Gotowa bibliografia na temat „Electrostatic turbulence”

The performance of Electrostatic Precipitator (ESP) is significantly affected by complex flow distribution. Recent years, many numerical models have been developed to model the particle motion in the electrostatic precipitators. The computational fluid dynamics (CFD) code FLUENT is used in description of the turbulent gas flow and the particle motion under electrostatic forces. The gas flow are carried out by solving the Reynolds-averaged Navier-Stokes equations and turbulence is modeled by the k-ε turbulence model. The effect of electric field is described by a series equations, such as the electric field and charge transport equations, the charged particle equation, the charge conservation equation, the mass and momentum equations of gas, the mass and momentum equations of particle and so on. The particle phase is simulated by using Discrete Phase Model (DPM). The simulations showed that the particle trajectory inside the ESP is influenced by both the aerodynamic and electrostatic forces. The simulated results have been validated by the established data.

AbstractThe influence of an ergodic magnetic limiter (EML) on plasma turbulence is investigated in the Tokamak Chauffage Alfvén Brésilien (TCABR), a tokamak with a peculiar natural superposition of the electrostatic and magnetic fluctuation power spectra. Experimental results show that the EML perturbation can reduce both the magnetic oscillation and the electrostatic plasma turbulence. Whenever this occurs, the turbulence-driven particle transport is also reduced. Moreover, a bispectral analysis shows that the nonlinear coupling between low- and high-frequency electrostatic fluctuations increases significantly with the EML application.

The magnetic drift and the electric potential play an important role in microtearing destabilization by increasing the growth rate of this instability in the presence of collisions, while in electrostatic plasma micro-turbulence, zonal electric potentials can have a strong impact on turbulent saturation. A reduced model has been developed, showing that the Rechester–Rosenbluth model is a good model for the prediction of electron heat diffusivity by microtearing turbulence. Here, nonlinear gyrokinetic flux-tube simulations are performed in order to compute the characteristics of microtearing turbulence and the associated heat fluxes in tokamak plasmas and to assess how zonal flows and zonal fields affect saturation. This is consistent with a change in saturation mechanism from temperature corrugations to zonal field- and zonal flow-based energy transfer. It is found that removing the electrostatic potential causes a flux increase, while linearly stabilization is observed.

Abstract. The electron component of intensive electric currents flowing along the geomagnetic field lines excites turbulence in the thermal magnetospheric plasma. The protons are then scattered by the excited electromagnetic waves, and as a result the plasma is stable. As the electron and ion temperatures of the background plasma are approximately equal each other, here electrostatic ion-cyclotron (EIC) turbulence is considered. In the nonisothermal plasma the ion-acoustic turbulence may occur additionally. The anomalous resistivity of the plasma causes large-scale differences of the electrostatic potential along the magnetic field lines. The presence of these differences provides heating and acceleration of the thermal and energetic auroral plasma. The investigation of the energy and momentum balance of the plasma and waves in the turbulent region is performed numerically, taking the magnetospheric convection and thermal conductivity of the plasma into account. As shown for the quasi-steady state, EIC turbulence may provide differences of the electric potential of ΔV≈1–10 kV at altitudes of 500 < h < 10 000 km above the Earth's surface. In the turbulent region, the temperatures of the electrons and protons increase only a few times in comparison with the background values.Key words. Magnetospheric physics (electric fields; plasma waves and instabilities)

The prediction of particle and scalar transport in a complex geometry with turbulent flow driven by fans is considered. The effects of using different turbulence models, anisotropy, flow unsteadiness, fan swirl, and electrostatic forces on particle trajectories are shown. The turbulence models explored include k−l, zonal k−ε/k−l, and nonlinear eddy viscosity models. Particle transport is predicted using a stochastic technique. A simple algorithm to compute electrostatic image forces acting on particles, in complex geometries, is presented. Validation cases for the particle transport and fluid flow model are shown. Comparison is made with new smoke flow visualization data and particle deposition data. Turbulence anisotropy, fan swirl, and flow unsteadiness are shown to significantly affect particle paths as does the choice of isotropic turbulence model. For lighter particles, electrostatic forces are found to have less effect. Results suggest, centrifugal forces, arising from regions of strong streamline curvature, play a key particle deposition role. They also indicate that weaknesses in conventional eddy viscosity based turbulence models make the accurate prediction of complex geometry particle deposition a difficult task. Axial fans are found in many fluid systems. The sensitivity of results to their modeling suggests caution should be used when making predictions involving fans and that more numerical characterization studies for them could be carried out (especially when considering particle deposition). Overall, the work suggests that, for many complex-engineering systems, at best (without excessive model calibration time), only qualitative particle deposition information can be gained from numerical predictions.

