[Roland R]

Hello,

I would like to calculate a Large Eddy Simulation to the investigation of an aero acoustics problem in high speed compressible flow. The LES calculation was initialized from a converged transient SST result. The geometry is quite complicated, I am fully aware that the mesh should be more finer but I have very short time.

I applied tetra mesh, its quality is about 0.3-0.5 . The mesh is fine in the narrow cross sections but it’s coarse in the zones which is not investigated.

The time step is 1e-6 s. Based on the convergence history the residuals is OK, but the Mach number is unrealistic:

COEFFICIENT LOOP ITERATION = 15 CPU SECONDS = 2.018E+05
----------------------------------------------------------------------
| Equation | Rate | RMS Res | Max Res | Linear Solution
+----------------------+------+---------+---------+------------------
| U-Mom | 0.58 | 2.5E-05 | 5.9E-03 | 7.5E-04 OK
| V-Mom | 0.80 | 2.8E-05 | 1.3E-02 | 8.2E-04 OK
| W-Mom | 0.83 | 5.8E-05 | 1.6E-02 | 1.2E-03 OK
| P-Mass | 0.89 | 9.2E-06 | 3.8E-03 | 5.0 5.1E-04 OK
+----------------------+------+---------+---------+------------------
| H-Energy | 0.84 | 3.1E-05 | 1.2E-02 | 5.8 3.5E-08 OK
+----------------------+------+---------+---------+------------------
+--------------------------------------------------------------------
| Notice: The maximum Mach number is 4.458E+01.
+--------------------------------------------------------------------

I thought that this numerical error was caused by the mesh but based on the result the mesh quality is OK in the zone of the high Mach number. The error can be detected in various locations but it always is in one node. (not in a large area). This notice can be seen after every time step then the solver stops with „overflow”.

Could anybody help me to solve this problem?

Thanks in advance
Roland