Three-Dimensional Modeling of Electrostatic Precipitator Using Hybrid Finite Element - Flux Corrected Transport Technique

This thesis presents the results of a three-dimensional simulation of the entire precipitation process inside a single-electrode one-stage electrostatic precipitator (ESP). The model was designed to predict the motion of ions, gas and solid particles. The precipitator consists of two parallel grounded collecting plates with a corona electrode mounted at the center, parallel to the plates and excited with a high dc voltage. The complex mutual interaction between the three coexisting phenomena of electrostatic field, fluid dynamics and the particulate transport, which affect the ESP process, were taken into account in all the simulations. The electrostatic field and ionic space charge density due to corona discharge were computed by numerically solving Poisson and current continuity equations, using a hybrid Finite Element (FEM) - Flux Corrected Transport (FCT) method. The detailed numerical approach and simulation procedure is discussed and applied throughout the thesis. Calculations of the gas flow were carried out by solving the Reynolds-averaged Navier-Stokes equations using the commercial FLUENT 6.2 software, which is based on the Finite Volume Method (FVM). The turbulence effect was included by using the k-ε model included in FLUENT. An additional source term was added to the gas flow equation to include the effect of the electric field, obtained by solving a coupled system of the electric field and charge transport equations, using the User-Defined-Function (UDF) feature of FLUENT. The particle phase was simulated using a Lagrangian-type Discrete Random Walk (DRW) model, where a large number of particles charged by combined field and diffusion charging mechanisms was traced with their motion affected by electrostatic and aerodynamic forces in turbulent flow using the Discrete Phase Model (DPM) and programming UDFs in FLUENT. The airflow patterns under the influence of electrohydrodynamic (EHD) secondary flow and external flows, particle charging and deposition along the channel, and ESP performance in removal of submicron particulates were compared for smooth and spiked discharge electrode configurations in the parallel plate precipitator assuming various particle concentrations at the inlet. Finally, a laboratory scale wire-cylinder ESP to collect conductive submicron diesel particles was modeled. The influence of different inlet gas velocities and excitation voltages on the particle migration velocity and precipitation performance were investigated. In some cases, the simulation results were compared with the existing experimental data published in literature

Fine Scale Simulation of Fractured Reservoirs: Applications and Comparison

Imperial Users onl

Enhancing speed and scalability of the ParFlow simulation code

Regional hydrology studies are often supported by high resolution simulations of subsurface flow that require expensive and extensive computations. Efficient usage of the latest high performance parallel computing systems becomes a necessity. The simulation software ParFlow has been demonstrated to meet this requirement and shown to have excellent solver scalability for up to 16,384 processes. In the present work we show that the code requires further enhancements in order to fully take advantage of current petascale machines. We identify ParFlow's way of parallelization of the computational mesh as a central bottleneck. We propose to reorganize this subsystem using fast mesh partition algorithms provided by the parallel adaptive mesh refinement library p4est. We realize this in a minimally invasive manner by modifying selected parts of the code to reinterpret the existing mesh data structures. We evaluate the scaling performance of the modified version of ParFlow, demonstrating good weak and strong scaling up to 458k cores of the Juqueen supercomputer, and test an example application at large scale.Comment: The final publication is available at link.springer.co

Hydrodynamic Processes in Massive Stars

The hydrodynamic processes operating within stellar interiors are far richer than represented by the best stellar evolution model available. Although it is now widely understood, through astrophysical simulation and relevant terrestrial experiment, that many of the basic assumptions which underlie our treatments of stellar evolution are flawed, we lack a suitable, comprehensive replacement. This is due to a deficiency in our fundamental understanding of the transport and mixing properties of a turbulent, reactive, magnetized plasma; a deficiency in knowledge which stems from the richness and variety of solutions which characterize the inherently non-linear set of governing equations. The exponential increase in availability of computing resources, however, is ushering in a new era of understanding complex hydrodynamic flows; and although this field is still in its formative stages, the sophistication already achieved is leading to a dramatic paradigm shift in how we model astrophysical fluid dynamics. We highlight here some recent results from a series of multi-dimensional stellar interior calculations which are part of a program designed to improve our one-dimensional treatment of massive star evolution and stellar evolution in general.Comment: 10 pages, 4 figures, IAUS 252 Conference Proceeding (Sanya) - "The Art of Modeling Stars in the 21st Century

Multidisciplinary computational aerosciences

As the challenges of single disciplinary computational physics are met, such as computational fluid dynamics, computational structural mechanics, computational propulsion, computational aeroacoustics, computational electromagnetics, etc., scientists have begun investigating the combination of these single disciplines into what is being called multidisciplinary computational aerosciences (MCAS). The combination of several disciplines not only offers simulation realism but also formidable computational challenges. The solution of such problems will require computers orders of magnitude larger than those currently available. Such computer power can only be supplied by massively parallel machines because of the current speed-of-light limitation of conventional serial systems. Even with such machines, MCAS problems will require hundreds of hours for their solution. To efficiently utilize such a machine, research is required in three areas that include parallel architectures, systems software, and applications software. The main emphasis of this paper is the applications software element. Examples that demonstrate application software for multidisciplinary problems currently being solved at NASA Ames Research Center are presented. Pacing items for MCAS are discussed such as solution methodology, physical modeling, computer power, and multidisciplinary validation experiments

Don't Repeat Yourself: Seamless Execution and Analysis of Extensive Network Experiments

This paper presents MACI, the first bespoke framework for the management, the scalable execution, and the interactive analysis of a large number of network experiments. Driven by the desire to avoid repetitive implementation of just a few scripts for the execution and analysis of experiments, MACI emerged as a generic framework for network experiments that significantly increases efficiency and ensures reproducibility. To this end, MACI incorporates and integrates established simulators and analysis tools to foster rapid but systematic network experiments. We found MACI indispensable in all phases of the research and development process of various communication systems, such as i) an extensive DASH video streaming study, ii) the systematic development and improvement of Multipath TCP schedulers, and iii) research on a distributed topology graph pattern matching algorithm. With this work, we make MACI publicly available to the research community to advance efficient and reproducible network experiments