A numerical MHD model is developed to investigate acceleration and heating of both thermal and auroral plasma. This is done for magnetospheric flux tubes in which intensive field aligned currents flow. To give each of these tubes, the empirical Tsyganenko model of the magnetospheric field is used. The parameters of the background plasma outside the flux tube as well as the strength of the electric field of magnetospheric convection are given. Performing the numerical calculations, the distributions of the plasma densities, velocities, temperatures, parallel electric field and current, and of the coefficients of thermal conductivity are obtained in a self-consistent way. It is found that EIC turbulence develops effectively in the thermal plasma. The parallel electric field develops under the action of the anomalous resistivity. This electric field accelerates both the thermal and the auroral plasma. The thermal turbulent plasma is also subjected to an intensive heating. The increase of the plasma of the Earth's ionosphere. Besides, studying the growth and dispersion properties of oblique ion cyclotron waves excited in a drifting magnetized plasma, it is shown that under non-stationary conditions such waves may reveal the properties of bursts of polarized transverse electromagnetic waves at frequencies near the patron gyrofrequency.

The increasing demand for new energy production has become the constant leitmotif of the society we live in. The impossibility of meeting such request in an economically feasible and environmentally friendly manner within the existing portfolio of options is now a global self-awareness. The International Energy Agency has been thoroughly documenting through its reports during the last years that the known reserves of natural gas and oil will be exhausted in decades, due to overpopulation and increasing energy demand. Consequently, a crucial issue will soon concern supply problems. This is where the research on fusion as energy source enters the picture. In order to demonstrate the feasibility of fusion as an energy source, the international scientific community has devoted countless efforts to the research on controlled thermonuclear fusion. The main and biggest experiment under construction, ITER, is the result of the cooperation among many countries throughout the world and it will be a test bench for fusion physics and fusion engineering. Among the different magnetic configurations suitable for fusion devices, the reversed-field pinch has demonstrated to be an excellent tool for plasma physics studies, although it is not accounted as a viable device for commercial energy production. The RFX-mod experiment hosted by Consorzio RFX in Padova is the biggest RFP device in the world. The research activity that will be presented in this thesis has been developed mainly at RFX-mod in Padova but has also involved the participation to an experimental campaign on the COMPASS tokamak in Prague. The research activity that will be presented in this thesis focuses on the characterization of 3D effects on transport mechanisms at the edge region of fusion plasmas in RFX-mod. The device is highly versatile: it can be operated both in reversed-field pinch and in tokamak magnetic configuration. A detailed description of transport properties at the plasma edge in both configurations will be given in the development of the thesis. The approach that will be followed can be described in terms of a twofold itinerary shared between the investigation of electrostatic fluctuations of transport properties through insertable probes and the study of magnetic topology modifications due to spontaneous 3D processes. The thesis is organized as follows: Part I, Introduction. In the first part of the thesis, all the background information needed for the development of the work will be introduced. In chapter 1 the concept of plasma and fusion physics will be discussed together with a detailed description of the two magnetic configurations for fusion devices relevant for analyses: reversed-field pinch (RFP) and tokamak. In chapter 2 the RFP dynamics will be described in details by introducing Taylor relaxation theory and the two main topologies also experimentally observed: the Single Helicity (SH) and the Multiple Helicity (MH) states. Then, RFX-mod edge region will be specifically described and the main tools used in the analyses will be introduced. The chapter will close with the introduction of a comparison between RFP and tokamak’s edge region through the analogy of a common 3D structure when external magnetic perturbations are applied. Part II, Transport analysis. In chapter 3 the two experimental configurations in which RFX-mod operates will be presented. The insertable U-probe used in the experiments will be described together with the theory upon which the collection of measurements relies. The investigation of electrostatic fluctuations of transport properties at the edge will be discussed. Studies on transport mechanism around different topological regions in presence of an externally applied magnetic perturbation will be shown for both reversed-field pinch and tokamak configuration in the RFX-mod device. Part III, Topology analysis. The study of magnetic topology modifications develops through analyses of spontaneous magnetic reconnection events in reversed-field pinch magnetic configuration. In chapter 4 reconnection models will be briefly discussed. Then, crash events in RFX-mod will be presented and the adopted analysis technique will be thoroughly explored. In the second part of the chapter the ion energy analyzer will be described together with its application in measurements of ion temperature profile in COMPASS tokamakand in RFX-mod. Part IV, Conclusions. In chapter 5 the results of the thesis are collected and discussed. In conclusion, a section entitled Summary and future perspectives is added where the main results are tautly summarized in view of future perspectives of research. Part V, Appendixes. In Appendix A a detailed description of MagnetoHydroDynamics framework for plasma physics is given. In Appendix B transport equations will be treated in details.
