Optimization and Computational Fluid Dynamics - Department of ...

10 Dominique Thévenin
Parameter 2
feasible but
non-optimal
configurations
POF: ensemble of all optimal solutions
in the sense of Pareto
unfeasible configurations
Parameter 1
Fig. 1.6 Schematic representation of the concept of Pareto Optimal Frontier
After having introduced these notions, the practical limits of CFD-O in
terms of computer requirements have to be discussed: what can be investigated
today using CFD-O, and how can it be done? In order to investigate
this point, the natural reference point for discussing the requirements in terms
of computing time (CPU) and computer memory is of course the corresponding
requirement for a single evaluation, i.e., for us one CFD simulation of the
considered configuration. Admittedly, each CFD evaluation will usually lead
to slightly different numerical costs (needed computing time and computer
memory), but the variations are normally negligible. On the other hand, the
typical cost of a single CFD evaluation depends tremendously on the considered
problem. Looking for example at the examples presented in the next
chapter of this book:
• one simulation of the burner considering multispecies transport and combustion
takes typically about 20 hours of computing time and 1.8 Gigabytes
(GB) of computer memory;
• one simplified simulation of the turbulent channel flows requires less than 5
seconds of computing time and 10 Megabytes (MB) of computer memory.
In other words, the computing times vary by 5 orders of magnitude and the
computer memory by 3 orders of magnitude. This is typical of what will be
found in practice: simple CFD problems can be solved within seconds on a
standard PC; high-end CFD problems can require weeks of computing times