Dissertation
Air demand in deep drop structures
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2021
DOI: 10.17077/etd.006017
Abstract
Air entrainment is a complex and often ignored phenomenon in the field of hydraulic engineering. Yet our society relies on many types of air-entraining hydraulic structures to serve the needs of the world’s ever-growing population. As we build larger and more complex hydraulic structures in urban areas, air entrainment issues become ever more critical. In cities, deep vertical drop shafts are commonly used to convey stormwater runoff and sanitary flows hundreds of feet underground into expansive deep tunnel systems, entrapping large amounts of air along with the falling water. Sometimes, entrapped air escapes uncontrollably, manifesting as violent expulsions of air and water at street level. Engineers often utilize hydraulic models to test the performance of deep drop shafts before they are built, but these models imperfectly predict the air-water interactions. However, due to their large size, full-scale evaluations of most hydraulic structures prior to construction are impractical. Therefore, better understanding and development of hydraulic models are vital to building safe and effective structures to serve the needs of current and future generations.
This work investigates air demand in deep drop shafts and the limitations associated with hydraulic modeling of air-water flows. Air demand is simulated using two reduced-scale physical models of vortex-flow drop shafts designed for deep tunnel systems. Air demand is measured for a range of water flow rates, drop shaft heights, drop shaft diameters, and submergence levels, enabling analysis of each parameter with respect to air demand. Dimensional analysis is used to identify the design variables important to air demand and then confirmed through experimental data analysis. Regression analysis is used to fit mathematical expressions to the data and predict air demand from the relevant design variables. Model scale effects are evaluated using three geometrically similar hydraulic models.
The findings show that the primary parameters affecting air demand are water flow rate, drop height, and submergence. Air demand was shown to decrease as water flow rate increases, increase as drop height increases, and decrease as submergence increases. Correction factors were developed to adjust air demands for relative shaft height differences. An empirical relationship to predict air demand was developed from the relevant variables. Correction factors were developed to compensate for model scale effects and adjust model air measurements to full-scale. The data suggests that air flows in deep drop structures are under-represented in reduced-scale models to a larger extent than previously believed.
This dissertation provides new guidance for assessing air demand and understanding the relationships between key design parameters in deep drop shafts. An improved understanding of air-water scale effects expands the effectiveness of reduced-scale hydraulic models in predicting the performance of full-size installations. This work enables several adjustments to model scale air measurements through the use of correction factors. Although this work was motivated by deep drop shafts, the results are relevant to a number of other hydraulic engineering applications associated with air-water flows.
Details
- Title: Subtitle
- Air demand in deep drop structures
- Creators
- Troy Clayton Lyons
- Contributors
- Larry J Weber (Advisor)Gabriele Villarini (Committee Member)Corey Markfort (Committee Member)Allen Bradley (Committee Member)Jacob Odgaard (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Civil and Environmental Engineering
- Date degree season
- Spring 2021
- DOI
- 10.17077/etd.006017
- Publisher
- University of Iowa
- Number of pages
- xxvii, 334 pages
- Copyright
- Copyright 2021 Troy Clayton Lyons
- Comment
- This thesis has been optimized for improved web viewing. If you require the original version, contact the University Archives at the University of Iowa: https://www.lib.uiowa.edu/sc/contact/
- Language
- English
- Description illustrations
- illustrations (some color)
- Description bibliographic
- Includes bibliographical references (page 277-285).
- Public Abstract (ETD)
Deep drop structures entrap significant amounts of air along with falling water, sometimes resulting in violent expulsions of air and water. Presently, numerical and physical models inadequately predict air demand for full-size hydraulic structures. This research simulates air demand using two reduced-scale physical models of vortex-flow drop shafts. Air demand changes due to water flow rate, shaft height, model size, and submergence are evaluated for a wide range of conditions. An empirical relationship is developed to predict air demand in deep drop shafts. Model scale effects are quantified and a correction factor is suggested to adjust model measurements to full-scale. A correction factor for relative shaft height differences is also proposed. The analysis identifies relevant parameters and illustrates how they effect air demand in model and full-size deep drop shafts.
- Academic Unit
- Civil and Environmental Engineering
- Record Identifier
- 9984097478902771
Metrics
101 File views/ downloads
200 Record Views