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PRECOND - Pre-conditioning for low Mach number flows
This keyword may be used to apply matrix pre-conditioning to improve
(or allow) convergence for flows at low Mach numbers.
While it theoretically may be used at all Mach numbers, it increases
the CPU time required for each time step, and is therefore recommended
for use only when the Mach number is less than about 0.05.
The input parameter εpre is an artificial
The recommended value is
εpre = max (sqrt(3) M∞ , 0.2)
where M∞ is the freestream Mach number.
Very small values for εpre will lead to very large
values for artificial compressibility, and convergence problems,
especially when stagnation regions are present.
Values of εpre that are too large will decrease
the amount of pre-conditioning, leading to slow (or no) convergence.
Additional details on the implementation of the pre-conditioning
scheme, and results for various test cases, are presented by:
[Liu, Z. and Ramakrishnan, S. V. (2004)
"Preconditioned Upwind Schemes for Simulation of Low Speed Flows on Hybrid Grids,"
AIAA Paper 2004-1268]
This keyword may only be used when a physical time is specified with the
CFL# keyword, not a CFL number.
It also may not be used with the HLLE scheme
Last updated 1 Apr 2016