Flow Problems

Flow Problems: Reason and Handling

With no doubt, flow problems are the number one troublemaker in simulations (at least since the turbulence model got the smart trouble shooting implemented).

Flow problems are indicated by the ENVI-met message

Updating Flow:    Cancelled after XXX Steps
Warning:          Flow Module failed to convert Solution! Increase Border Grids!

where XXX is the selected maximum amount of iteration steps (normally 200, see Interface, Advanced Settings Panel).
This message indicates, that ENVI-met is not able to calculate an accurate wind field in the given model constellation. As a result of this, the model is not mass conserving at one or more points and will probably produce some kind of fatal error in the next few calculation steps.
Normally one or more of the following points are the reason for this problem:

1. The Model Height is not sufficient
2. The amount of Nesting Grids is not sufficient
3. The Model Geometry is too complex

In case of point 1 or 2, click on the link to hear more about the problem.
In case of point 3, there is no general solution. Probably your model domain is very fragmented. Try to change the resolution of the model, simplify it or check, if a Model Rotation might improve the situation!

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