Quenching of the flame at walls is modeled by a simple wall flux model [182]. The model assumes that the boundary layer for the flame surface density is thin such that the flame is unaffected by the wall until it contacts it. When a flamelet is touching the wall it will be quenched, resulting in a destruction of flame surface density at the wall.

The probability of a flamelet touching the wall is proportional to the fluctuation of the velocity component normal to the wall, , multiplied by a factor in order to account for a 50% chance for the fluctuation being directed towards the wall. This picture leads to a wall transfer coefficient equal to , or the equivalent wall flux for flame surface density:

(7–82)

where is the flame surface density at the internal near-wall boundary element center node. The sign of the flux is defined to be positive for flux in, and negative for flux going out.