Henao-Garcia, Sebastian
(2021)
Investigation of Oscillations in Idealized Katabatic Slope Flows.
Master's Thesis, University of Pittsburgh.
(Unpublished)
Abstract
Katabatic winds are down-slope, drainage flows that are characterized by strong jets of cold air capped by a reverse flow. Katabatic winds typically form when air right above a sloping surface cools rapidly due to radiative heat transfer to clear skies and, subsequently, gets transported down the slope by the action of gravity. Idealized katabatic flows form the theoretical foundation for exploring turbulent winds over complex terrains under stably stratified atmospheric conditions. Recent numerical investigations of idealized katabatic flows have established the presence of organized vortical structures in the laminar flow regime along with an instability map as a function of relevant slope flow dimensionless parameters, including a recently introduced stratification perturbation parameter. The current thesis investigates the oscillatory dynamics of these vortical rolls through direct numerical simulations of idealized katabatic flows for numerous points in the instability map. The simulation results further confirm the presence of both temporal and spatial oscillations in the flow fields that are associated with the emergence and propagation of flow instabilities. Damped en masse oscillations, which were previously identified in the context of turbulent slope flows, are observed to dominate the initial oscillatory stage of laminar katabatic slope flows as well. Unlike in the turbulent regime, these en masse oscillations become insignificant at most heights in the dynamically unstable laminar regime with the emergence of well-defined flow instabilities. Stationary longitudinal rolls, which are dominant at shallow slopes, are observed to meander with increasing stratification perturbation parameter. Traveling slope waves, which emerge on very steep slopes, are observed to be transported by the mean jet velocity of the flow. Both types of instability rolls coexist for certain combinations of the dimensionless parameter space, forming intricate structures that break into turbulence as the flow becomes more dynamically unstable.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
| Creators | Email | Pitt Username | ORCID  |
|---|
| Henao-Garcia, Sebastian | seh159@pitt.edu | seh159 | |
|
| ETD Committee: |
|
| Date: |
3 September 2021 |
| Date Type: |
Publication |
| Defense Date: |
12 July 2021 |
| Approval Date: |
3 September 2021 |
| Submission Date: |
23 July 2021 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Number of Pages: |
104 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Computational Modeling and Simulation |
| Degree: |
MS - Master of Science |
| Thesis Type: |
Master's Thesis |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
katabatic, dynamically unstable, slope flows, stratified atmosphere |
| Date Deposited: |
03 Sep 2021 18:55 |
| Last Modified: |
03 Sep 2021 18:55 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/41480 |
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