Hello! I am currently implementing the face based gradient calculation into a custom solver, very similar to the description in the wiki pages. However, I noticed that some Fluent meshes contain elements whose faces are non-plain. This creates troubles while calculating a good normal vector, and the gradient calculation is very wrong even with slightly non-flat faces. Currently, I define the normal vector as the mean of the opposing corners normal vectors (nodes 1,2,3,4: 0.5(21x23+43x41) )

Is there a more elaborate system of doing this?

Very nice greetings, and thanks a lot Bernhard

(Just for information, I use a face value that is calculated using the different material properties of the individual cells.)

split the face into triangles? each triangle has a unique normal vector.