Galilean invariance flame test problem. Color maps show the ¹²C mass fraction, with the top left panel showing the initial conditions. The boundary conditions are such that the initial composition is inflowing through the bottom at speed v _in and the flame is burning to the right at speed v _f . The top right panel is for v _in = 0 and v _f = v _l = 76 km s ⁻¹, i.e., laminar flame with no cross wind. The bottom two panels have v _in = 500 km s ⁻¹, with the left panel using v _f = v _l and the right v _f = 100 km s ⁻¹. The black lines in the bottom panels show the expected steady-state slope of the flame-ash interface. Neglecting curvature effects from the inflow boundary condition, the expected behavior is very nearly reproduced.