**NUMERICAL PARAMETER INFLUENCE**

**ON BUMP TEST**

In
this part of the project, the study has been made with the test-case Bump
which will be describe later. We have tested particularly the influence
of two parameters: the CFL number and the artificial viscosity.

Their influence will be evaluated by looking at convergence of each
different calculation.

The Bump test is a computation
on half profile whose geometry is showed in the next figure representing

the mesh used for the calculation:

Unstrctured mesh used in Bump calculation.

Tests were made with the
Mach incidence number taken equal to 0.85 in every calculation.

The following figure represent the shock on the bump in one of our
tests:

Mach number evolution on the bump.

We will now study the influence of the cfl number and of artificial viscosity.

- CFL influence on convergence:

adimensional number is very important for the calculation. We have made two tests in order to study its influence on

the calculation. The following figure shows the results we have obtained with two different cfl numbers.

This figure shows that an increase of the cfl number improves the calculation speed. This result was expected. However, it is impossible to increase the cfl too much because it has a limit. Upper that limit the computation may diverge.

- Artificial viscosity influence on calculation:

this is not a physical parameter representing the phenomenom. Therefore it must be chosen with precaution.

The following figure represents two tests with different artificial viscosities.

By looking at this figure,
we can easily conclude that an increase of artificial viscosity improves
the

convergence of the calculation (about two orders in precision in this
case). Nevertheless, a too high artificial viscosity may disturbs the reality
of the physical problem. During the next tests, we will use an artificial
viscosity

equal to 0.2 because its precision appears efficient for our studies.