To increase the degrees of freedom in post-processing, you may want to reverse the direction of the normal vector. A feature called Flip Normals can be used in Tgrid/Fluent Meshing. In FLUENT, it is possible to align normal vectors of internal faces, such as the interior, to a certain direction as required. However, we cannot decide which direction the normal vector can take. In that case, we will use TGrid’s /Fluent Meshing’s Flip Normals function. First, confirm the direction of the normal vector (please refer to the FAQ entitled “How do I find the sign of the mass flow rate of an internal face?”). Next, go to the Boundary > Manage… and enter the following settings. Options: select Flip Normals Face Zones: select the applicable internal face Click Apply and check if the direction of the normal vector has reversed. If there is no problem, save the mesh file. If the boundary conditions etc. have already been set, copy the settings (please refer to the FAQ entitled “How do I copy boundary conditions from one case to another?”).