Yanni Chang

ORCID Identifier(s)

0000-0002-9999-8274

Graduation Semester and Year

2021

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering

Department

Mechanical and Aerospace Engineering

First Advisor

Albert Y. Tong

Abstract

A series of numerical experiments carried out on the water entry of circular cylinders are presented in this study. A cylinder was entering into the water with a prescribed inclined angle and velocity. The interface between water and air is tracked by the Piecewise Linear Interface Calculation (PLIC) schemes in conjunction with the Volume of Fluid (VOF) method. PLIC schemes have been extensively employed in the VOF method for interface capturing in numerical simulations of multiphase flows. Dynamic overset meshes, which have been widely used for problems with relative motions and complex geometric shapes, are applied to handle the moving cylinder. The numerical model is built on the framework of OpenFOAM which is an open-source C++ toolbox. The results of the numerical model, such as the transient positions and inclined angles of the moving circular cylinder, have been validated with experimental data in the literature. The fluid physics of the oblique water entry problem has been examined. The formation and development of the air entrapment have been explored. Parametric studies on the hydrodynamics of the water entry problem have been performed. It has been revealed that the head geometry, entry impact velocity, entry inclined angle, liquid density, and object density are of considerable significance for the penetration depth and inclination of the diving cylinder. Surface wetness which affects the detachment of the air channel has also been studied. A difficulty of the overset mesh implantation in the PLIC-VOF method is the interpolation of the VOF field. Most of the overset interpolation schemes are designed for continuous flow variables. The acceptor value is evaluated by using a weighted average of the ones of its donors. The weighting factors are obtained by different algebraic methods, such as the averageValue, injection, and inverseDistance schemes. Unlike the continuous flow variables, the VOF field is a step function near the interfaces, which varies from zero to unity rapidly. Thus a specialized overset interpolation scheme is needed for the PLIC-VOF method to transfer the fraction field between the meshes precisely. It should be noted that the inverseDistance scheme has been applied to calculate the weighting factor for the acceptor cell value for the water entry problem. A geometric interpolation scheme of the VOF field in overset meshes for the PLIC-VOF method has also been proposed in this thesis. The VOF value of an acceptor cell is evaluated geometrically with the reconstructed interfaces from the corresponding donor elements. Test cases of advecting liquid columns of different shapes inside a unit square/cube with a prescribed rotational velocity field have been performed to demonstrate the accuracy of the proposed overset interpolation scheme by comparing it with three algebraic ones. The proposed scheme has been shown to yield higher accuracy.

Keywords

Computational fluid dynamics, Multiphase flows

Disciplines

Aerospace Engineering | Engineering | Mechanical Engineering

Comments

Degree granted by The University of Texas at Arlington

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