For turbulent flow, the effective or turbulent burning velocity will differ from the laminar burning velocity,
. Typically turbulence will increase the burning
velocity, because wrinkling of the flame front results in an increased
effective flame surface. At very high turbulence, the opposite effect
may occur, leading to a decrease in the effective burning velocity
because of local extinction. A model is required to describe the turbulent
burning velocity as a function of laminar burning velocity and turbulence
quantities.
The burning velocity is defined relative to the unburnt fluid.
Relative to the burnt fluid, it will be higher by a factor equal to
the fluid expansion ratio, .