Unexpected behaviour of timeVaryingMappedFixedValue
 

Hi Guys,

this is my first post but not my first experience with this forum. I worked on CFD since about 2 years and this forum was always a great source of usefull information. So thanks for all your great work here. Now I got an unexpected problem and I would be glad to hear some experiences and opinions.

I want to investigate the development of turbulence in time and space by calculating a direct numerical simulation (DNS). The geometrical setup is a simple channel. To avoid development of a boundary layer I use symmetry conditions on the "walls".

To generate the inlet conditions I previously ran a simulation with a pseudospectral code (hit3d) and extracted slices. I fed these slices into my channel domain by using the "timeVaryingMappedFixedValue" boundary condition for U. So far everything seems to be perfect. While postprocessing I got some unexpected behaviour of the turbulence on the inlet.

A closer look reveled a strange behaviour of the inlet conditions:

Timestep t1:
http://img801.imageshack.us/img801/7011/hit0005.th.pnghttp://img641.imageshack.us/img641/803/of0005.th.png
HIT Simulation ................... OpenFOAM

Timestep t2:
http://img140.imageshack.us/img140/1884/hit0525.th.pnghttp://img826.imageshack.us/img826/5605/of0525.th.png
HIT Simulation ................... OpenFOAM

The four pictures show the slice which is defined in the constants/boundaryData/inlet directory (called HIT Simulation) and the slice extracted from the inlet in the result file of openFOAM (called openFOAM) for two different time steps.

In timestep t1 you can see, that the pictures (respectively the velocity fields) are very simmilar. If you have a closer look you would see that the magnitude of the velocity is different: The velosity in the openFOAM solution is less than in the HIT slice.

Timestep t2 shows a complete reverse behaviour: It is still the same field, but the velocities in openFOAM are incrased compared to the HIT slice.

This is a very unexpectable behaviour (for me!). The grid resolution in the plane is in both cases 128² so I would exclude interpolation errors.

Did someone experienced problems like this? Do you have any idea what is going on while interpolating? Is there any other interpolation?

I would be glad to share more information if you need more.

Thanks in advance for your help.

Kopy

Hey Guys,

I would like to disable interpolation of the inlet conditions just to check if this is the reason for the damping of my velocity field.

Is it possible to disable the interpolation without touching the source code?

Solved my problem.
My physical setup caused a pressure gradient. The input data works just fine.

Hi Kopy,

could you explain me be a bit more about "My physical setup caused a pressure gradient. The input data works just fine. " ? What about your p-inlet? What BC did you use for outlet?