Il crescente aumento nella richiesta di produzione energetica è diventato un costante leitmotif che caratterizza la società in cui viviamo. L'impossibilità di riuscire a soddisfare tali richieste sfruttando opzioni già esistenti che siano economicamente vantaggiose ed al contempo rispettino l’ambiente, è ormai una consapevolezza globalmente diffusa. La International Energy Agency ha esaustivamente documentato attraverso i suoi report annuali che le riserve di gas naturale e combustibile fossile si esauriranno nel giro di qualche decade a causa della sempre più crescente richiesta di energia. Come provvedere a soddisfare le esigenze energetiche di una popolazione mondiale in continuo aumento diventerà ben presto un problema critico. E' all'interno di questo quadro globale che entra in gioco la ricerca sulla fusione come risorsa energetica. Al fine di poter dimostrare la sfruttabilità della fusione nucleare quale risorsa energetica, la comunità scientifica internazionale ha da anni continuato ad investire nella ricerca sulla fusione termonucleare controllata. Ad oggi è nelle fasi finali di costruzione il più grande esperimento che coinvolga trasversalmente ricercatori da ogni parte del mondo. L'esperimento è denominato ITER (International Thermonuclear Experimental Reactor) e rappresenterà un banco di prova per la fisica della fusione e l’ingegneria. Tra le possibili configurazioni magnetiche adottabili sperimentalmente in una macchina da fusione, quella a campo magnetico rovesciato si è rivelata essere un eccellente strumento per studiare la fisica del plasma e le innumerevoli sfide scientifiche che essa pone. Tuttavia, per svariati motivi non è previsto l'utilizzo di tale configurazione in un reattore a fusione che produca energia a fini commerciali. L'esperimento RFX-mod ospitato presso il Consorzio RFX a Padova è il reversed-field pinch (RFP) più grande al mondo. L'attività di ricerca che verrà presentata in questo lavoro di tesi è stata svolta principalmente a Padova su RFX-mod ma ha anche previsto e contemplato la partecipazione ad una campagna sperimentale sul tokamak COMPASS a Praga. L’attività di ricerca che verrà presentata in questa tesi si concentra sulla caratterizzazione degli effetti 3D sui meccanismi di trasporto nella regione più esterna del plasma di RFX-mod. La macchina risulta essere estremamente versatile in quanto sono possibili operazioni in configurazione a campo rovesciato e in configurazione tokamak. Nello svolgimento della tesi verrà fornita una descrizione dettagliata delle proprietà di trasporto al bordo del plasma in entrambe le configurazioni magnetiche. L'approccio che verrà seguito può essere descritto in termini di un duplice percorso condiviso tra l'investigazione delle fluttuazioni elettrostatiche delle proprietà di trasporto effettuato attraverso l'utilizzo di sonde inseribili nel plasma e lo studio dei cambiamenti della topologia magnetica dovuti a meccanismi spontanei di tipo 3D. La tesi viene così organizzata: Parte I, Introduzione. Nella prima parte della tesi verranno introdotte tutte le nozioni di base utili allo svolgimento del lavoro. Nel capitolo 1 sarà discusso il concetto di plasma e fisica della fusione assieme ad una descrizione dettagliata delle due configurazioni magnetiche rilevanti ai fini delle analisi effettuate: la configurazione reversed-field pinch (RFP) e tokamak. Nel capitolo 2 la dinamica di un RFP verrà dettagliatamente descritta attraverso la teoria di Taylor. Inoltre verranno discussi gli stati a singola e multipla elicità (stati SH e MH), caratteristici della dinamica di un RFP. Successivamente verrà descritta la regione più esterna del plasma di RFX-mod, anche attraverso gli strumenti principali utilizzati nelle analisi effettuate. Il capitolo si concluderà quindi con l'introduzione di una analogia, che sarà dominante in tutto il corpo della tesi, tra la regione esterna di un plasma di tipo RFP e di uno di tipo tokamak durante esperimenti che prevedano l'applicazione di perturbazioni magnetiche. Parte II, Analisi di trasporto. Il capitolo 3 si apre con la presentazione delle due configurazioni sperimentali adottate per RFX-mod ai fini delle analisi di trasporto. Negli esperimenti è stata utilizzata la sonda inseribile U-probe, che verrà descritta successivamente assieme alla teoria su cui si basano le misure da essa raccolte. Verranno quindi discussi i risultati derivanti dall'investigazione delle fluttuazioni elettrostatiche nella regione di bordo del plasma. Verranno di seguito presentati gli studi sui meccanismi di trasporto in differenti regioni topologiche in presenza di una perturbazione magnetica esternamente applicata. Tali risultati verranno mostrati per esperimenti condotti su RFX-mod sia in configurazione reversed-field pinch che in configurazione tokamak. Parte III, Analisi topologiche. Lo studio dei cambiamenti della topologia magnetica si sviluppa attraverso l'analisi di eventi spontanei di riconnessione magnetica in configurazione a campo rovesciato. Nel capitolo 4 verranno inizialmente discussi alcuni modelli di riconnessione magnetica. Verranno quindi presentati i cosiddetti eventi di crash all'interno di RFX-mod e verrà dettagliatamente descritta la tecnica di analisi adottata. Nella seconda parte del capitolo verranno descritti gli esperimenti effettuati sul tokamak COMPASS e su RFX-mod sfruttando un'altra sonda inseribile che ha lo scopo di analizzare il profilo di temperatura ionica. Parte IV, Conclusioni. Nel capitolo 5 sono raccolti e discussi i risultati della tesi. Infine, viene fornita una sezione in cui i principali risultati sono trattati sinteticamente insieme ai problemi rimasti aperti in vista di future prospettive di ricerca. Parte V, Appendici. In Appendice A è possibile trovare una descrizione dettagliata del formalismo della Magnetoidrodinamica mentre in Appendice B vengono trattate in dettaglio le equazioni per il trasporto utili ai fini della tesi.

