Numerical simulation of instabilities in lean premixed hydrogen combustion

Purpose - The present paper is about numerical simulations of one- and two-dimensional lean hydrogen combustion at an equivalence ratio of 0.7. The initial flat two-dimensional flames show unstable behavior. The instabilities generate flame wrinkling and flame induced turbulence. As a result cusp like structures arise that both merge and break up in new cusps. Therefore, physically, the laminar burning velocity associated to an adiabatic flat flame does not exist. Instead, a statistical effective burning velocity and flame width develop in which the cusp like structures and their effects are included. Our goal is to describe the phenomena with a reduced chemical approach. Design/methodology/approach - Simulations are performed with detailed kinetics, to study the main properties and dynamics of the wrinkling. An attempt is made to reduce the chemistry employing flamelet generated manifolds to make a step towards large scale, low cost simulations, which are still able to capture the physics. Here the manifold was built of premixed flames with variations of stretch, unburnt temperature and equivalence ratio. {\it A priori} correlations are presented together with results from actual reduced chemistry simulations. Findings - It was found that with introduction of variation of equivalence ratio into the manifold the main physical phenomena are captured. Moreover an effective inclusion of differential diffusion was succesfully tested and applied. Results of effective burning velocities and flame widths are presented. Originality/value - The paper shows the potential of performing accurate simulations using the chemical reduction technique of Flamelet Generated Manifolds for pure lean hydrogen flames.