Negative Cell Volume Alternative Solution
I am doing a CFD analysis for my major project in Mechanical Engineering.
I am supposed to improve a water driven motor that is build like a lobe pump.
I want to simulate a 3D domain using Fluent. The first problem to deal with was the limit of mesh cells in the student version of Ansys, while providing an acceptable orthogonal quality and skewness.
After adjusting the mesh, I ended up with 400k cells and a mesh quality which Fluent is not complaining about.
I am using an UDF for defining the rotation of the rotors in dynamic mesh and applying
the k-epsilon-model. I also set remeshing and smoothing.
However, after every iteration Fluent is remeshing and the total amount of mesh cells slightly increases, until the mesh cell limit is exceeded. Then the calculation stops and Fluent ends.
In the forum I read, that this issue can not be solved.
So, to decrease the initial number of cells, I cut down the domain more and more ending up with the following mesh.
When I simulate this geometry, the mesh cell number is fluctuating too, but I hope there is enough space to not exceed the limit.
Anyway, the problem now is that the calculation ends after a few iterations with an error message: “Negative Cell Volume”
What I found out is that an increase in the time step size should solve this problem, but with the current setting (picture below) it even takes one eternity to calculate some results so is there maybe another reason for this problem?
Here is a part of the log of the console until the error occurs. Might be a useful information for somebody.
I also carried out the field variable register as Kremella recommended at: https://forum.ansys.com/discussion/comment/103967#Comment_103967
Would be great to know if there is a chance to solve the negative cell volume problem, without further decreasing the time step size.
Furthermore, I would like to know what causes the fluctuation of the number of mesh cells.
I hope somebody has an idea to face this issue.