To import a surface to ANSYS in the Design Modeler, you will first need to create just the surface using a CAD program, such as Solidworks. Note that these instructions also apply to importing any part or assembly from Solidworks to ANSYS; you just need to skip the step in Solidworks on adding Surfaces.
In Solidworks:
In ANSYS:
Now you should be able to see your surface in Design Modeler.
After you have created the geometry in Solidworks and saved it:
In ANSYS
Now you can edit your Geometry in Solidworks and refresh it in Design Modeler after you have changed it.
To refresh the geometry in Design Modeler:
Now your Geometry in Design Modeler will reflect the changes you made in Solidworks.
In Solidworks you can connect the geometry to Workbench:
ANSYS Workbench will then open with the Solidworks file attached:
Now you should be able to update your geometry in Solidworks and refresh it in ANSYS