Date of Award


Document Type


Degree Name

Master of Science


Department of Aeronautics and Astronautics

First Advisor

Andrew J. Lofthouse, PhD.


In the world of computational fluid dynamics (CFD), three main types of flow regimes exist: continuum, rarified, and free molecular. Of these regimes, the rarified regime is the most difficult to model because the continuum equations don't apply and using the Boltzmann equation is too computationally expensive to use. The Unified Flow Solver (UFS) is currently being developed to solve this problem by using the kinetic continuum Euler equations where valid, and only using the Boltzmann equation where necessary, thus reducing the computational cost. The use of the kinetic Euler equations helps to aid in the coupling of the Euler equations with the Boltzmann equation. This work compares UFS with a common nonequilibrium solver, LeMANS, to attempt to validate the thermo-chemical Euler solver available in UFS. Three types of simulations were run to validate the Euler solver: perfect gas, thermal nonequilibrium, and thermo-chemical nonequilibrium. The perfect gas simulation was run using both a monatomic and two species diatomic gas. The thermal nonequilibrium simulation was run using a 2 species gas, while the thermo-chemical nonequilibrium simulation was run using a 2 and 11 species gas. The results of the simulations show that UFS matches closely for both the monatomic and 2 species perfect gas simulations as well as the thermal nonequilibrium simulation. The thermo-chemical nonequilibrium simulations do not show the correct vibrational temperature, which causes the species concentrations to be incorrect. All of the simulations show that UFS is much slower than LeMANS in number of cpu hours. This means that UFS not a practical choice for a CFD solver and cannot be fully validated in its current state.

AFIT Designator


DTIC Accession Number