Neste trabalho foi realizado um estudo experimental da turbulência e do transporte de partículas e energia induzido por flutuações na borda do plasma do tokamak TBR-1. Para isto, foi utilizado um conjunto de sondas eletrostáticas (incluindo uma sonda tripla de resposta rápida) e magnéticas, especialmente construído para este fim. Técnicas de análise espectral foram aplicadas aos dados e permitiram verificar a influência das flutuações da temperatura nos parâmetros de transporte. Os resultados mostram que o nível relativo das flutuações da temperatura é da ordem de 10% e os da densidade e do potencial variam de ~10 a ~ 30 %. As flutuações eletrostáticas possuem faixas largas de freqüência e números de onda, o que caracteriza a borda do plasma como um meio turbulento. Estas flutuações se propagam no sentido da deriva diamagnética dos íons. A correção das flutuações das grandezas do plasma utilizando as flutuações da temperatura causou mudanças significativas nos transportes de partículas e energia induzidos por flutuações, nas posições mais internas da borda do plasma. O tempo de confinamento de partículas, calculado a partir deste transporte, está na faixa de ~1 a ~ 1,5 ms, que é da mesma ordem do tempo de confinamento obtido por outros métodos, indicando assim que o transporte induzido por flutuações pode ser considerado como o principal processo de perda de partículas na borda do plasma. Utilizando perturbações magnéticas externas, verificamos que a temperatura e a densidade diminuem e há alterações significativas nas características das flutuações eletrostáticas e magnéticas. Os transportes de partículas e de energia também são afetados, diminuindo nas posições mais internas da borda do plasma. Estes efeitos mostram que a borda do plasma torna-se um meio menos turbulento e que estas perturbações são um meio efetivo de controle do transporte nesta região.
In this work we report an experimental study of the turbulence and the particle and energy transport due to fluctuations in the plasma edge of the TBR-1 tokamak. For this study a special set of electrostatic probes (including one fast response triple probe) and magnetic probes have been constructed. The triple probe permitted measurements of temperature fluctuations. Spectral analysis techniques were applied to the data and permitted to verify the influence of temperature fluctuations on the transport parameters. Our results indicate that the relative level of temperature fluctuations is ~ 10 % and the relative levels of density and potential fluctuations are in the range from ~ 10 to ~ 30 %. The electrostatic fluctuations are broadband in frequencies and wave numbers indicating that plasma edge is a turbulent medium. These fluctuations propagate in the ion diamagnetic drift direction. If temperature fluctuations are taken into account, significant modifications in the calculated transport parameters are obtained mainly in the inner positions of plasma edge. The particle confinement time, calculated from the transport corrected by the temperature fluctuations, is in the range from ~ 1 to ~ 1.5 ms. These values are comparable with those calculated by using other methods, indicating that transport induced by fluctuations is the main process of particle loss in the TBR-1 plasma edge. Controlled electrical currents circulating in helical windings were used to produce magnetic perturbations. These perturbations produce a decrease in the plasma mean density and temperature, and a significant alteration in the electrostatic and magnetic fluctuations. The transport parameters are also affected, decreasing at the inner positions of the plasma edge. The effect of these magnetic fields shows that these perturbations are an effective mean to control the transport in this region.

