Anomalous moving pressure cube in the flowfield
 

Hi everyone,
I'm trying an unsteady calculation of a wing flying near the ground at a speed of 60m/s. The air is modeled as compressible ideal gass. The inlet boundary condition is mass-flow-inlet and the outlet boundary condition is pressure outlet. All other boundaries except for the ground are symmetry.
To my disappointment, I find that there are cube regions which seem to be originating from the outlet periodically moving upstream. The two pictures below show the pressure distribution of the ground and plane of symmetry at t=0.15s and 0.364s respectively. The region with deeper color is the anomalous region. Once such a region passes the wing, the surface pressure distributions of the wing shift. The pressure in the first two cubic regions are positive, then become negative in the third and forth regions and the magnitude seems to be decreasing. Does anyone know how to eliminate these regions? Thanks a lot~:)

Looks like reflections of pressure waves from the inlet and outlet boundary conditions.
Lately, some boundary conditions in Fluent were given an optional non-reflecting treatment.
You should use them and reconsider the initial solution of your simulation.
If the initial solution is far from the solution of the actual setup, the amplitude of the disturbances you see is higher.

Thank you very much, flotus1! I'll go check my boundary condition settings and try the non-reflecting treatment.