To flip the local orientation of surfaces

To flip the local surface orientation of surfaces, use the following procedure.

The default orientation of a surface local coordinate system is determined by the order of the nodes that form the surface vertices and the plane of the surface. The edge formed by the first two nodes selected (i.e., N1 and N2) define the direction of the local x axis. This procedure reverses the nodal order of the surface incidences, thus redefining the local x axis and reversing the direction of the local z axis.

Select the surfaces you want to flip.
On the Surface ribbon tab, select the Flip Surface tool in the Edit group.

The local x is defined by the new N1 and N2 of the surface. The local z-axis of the surface points in the opposite direction. The local y axis of the surface changes according to the "right-hand rule."

You can edit surface incidences by selecting the Surfaces tool in the Surfaces group on the Spreadsheet ribbon tab.