Page 359 - Computational Fluid Dynamics for Engineers

11.7 Applications of INS2D 349

c*

m

200 400 600 800 1000
Fig. 11.13. Maximum residual ver-
Iteration Number sus iteration number.

400 600 1000
Iteration Number
Fig. 11.14. ci versus iteration number.

interfaces as information travels between zones, as well as the fact that the flow
tends to be unsteady at the thick trailing edge of the flap. This unsteadiness
causes the high-frequency oscillations in the lift as it converges to a steady-state
as can be seen in Fig. 11.14. The solutions are considered converged when the
maximum residual has dropped over 5 orders of magnitude and the lift coeffi-
cient has converged to 4 significant digits. The BB and SA runs have met this
criteria in 600 iterations, which required 16 minutes of CPU time on a Cray
C90 (or 27 minutes on a Cray YMP). The SST and DM take longer to damp
out the oscillations in the lift coefficient. They each take 900 iterations to reach