3rd derivative, cell neiboring

Ludovic

Hi,

I need to implement a filter which needs the 3rd derivative of the velocity. My 1st idea was to use the trick with the gradient of UDS, but I need in this case to allocate 27 scalars, I think it´s a lot and I fear to need too much RAM memory for grids with millions points. So my 2nd idea is to caluculate myself the derivative, at least the 2nd order. I have designed a complete structured grid to make my work easier, but as Fleunt works with unstructured grid, I have to access nevertheless the neighboors of the cells. There is a command in UDF files to catch the 2 cells which a face belongs to. Is there someone who has already used this way of doing to know how the cells are numbered, and to be able for each cell to know its neighboors and to be able to calculate the differentiates?

thanks