An axial flow fan includes a hub rotatable about a central axis. The hub includes a front face and a cylindrical portion. The axial flow fan also includes a plurality of blades extending radially outwardly from the cylindrical portion of the hub, and an aperture through the front face of the hub. The aperture is at least partially defined by a first surface oriented non-parallel with the front face. The axial flow fan further includes a lip having a second surface adjacent the first surface that at least partially overlaps the aperture and provides a tortuous passageway through the aperture.