Air entrainment and micro-bubble generation by turbulent breaking waves
Abstract/Contents
- Abstract
- Bubble generation and air entrainment on ocean surfaces and behind ships are complex phenomena which usually accompany turbulent flows. Non-linear wave-breaking events entrain air and generate turbulence. Turbulence consequently fragments the entrained air into smaller bubbles. This process drastically increases the flux of air into the oceans and rivers, which is important for both aerating the water bodies and reducing greenhouse gases from the atmosphere. Wave breaking and bubble generation behind ships also have important effects on the hydrodynamics of ships and on their performance. The bubbly flow as a result of ship passage generates ship trails which remain for several minutes thereafter. Although turbulence is responsible for the fragmentation of larger bubbles into smaller ones, it cannot be the cause of the generation of micron-size bubbles. These bubbles are observed in ship wakes and natural waves and are associated with liquid-liquid impact events. These phenomena, due to their complexity, are far from being completely understood. In addition, there is missing quantitative connection between the large-scale non-linear wave-breaking events and the micron-size bubble generation as a result of impact events. There is a large-scale separation between these two phenomena which makes elucidation of the problem very challenging. The aim of this study is to use direct numerical simulations of turbulent hydraulic jumps as canonical representation of non-linear breaking waves, to study the air entrainment and large bubble generation. Furthermore, this study provides statistics of liquid-liquid impact events, which are precursors to micro-bubble generation in these flows. As far as we know, the present work is the first direct numerical simulation of turbulent hydraulic jumps, as well as the first attempt to obtain interface impact statistics in a stationary turbulent breaking wave. In addition to bubble generation, we investigate turbulence statistics such as mean and turbulent velocity fluctuations, Reynolds stress tensors, turbulence production terms, energy spectra and one-dimensional energy budget of the flow. Finally, we present investigation of the effect of relevant non-dimensional parameters such as Weber number and Reynolds number on both large bubbles and impact statistics in these flows.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2016 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Mortazavi, Milad |
|---|---|
| Associated with | Stanford University, Department of Mechanical Engineering. |
| Primary advisor | Mani, Ali, (Professor of mechanical engineering) |
| Thesis advisor | Mani, Ali, (Professor of mechanical engineering) |
| Thesis advisor | Eaton, John K |
| Thesis advisor | Moin, Parviz |
| Advisor | Eaton, John K |
| Advisor | Moin, Parviz |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Milad Mortazavi. |
|---|---|
| Note | Submitted to the Department of Mechanical Engineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2016. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2016 by Seyed Milad Mortazavi Ravari
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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