Geophyscial fluid flows can present different questions and challenges than traditional engineering flows, but share many common features. In the specific case of planetary atmospheres, attempts to realistically simulate these flow numerically is hampered by a lack of data to define what "reality" actually is (with the notable exception of Earth, in which case the problem is arguably too much data). However, humanity is slowly begin to collect an increasing amount of data on atmospheres beyond our own, with recent examples being the Mars missions and the Cassini/Huygens and Galileo probes. This data can be used to both constrain and design atmospheric models, although validation in a traditional engineering sense of the word remains impracticable. To address this, we are attempting to bring together engineering and geophysical fluid dynamics to fill some of the gaps in the available data record.
A collaboration between UK CFD and CPL
The Comparative Planetology Laboratory at the University of Louisville is the home of the Explicit Planetary Isentropic Coordinate General Circulation Model (EPIC GCM), the only established GCM designed to numerically simulate the full variety of planetary atmospheres. UK CFD has teamed up with the CPL to develop a new, flexible planetary boundary layer model to allow improve simulation of terrestrial atmopsheres like those of Venus, Mars, and Titan. A key to this is the adaptation of hybrid turbulence models like Detached Eddy Simulation (DES) into EPIC and validating its performance in engineering benchmark flows that share characteristics of atmospheric ones. An attractive feature of hybrid models is that they can be smoothly shifted into a Large Eddy Simulation (LES) type model in the atmosphere away from the surface, providing a continuous yet practicable turbulence model throughout the atmosphere. To date, variations of the Spalart-Allmaras and Menter SST DES models have been incorporated into EPIC and are being validated with promising results.
Atmosphere Simulation with EPIC
UK CFD is also undertaking an effort to use the EPIC to simulate flows on the outer planets, specifically Neptune and Uranus, in anticipation of future missions beyond Cassini/Huygens at Saturn. Simulations in this direction may serve both to predict the atmospheric conditions of these planets during the mission (which has proven variable in the past) and to provide guidance for possible interaction with the atmosphere by probes through drops or aerocapture. With planetary dynamics occuring on time scales of months and years between data points, this simulation program will require significant computer power, and as such both the cluster design and code optimization aspects of UK CFD play a critical role.
Currently, we have done some work in the EPIC simulations of Neptune , and some work in the EPIC simulations of Uranus . We are considering to include clouds, radiations and convections to these simulations.