Vortex-Lattice vs Doublet-Lattice Method

[Guy Deraspe]

I have seen explained in a few books what the Vortex-Lattice method is.
I have recently seen mentionned the Doublet-Lattice method in reference.
Can somebody give me a short explaination of the difference between both
methods.

Thanks

Guy Deraspe

[Mark Drela]

A constant-doublet panel has exactly the same
velocity field as a vortex-ring panel, so there
is really no fundamental difference between the
two methods.

There are some differences in implementation details,
however. Most documented VL methods place a horseshoe
vortex at the 1/4-chord location of each surface panel,
so that each panel has its own trailing vortices which
extend into the wake. No special treatment of the wake
is then necessary. Putting the vortex at the 1/4-chord
location allows accurate results with very few chordwise
panels. Just one or two chordwise panels are often sufficient.

Most DL methods put a constant-doublet distribution
on each surface AND wake panel. This is equivalent to
putting a ring vortex around the perimeter of each
panel rather than the 1/4-chord location. The requires
more chordwise panels to get the center of lift position
roughly correct. On the other hand, DL is more convenient
for unsteady flows, where the wake doublet strengths are
not constant and so the horseshoe vortex representation
is not very natural.

Mark Drela First Law of Aviation:
MIT Aero & Astro "Takeoff is optional, landing is compulsory"