Why doesn't the Concorde have any wing fences? A Wing Fence is a straight, vertical "fence" running from forwards to backwards down the wing.



This MiG-17 has three fences per wing. I've also seen them on delta-winged aircraft such as the MiG-25.

The purpose of the wing fence is to prevent the air from flowing sideways over the wing. Air instead becomes trapped between the fences and flows front to back as normal. This is the ideal condition for creating lift, because the air follows the camber of the wing.

So why doesn't the Concorde have them?



The even more extreme sweep (at first) of Concorde's wing seems to me like it would induce even more sideways-flowing air, meaning it should benefit even more from wing fences.

(I noticed the Tupolev Tu-144 doesn't have them either.)
The main purpose of the wing fence is to prevent the boundary layer thickening in the wing due to the spanwise flow observed in swept wing, as can be seen below.



Image from fuckyeahfluiddynamics.tumblr.com

This is the reason for having wing fence in aircraft such as Mig-25- to avert stall and improve stability. In case of highly swept wing like the Concorde, this is not required as the mode of generation of lift is different- using vortex lift.



Vortices over the Concorde wing, Separation in three-dimensional steady flow, ONERA

In fact, there is a significant cross flow, as can be seen in the following image:



Flow above the Concorde Wing, Separation in three-dimensional steady flow, ONERA

Due to this, the wing fences are not required in case of highly swept wings like Delta and Ogival wings (as in Concorde), where separation leads to vortex lift. Mig- 25 wings, though highly swept, was neither of these- the wing generated lift by conventional manner.