Rowan-Gollan-PhD-Thesis - Mechanical Engineering - University of ...

Chapter 6
Applications
In Chapters 4 and 5 the development work on models for thermochemical nonequilibrium was
presented; this chapter discusses the applications of that development work, that is, the range
of calculations which make use of the models for thermochemical nonequilibrium. At the very
beginning of the discussion (Section 1.4), it was stated that there were two direct benefits of
this thesis work: a longer term benefit, providing a foundation for modelling of radiating flow
fields; and an immediate benefit, the simulation of flows in impulse facilities. That immediate
benefit is the subject of this chapter: two “demonstration” calculations of expansion tube flows
are presented as examples of application of this work.
The work on modelling chemical nonequilibrium — the finite-rate chemistry model — has
had considerable use during the course of this project. At the beginning of this work, gen-
eral codes for computing the influence of chemistry in compressible flows were not widely
available or easily obtainable. 1 There were implementations of specific models, such as mod-
els for dissociating nitrogen or reacting air, but not generalised implementations to treat an
arbitrary mixture of gases. Yet over the years, the interest in reacting gases in the hyper-
sonic regime has continued to grow, now including mixtures containing carbon dioxide (the
atmospheres of Mars and Venus); hydrogen and helium (the Jovian atmosphere); and methane
and nitrogen (the Titan atmosphere). Thus a general chemistry code with easy user input was
a desirable addition to the local modelling capabilities. The implementation of a finite-rate
chemistry module as part of this work has been used in a number of calculations over the
course of this project: one-dimensional simulations of expansion tube flows (Stewart [172] and
Chiu [173]); two-dimensional (axisymmetric) simulations of expansion tube flows (Chiu [173],
Jacobs et al. [174], Scott [175], Brandis et al. [176] and Gollan et al. [177]); in the analysis of
results for radiation measurements on blunt bodies (Capra [178]); and as part of studies on
modelling turbulent boundary layers with heat release (Denman [179]).
More recently, the general thermochemical nonequilibrium model (finite-rate chemistry
with vibrational nonequilibrium) has been used in calculations of carbon dioxide flows in an
expansion tube facility (Potter et al. (2007) [180] and Potter et al. (2008) [181]). These are the
first CFD calculations to quantitatively assess the extent of vibrational nonequilibrium in the
test gas of an expansion tube flow.
1 This statement is still true at the time of writing.
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