Geometric volume-of-fluid framework for simulating two-phase flows on unstructured meshes
- Two-phase flows appear frequently in nature and industry. An important example, which impacts the efficiency of combustion engines, is the atomization of an injected liquid jet into an evaporable spray. Accurately simulating two-phase flows in complex engineering applications poses several challenges for numerical modeling. Material properties are discontinuous and can vary greatly between the two phases; for example, the density ratio of air-water flows in atmospheric conditions is approximately 1:1000. The curvature of the phase interface generates a singular surface tension force, which is only active at the interface. The curvature is a higher-order term that requires second derivatives of the interface position, which are susceptible to numerical error amplification. The accurate tracking of the phases in applications that generate a breadth of interfacial length scales, such as breaking waves and jet atomization, require schemes that prevent the dissipation of the small-scale features. Discretizations on unstructured grids are necessary to simulate two-phase flows that include complex engineering devices, such as fuel injectors in a diesel combustor. The present work addresses these challenges using a geometric volume-of-fluid framework. In the present volume-of-fluid method, the interface evolution is implicitly tracked using the fraction of the liquid volume within each cell. The interface is represented by a series of discontinuous planes, reconstructed by the local liquid volume fraction. As such, the approach naturally handles large changes in the interfacial topology. The piecewise-planar representation of the interface, combined with tools from computational geometry, facilitates exact numerical integration over the phases on unstructured meshes. The focus of this dissertation is to discuss the novel developments of the unstructured two-phase flow solver: an accurate and convergent approach for calculating the interface normals and curvatures, a discretely conservative and bounded volume-of-fluid advection method, a two-phase fractional-step method that can handle singular surface tension forces and large density ratios, and a non-convex polyhedral library to perform the geometric operations required by the developments. The novel components of the framework are assessed using canonical static, kinematic and dynamic test cases on various unstructured meshes to demonstrate its cost, robustness and accuracy. Finally, the relevance of the method to engineering applications is established through a simulation of the atomization of a diesel fuel from a Bosch injector.
|Type of resource
|electronic; electronic resource; remote
|1 online resource.
|Ivey, Christopher Blake
|Stanford University, Department of Mechanical Engineering.
|Statement of responsibility
|Christopher Blake Ivey.
|Submitted to the Department of Mechanical Engineering.
|Thesis (Ph.D.)--Stanford University, 2017.
- © 2017 by Christopher Blake Ivey
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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