[jchawner]

Hello Sina:

Create connector(s) around the perimeter of each component of the airfoil. Connect the trailing edge of the slat to the leading edge of the main element and the trailing edge of the main element to the leading edge of the flap using connectors. The initial extrusion front (in 2D) will be a loop of connectors from leading edge of the slat around the entire collection and ending back at the slat leading edge. (Or you could do it from flap trailing edge. Doesn't matter.) Then create a domain by extruding from that front using the Normal/Hyperbolic technique.

Good Luck