Domain interfaces should typically be placed midway between the rotor and stator for turbomachinery cases.
To avoid numerical errors, the aspect ratio of elements on the domain interface should be between 0.1:1 and 10:1, as measured by x/y in Figure 11.2: Element Aspect Ratio at Domain Interface.
Where circular domain interfaces exist, they must be axisymmetric in shape as shown in Figure 11.3: Impeller/Volute.