In gas-solid fluidized beds, the generation of electrostatic charges due to continuous contacts between fluidizing particles, and the particles and the fluidization vessel wall, is unavoidable. Industrial operations, such as the production of polyethylene, are susceptible to significant operational challenges caused by electrostatics including reactor wall fouling, a problem known as “sheeting”. The formation of particle sheets can require shutdown periods for clean-up which results in significant economic losses. To gain a better understanding of the underlying mechanisms of electrostatic charging in gas-solid fluidized beds, in an attempt to eliminate or minimize this problem, a pilot-scale pressurized gas-solid fluidization system was designed and built, housing an online electrostatic charge measurement technique consisting of two Faraday cups. The system permits the study of the degree of particle wall fouling at pressures and temperatures up to 2600 kPa and 100°C, respectively, and gas velocities up to 1 m/s (covering a range including turbulent flow regime). The system also allowed, for the first time, the measurement of the fluidizing particles’ mass, net charge and size distribution in various regions of the bed, especially those related to the wall coating under the industrially relevant operating conditions of high pressures and gas velocities. Experimental trials were carried out using polyethylene resin received from commercial reactors to investigate the influence of pressure and gas velocity on the bed hydrodynamics and in turn, the degree of bed electrification. Mechanisms for particle charging, migration and adherence to the column wall were proposed. The size distribution of the gas bubbles shifted towards smaller bubbles as the operating pressure was raised. Thus, higher pressures lead to greater mixing within the bulk of the bed and resulted in a higher degree of particle wall fouling. Moreover, the extent of wall fouling increased linearly with the increase in gas velocity and as the bed transitioned to turbulent regime, due to the increase in particle-wall contacts. Bipolar charging was observed especially within the wall coating with smaller particles being negatively charged. Overall, particle-wall contacts generated negatively charged particles resulting in a net negative charge in the bed, whereas particle-particle contacts generated positively and negatively charged particles resulting in no net charge when entrainment was negligible. The formation of the wall layer and its extent was influenced by the gravitational and drag forces balancing the image force and Coulomb forces (created by the net charge of the bed and the metallic column wall as the attraction between oppositely charged particles).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1992.
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Rolling detachment of micro particles in the presence of electrostatic and capillary forces based on the maximum adhesion resistance was studied. The effective thermodynamic work of adhesion including the effects of electrostatic and capillary forces was used in the analysis. The JKR and DMT models for elastic interface deformations and the Maugis-Pollock model for the plastic deformation were extended to include the effect of electrostatic and capillary forces. Under turbulent flow conditions, the turbulence burst model was used to evaluate the airflow velocity near the substrate. The critical shear velocities for removal of particles of different sizes were evaluated and the results were compared with those without electrostatic and capillary forces. It shows that the capillary forces significantly increases the critical shear velocities for particles of all sizes, while the electrostatic forces only have major effects on large particles. The model predictions were compared with the available experimental data and good agreement was observed.

