Conditioned structure functions in turbulent hydrogen/air flames

Direct numerical simulation data obtained from two turbulent, lean hydrogen–air flames propagating in a box are analyzed to explore the influence of combustion-induced thermal expansion on turbulence unburned gas. For this purpose, Helmholtz–Hodge decomposition is applied computed velocity fields. Subsequently, second-order structure functions conditioned reactants sampled divergence-free solenoidal field or irrotational potential field, yielded by decomposition. Results show that significantly affects not only inside mean flame brushes but also upstream them. Upstream flames, first, transverse for velocities grow with distance [Formula: see text] between sampling points more slowly when compared counterpart entire field. Second, former growth rate depends substantially flame-brush leading edge, even at small text]. Third, root square (rms) increase decrease edge and comparable rms near edge. Fourth, although axial always close one another, thus implying isotropy reactants, exhibit high degree anisotropy. Fifth, effects substantial highly turbulent flame. These findings call development advanced models which allow discussed effects.