Small Python script to convert from Plot3D into Gmsh mesh format. In general you'll need mesh in Plot3D format (script was tested with files from http://turbmodels.larc.nasa.gov) and Neutral Map File for boundary description (also available from NASA for 3D versions of the meshes).
$ p3d2gmsh.py [-o OUT_FILE] [-m MAP_FILE] P3D_FILE
P3D_FILE: name of file with the mesh
MAP_FILE: Neutral Map File (if omitted script will search for a file with
nmf extension and the name of mesh file)
OUT_FILE: name of output file (if omitted script will save a file with msh
extension and the name of the mesh file)