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Item High-fidelity simulations of a rotary bell atomizer with electrohydrodynamic effects(Montana State University - Bozeman, College of Engineering, 2023) Pydakula Narayanan, Venkata Krisshna; Chairperson, Graduate Committee: Mark OwkesAtomizing flows involve the breakup of a liquid into a spray of droplets. These flows play a vital role in various industrial applications such as spray painting and fuel injection. In particular, these processes can have severe impacts especially in automotive paint shops - which can account for up to 50% of the total costs and 80% of the environmental concerns in an automobile manufacturing facility. A device commonly used for painting vehicles is called an electrostatic rotary bell atomizer (ERBA). ERBAs rotate at high speeds while electrically charging the liquid and operating in a background electric field to direct atomized charged droplets towards the target surface. The atomization process directly influences the transfer efficiency (TE) and surface finish quality. Optimal spray parameters used in industry are often obtained from expensive trial-and-error methods. To overcome these limitations, a computational tool has been developed to simulate three-dimensional near-bell ERBA atomization using a high-fidelity volume-of-fluid transport scheme. Additionally, the solver is equipped with physics modules including centrifugal, Coriolis, electrohydrodynamic (EHD), and shear-thinning viscous force models. The primary objective of this research is to investigate the influence of EHD parameters on near-bell atomization of paint and subsequently improve TE in ERBAs in a cost-effective manner. Using the tools developed, numerical simulations are performed to understand the physics of electrically assisted atomization. The influence of various operating parameters, such as liquid flow rate, bell rotation rate, liquid charge density, and bell electric potential, on atomization is examined. Results from a comparative study indicate that the electric field accelerates breakup processes and enhances secondary atomization. The droplet velocity, local Weber number and charge density statistics are also analyzed to understand the complex physics in electrically assisted breakup. Additionally, the effect of shear-thinning behavior of the liquid on atomization is also explored. High-fidelity simulations allow for the extraction of breakup statistics which are otherwise challenging to obtain experimentally. These findings have the potential to drive improvements in the design and operation of ERBAs, leading to enhanced TE and surface finish quality while reducing costs and environmental concerns in automotive paint shops.Item Efficient extraction of atomization processes from high-fidelity simulations(Elsevier BV, 2023-02) Christensen, Brendan; Owkes, MarkUnderstanding the process of primary and secondary atomization in liquid jets is crucial in describing spray distribution and droplet geometry for industrial applications and is essential in the development of physics-based low-fidelity atomization models that can quickly predict these sprays. Significant advances in numerical modeling and computational resources allow research groups to conduct detailed numerical simulations and accurately predict the physics of atomization. These simulations can produce hundreds of terabytes of data. The substantial size of these data sets limits researchers’ ability to analyze them. Consequently, the process of a coherent liquid core breaking into droplets has not been analyzed in simulation results even though a complete description of the jet dynamics exists. The present work applies a droplet physics extraction technique to high-fidelity simulations to track breakup events as they occur and extract data associated with the local flow. The data on the atomization process are stored in a Neo4j graphical database providing an easily accessible format. Results provide a robust, quantitative description of the process of atomization and the details on the local flow field will be useful in the development of low-fidelity atomization models.Item Extraction of droplet genealogies from high-fidelity atomization simulations(Montana State University - Bozeman, College of Engineering, 2019) Rubel, Roland Francis Clark, IV; Chairperson, Graduate Committee: Mark OwkesMany research groups are performing high-fidelity simulations of atomizing jets that are taking advantage of the continually increasing computational resources and advances in numerical methods. These high-fidelity simulations produce extremely large data-sets characterizing the flow and giving the ability to gather a better understanding of atomization. One of the main challenges with these data sets is their large size, which requires developing tools to extract relevant physics from them. The main goal of this project is to create a physics extraction technique to compute the genealogy of atomization. This information will characterize the process of the coherent liquid core breaking into droplets and ligaments which may proceed to break up further. This event information will be combined with detailed information such as droplet size, shape, flow field characteristics, etc. The extracted information will be stored in a database, allowing the information to be readily and quickly queried to assist in the development and testing of low-fidelity atomization models that agree with the physics predicted by high-fidelity simulations.Item Characterization of the primary instability on atomizing jets using dynamic mode decomposition(Montana State University - Bozeman, College of Engineering, 2018) Krolick, William Christopher; Chairperson, Graduate Committee: Mark OwkesNumerical methods have advanced to the point that many groups can perform detailed numerical simulations of atomizing liquid jets and replicate experimental measurements. However, the simulation results have not lead to a substantial advancement to our understanding of these flows due to the massive amount of data produced. In this work, a tool is developed to extract the physics that destabilize the jets liquid core by leveraging dynamic mode decomposition (DMD). DMD takes ideas from the Arnoldi method as well as the Koopman method to evaluate a non-linear system with a low-rank linear operator. The method reduces the order of the simulation results from all the original data through time to a few key pieces of information. Most important of these are the dynamic modes, their time dynamics, and the DMD spectra. In this case, DMD is applied to the jets liquid core outer radius, which is computed at streamwise and azimuthal locations, i.e., R(theta; x). With the DMD data, we obtain the dominant spatial and temporal modes of the system and their characteristics. The dominant modes provide a useful way to collapse the large data set produced by the simulation into a length and timescale that can be used to initiate reduced-order models and numerically categorize the instabilities on the jets liquid core.Item Numerical study of electric Reynolds number on electrohydrodynamic (EHD) assisted atomization(Montana State University - Bozeman, College of Engineering, 2016) Sheehy, Patrick John Harper; Chairperson, Graduate Committee: Mark OwkesIn today's modern world, nearly all industries utilize the benefits of fast, long distance transportation that burning fossil fuels deliver. However, fluctuating fuel prices has created interest in researching alternatives to fossil fuels. Bio-fuels are one of these alternatives, but they generally have a higher viscosity and water content than diesel. This means high pressures are required to atomize the fuel in the combustion chamber, thus bio-fuels are limited to larger or less efficient engines. A potential method to reduce the pressure requirements is to use Electrohydrodynamic (EHD) assisted atomization. EHD assisted atomization injects electrical charges into the liquid fuel before spraying, meaning the fuel has an electrical charge distribution before and after atomization. For many relevant engineering flows, including liquid fuel injection, the charge mobility timescale (time it takes the charges to relax to the fluid-gas boundary) is similar in magnitude to the charge convection timescale (relevant flow time), which leads to a non-trivial electric charge distribution. This distribution within the liquid fuel may enhance atomization, the extent to which is dependent on the ratios of the timescales which are known as the electric Reynolds number (Re subscript e). In this work, a computational approach for simulating two-phase EHD flows is used to investigate the amount Re subscript e influences the resulting atomization quality. The computational approach is second-order, conservative, and is used to consistently transport the phase interface along with the discontinuous electric charge density and momentum. The scheme sharply handles the discontinuous electric charge density, allowing robust and accurate simulations. In addition, this method is modified by a work distribution scheme to improve processor utilization on High Performance Computing (HPC) clusters. Using these methods, multiple three-dimensional test cases are simulated with varying Re subscript e values which highlight the effect of Re subscript e on the atomization efficiency of a liquid jet. Comparison of these cases shows the importance of Re subscript e on atomization and suggests that decreasing Re subscript e (increasing charge mobility) leads to larger concentrations of electric charge density, increased Coulomb force, and ultimately improved break-up during the atomization process.