Rolling detachment of micro particles in turbulent flows under the presence of electrostatic and capillary forces was studied. The maximum adhesion resistance model and the effective thermodynamic work of adhesion including the effects of electrostatic and capillary forces were used in the analysis. The JKR and DMT models for elastic interface deformations and the Maugis-Pollock model for the plastic deformation were extended to include the effect of electrostatic and capillary forces. The turbulence burst model was used to evaluate the airflow velocity near the substrate. The critical shear velocities for removal of particles of different sizes were evaluated and the results were compared with those without electrostatic and capillary forces. The relative critical shear velocities as well as the material dependence were also studied. The effect of the direction of the combined Coulomb force was also included. The predictions of the electric detachment fields for particles were compared with the available experimental data and good agreement was observed.

The design, fabrication, and characterization of a surface micromachined, front-vented, 64 channel (8×8), capacitively sensed pressure sensor array is described. The array was fabricated using the MEMSCAP PolyMUMPs® process, a three layer polysilicon surface micromachining process. An acoustic lumped element circuit model was used to design the system. The results of our computations for the design, including mechanical components, environmental loading, fluid damping, and other acoustic elements are detailed. Theory predicts single element sensitivity of 1 mV/Pa at the gain stage output in the 400–40,000 Hz band. A laser Doppler velocimetry (LDV) system has been used to map the spatial motion of the elements in response to electrostatic excitation. A strong resonance appears at 480 kHz for electrostatic excitation, in good agreement with mathematical models. Static stiffness measured electrostatically using an interferometer is 0.1 nm/V2, similar to the expected stiffness. Preliminary acoustic sensitivity studies show single element acoustic sensitivity (as a function of frequency) increasing from 0.01 mV/Pa at 200 Hz to 0.16 mV/Pa at 2 kHz. A more in depth analysis of acoustic sensitivity is ongoing.

An integrated numerical simulation tool that couples the Reynolds averaged Navier-Stokes (RANS) or the large eddy simulation (LES) solver for incompressible flows with the dielectric barrier discharge (DBD) electro-hydrodynamic (EHD) body force model has been developed. The EHD body force model is based on solving the electrostatic equations for the electric potential due to applied voltage and the net charge density due to ionized air. The boundary condition for the charge density on the dielectric surface is obtained from a Space-Time Lumped-Element (STLE) circuit model that accounts for the time and space dependence of air ionization on the input voltage amplitude, frequency, electrode geometry, and dielectric properties. The development of the numerical simulation tool is based on the framework of NavyFOAM using a multi-domain approach. The electric potential equation, the net charge density equation, and the flow equations are solved in separate computational domains. All equations are discretized in space using the cell-centered finite volume method. Parallel computation is implemented using domain-decomposition and message passing interface (MPI). Due to a large disparity in time scales between the electric discharge and the flow, a multiple sub-cycle technique is used in coupling the plasma solver and the flow solver. This paper focuses on its application to numerical simulation of flow separation and control over a high-lift flapped airfoil at a Reynolds number of 240,000. The 2-D unsteady RANS simulation utilized the Wilcox k-ω, the SST k-ω, and the k-kl-ω turbulence models. For the baseline case, in comparison with the measurement, the k-kl-ω model captures the feature of the unsteadiness of flow field associated with flow separation and shedding of vortices, better than the Wilcox k-ω and SST k-ω models. In the RANS simulations for flow separation control with DBD plasma actuation, the actuator is driven by voltage signals of a continuous or an amplitude-modulated sine waveform with a range of voltage amplitudes. The numerical results indicate that the modulated forcing is more effective than the continuous forcing for a certain range of applied voltages. The electrical power consumption calculated by the plasma model fits to a parabolic curve as a function of the root-mean-square of applied voltage.