Dissertation
Bubble entrainment and transport with application to ship hydrodynamics
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2022
DOI: 10.17077/etd.006420
Abstract
In ship hydrodynamics, bubbly flow is of significant importance as it impacts the wake acoustic and visual signatures, bubble-induced drag reduction, erosion due to cavitation, and other phenomena. Modeling has been and will still be in the foreseeable future the only feasible way of tackling the bubbly flow in ship hydrodynamics. This thesis contributes to three aspects related to the modeling of two-phase flow.
The first contribution is a new method to evaluating the turbulent kinetic energy (TKE) and its dissipation rate with hybrid Reynolds-averaged Navier–Stokes (RANS)/Large eddy simulation (LES) methods. TKE and its dissipation are important inputs to most bubble entrainment and transport models but are not directly obtainable for standard hybrid RANS/LES. A spatial-temporal average method is proposed to extract the mean flow information and a new equation for specific dissipation rate is derived to predict the dissipation rate. Satisfactory agreement with experiments or DNS is demonstrated for decaying/forced homogeneous isotropic turbulence (HIT) and the more complicated flow on a backward-facing step case.
The second contribution is a new bubble breakup model and an improvement to Prince and Blanch (1990) coalescence model. The proposed breakup model uses hybrid energy-force breakup criteria and a full turbulence spectrum. The collision angle effect and efficiency for large turbulent eddies are employed to improve the details of the model. A breakage size distribution function is introduced to account for the probability of each daughter volume fraction after the breakage, improving the model both numerically and physically. A full spectrum model was employed in the coalescence model to be consistent with the breakup model. When tested in two-phase HIT flows, these models predict breakup rate and equilibrium bubble size distributions in line with experimental measurements.
The third contribution consists of improvements to the existing impact and turbulent entrainment models. Geometric information is now modeled into the impact entrainment model to improve its generality. The effect of air cavity and leakage is also included in the model. For the turbulent entrainment model, the single vortex entrainment model is improved using results from direct numerical simulation (DNS) of vortex/free surface interaction and entrainment from Hendrickson et al. (2022), minimizing assumptions and approximations used for this part of modeling. Turbulent vortex circulation and rise speed models from local turbulence model values are developed to integrate the DNS data into the turbulent entrainment model framework of Castro et al. (2016). While the model uses a calibration constant, a unit value provides best results, essentially freeing the model from modeling parameters. A grid convergence study for the full-scale Athena Research Vessel demonstrates that the model is independent of grid resolution for both RANS and DES, and that it is able to predict void fraction and bubble size distribution that match experimental results.
Details
- Title: Subtitle
- Bubble entrainment and transport with application to ship hydrodynamics
- Creators
- Ben Yuan
- Contributors
- Pablo M. Carrica (Advisor)Jiajia Li (Advisor)Christoph Beckermann (Committee Member)Larry J. Weber (Committee Member)H. S. Udaykumar (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Mechanical Engineering
- Date degree season
- Spring 2022
- DOI
- 10.17077/etd.006420
- Publisher
- University of Iowa
- Number of pages
- xii, 146 pages
- Copyright
- Copyright 2022 Ben Yuan
- Language
- English
- Description illustrations
- Illustrations, charts, graphs, tables
- Description bibliographic
- Includes bibliographical references (pages 132-139).
- Public Abstract (ETD)
Bubbles are commonly seen around and in the wake of a sailing ship. These bubbles can affect many engineering aspects of the ship including the drag experienced by the ship and how easily the ship can be detected acoustically or visually. Currently the best method to study bubbly flow is through numerical modeling. This thesis focuses on improving the modeling of entrainment and transport of bubbles, concentrating on three issues of interest for ship hydrodynamics.
The first contribution is bridging the gap between high-resolution turbulence models and the necessary input parameters for bubbly flow models. The goal is to enable use of existing bubble entrainment, breakup, and coalescence models with high-resolution numerical methods, enabling bubbly flow simulations with modern turbulence models.
The second contribution is a new model that handles breakup and coalescence of bubbles. The new breakup model improves over existing models by accounting for more physical processes affecting breakup. The breakup and coalescence models presented herein can operate on wider flow conditions than previous models.
The third contribution is an improved model for predicting the process of air entrainment into water. Geometrical details of the ship are implemented in the model so that it can handle a wide range of ships in complex motions on waves. The model also implements results of recent simulations of air entrainment by a vortex interacting with the water surface, eliminating a source of uncertainty in the previous model.
- Academic Unit
- Mechanical Engineering
- Record Identifier
- 9984271452502771
Metrics
10 File views/ downloads
57 Record Views