento transónico e o efeito dos actuadores a plasma tipo DBD sobre o escoamento,
usando pulsos de nano-segundos. O efeito térmico do gás, assim como a força resultante,
foram calculados usando o modelo numérico para cálculo de plasmas desenvolvido neste
trabalho. O resultado obtido é acoplado ao modelo de cálculo para a dinâmica de gases, o
que torna possível simular as condições do escoamento resultante. Adicionalmente, os
resultados do modelo de “plasma-fluid” foram reaproveitados para desenvolver um modelo de
deposição de energia. Este demonstrou ter a capacidade de capturar correctamente as
características principais do efeito de actuadores de plasma, de tipo NS-DBD, com um tempo
de computação menor. Foi demonstrada que uma rápida transferência de energia, do plasma
para o fluido, leva à formação de micro-ondas de choque que alteram localmente as
características do escoamento transónico. Apesar da eficiência numérica do modelo de
“plasma-fluid” ter sido melhorada, o seu custo computacional para a simulação de actuadores
a plasma tipo DBD à escala real continua bastante elevado. Neste sentido, a partir de uma escala de propulsão gerada pelo actuador plasma DBD, foi desenvolvido um modelo mais
simples para a descarga do plasma e para determinar os seus efeitos sobre o escoamento.
O modelo inicial previa correctamente uma dependência não-linear entre a força propulsiva
gerada e a diferença de potencial aplicada. Estas escalas foram então introduzidas num
modelo fenomenológico mais simples para estimar, e simular, a distribuição de forças geradas
pelo actuador a plasma. Apesar de o modelo incluir algumas correlações experimentais, este
não requer qualquer parâmetro de afinação. O modelo foi validado com resultados
experimentais, demonstrando melhores resultados quando comparado com outros modelos de
plasma .
Utilizando um modelo fenomenológico simplificado, que foi desenvolvido no presente
trabalho, foi feito um estudo numérico com o objetivo de investigar, e comparar, os efeitos
que uma actuação estacionária e não-estacionária exibe sobre o controlo do escoamento a
números de Reynolds relativamente elevados. Foi demostrado que a dimensão da bolha de
separação é reduzida em muito e que a estrutura do escoamento é sensível à frequência da
modulação “burst” do actuador a plasma tipo DBD. Os resultados também confirmaram que,
para o caso de actuação não-estacionária, a frequência de “burst” e o “burst ratio”, são
parâmetros cruciais para influenciar a capacidade de controlo do escoamento por parte dos
actuadores a plasma. Determinou-se que as frequências “burst”, semelhantes às frequências
naturais do sistema, são capazes de excitar as estruturas do escoamento num modo de
ressonância. Esta observação confirma igualmente que, com frequências de excitação
apropriadas, a estrutura de um escoamento de camada limite consegue ser correctamente
modificada, e que as perdas no escoamento são reduzidas. Por fim, os actuadores a plasma
foram utilizados para o controlo do escoamento sobre uma superfície Coanda de uma tubeira.
Quando nesta foi aplicado um plasma, tornou-se possível retardar a separação do escoamento
e aumentar o ângulo de deflexão do jacto gerado pelo propulsor. Por forma a encontrar a
posição óptima para os actuadores, sete actuadores de tipo DBD foram distribuídos ao longo
da superfície Coanda, tendo em consideração os pontos de separação do escoamento na
camada limite obtidos numericamente. Os resultados mostram que quando o actuador DBD é
colocado ligeiramente antes do ponto de separação do escoamento, há um aumento da
capacidade de controlo e vectorização do jacto gerado. Os resultados preliminares das
experiências efectuadas estão de acordo com o ângulo de deflexão do jacto previsto pelo
modelo computacional
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