We have computed all the case for a steady flow, it means that we are looking for a steady configuration of the flow. Unfortunately, such phenomenon such as eddy creation behind the structure are unsteady. The results can become steady with the add of an artificial viscosity but it influences the precision of the results.
We can visualize the results of the calculation with the
post processing software called dplot. Values such as the pressure, the
density, the Mach number, the velocity vectors are accessible.
Example of calculation with Mach=0.5:
We have computed a case with an incidence
equal to zero. If we look at the residuals, it appears that the calculus
is converged but with an incertitude due to unsteady phenomenon.
The artificial viscosity is set to a very low value and it is not supposed to have an influence.
The unsteady phenomenon can be observed visually (for example with the Mach number). This case is completely symmetrical, but we observe differences between the upper part and the lower part. This must be due to eddies that are created behind the engine.
Visualisation of the Mach number
We consider that this approximation
has only few effects on the calculus of the Mass flow rate. This calculus
is made at the inlet of the engine, it should not be influenced by the
Example of calculation with Mach=1.5:
In this case, there is always a shock in front of the engine. To be able to compute this flow, the code AVBP use an artificial viscosity that adapt the numerical scheme in region of high gradient to give an acceptable result. The precision of these results has to be verified.
The following graph shows the residuals for an incidence equal to zero.
Because of the artificial viscosity, the residuals are almosts constant after a certain number of iterations, which was not the case for the subsonic calculation.
Visualisation of the shock with the pressure:
The shock in front of the engine is easy to see, the color goes from light green to red. In the same time, we can visualize the depression at the back of the engine.
Visualisation of the pression and the grid
We can notice that the shock (from light green to red)
is thicker that what we have expected. It is due to the artificial viscosity
first that reduce high gradient and to the mesh that doesn't seem adapted.
The grid should be thiner in the front part of the engine.
Other Examples with an incidence of 15 degrees: