FLOW AROUND A CYLINDER - istiarto

– 5.13 –
within a greater number of time steps (n iterations) but within a smaller number of �- and
m-iterations. The total number of iterations in Test C (see Fig. 5.7) is considerably less
than that in Test B (see Fig. 5.6). The two strategies can be equally used for uniform flow
cases, but as can be seen later for flows around a cylinder, the strategy B does not always
converge whereas the strategy C does.
5.4.3 Conclusions
The numerical model developed previously (see Chapter 4) was tested to simulate a
simple flow case obtained from the experimental data of approaching uniform flow on a
smooth bed channel (Yulistiyanto, 1997). The test was done in order to validate the model
against a simple and well-known flow case. Three test runs using different boundary
conditions were performed. In Tests A and B, two distinct inlet boundary conditions were
used, i.e. a logarithmic and a uniform velocity distribution over the depth. In both tests,
the model performs quite satisfactorily. Comparison to the experimental data shows that
the agreement between the computed and the measured flow fields are quite satisfactory.
In Test C, the same boundary conditions as in Test B were used, but the pressure
convergence criterion and the surface positioning were changed. The convergence
criterion for the pressure computation was loosened, from 0.1 to 10 [Pa], but the surface
positioning was done only when the pressure computation shows a maximum pressure
correction of 0.01 [Pa]. The result of this test shows that this method can speed up the
computational time compared to Test B.
In all three runs, a stable computation is observed in the entire computation and a
convergence towards the steady-state solution is guaranteed.