Year of Publication

2009

Degree Name

Doctor of Philosophy (PhD)

Document Type

Dissertation

College

Engineering

Department

Mechanical Engineering

First Advisor

Dr. Raymond P. LeBeau

Second Advisor

Dr. Vincent R. Capece

Abstract

Computational Fluid Dynamics (CFD) has been applied to many areas. As one of the most important fluids, the atmosphere is closely related to people’s life. Studying the atmospheres on other planets can help people understand the Earth’s atmosphere and the climate and weather phenomena in it. Because of the complexity of a planetary atmosphere and the limitation of observations, applying CFD to the study of planetary atmospheres is becoming more and more popular. This kind of CFD simulations will also help people design the mission to the extra planets.

In this dissertation, through CFD simulations, we studied the three important phenomena in a planetary atmosphere: vortices, zonal winds and clouds. The CFD model Explicit Planetary Isentropic Coordinate (EPIC) Global Circulation Model (GCM) was applied in these simulations. Dynamic simulations of the Great Dark Spots (GDS) on Neptune and the Uranian Dark Spot (UDS) were performed. In this work, constructed zonal wind profiles and vertical pressure-temperature profile were constructed based on the observational data. Then, we imported a two-flux radiation model with two-band absorption coefficients into EPIC to study the seasonal changes on Uranus. Finally, a methane cloud model was imported to study the cloud formation around a great vortex and its effects on the vortex.

In the process of the dynamic simulations of Neptune’s atmosphere and its vortices in it, the parameters about the background and the vortex itself were investigated to try to fit the observational results. We found that a small gradient of background absolute vorticity near a GDS is needed to sustain a great vortex in the atmosphere. The drift rate and oscillations of a GDS are closely related to the zonal wind profile and the vortex characteristics. The dynamic simulations of the UDS suggested why it is hard to observe a great vortex on Uranus and indicated that a region of near constant absolute vorticity appearing at ∼28◦N in the zonal wind profile is possibly recommended to the sustainability of the UDS.With the two-flux radiation model, we simulated the seasonal change of the zonal wind profile on Uranus. The observational temperature distribution and global convection were also achieved. With the methane cloud model, we simulated the poleward cloud above great vortices on both Neptune and Uranus. The results suggested that the cloud model can help the GDS on Neptune to keep its shape and moderate its oscillations. Similarly, it can also help the UDS to keep its form.

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