Modeling of instationary turbulent combustion processes in hydrogen-air mixtures

One of the most important objectives in combustion research studies - either for technical applications or for safety aspects - is to obtain better knowledge of the interaction between the exothermic combustion process and the turbulent flow field, particular in hydrogen-air mixtures with a laminar burning velocity that is ten times as high as, for instance, the burning velocity of propane-air mixtures. We have studied the acceleration process of hydrogen-air flames by a numerical analysis based on the random vortex method and experimental validation. The algorithm models the turbulent eddy movement and provides information on the mechanisms of flame folding from the early phase after ignition to the propagation through different obstacle areas in tubes. The influence of combustion on the structure of the turbulence in the flow field and the effects of flow field instability on the flame development in tubes containing line or expanded obstacles are discussed. Numerical investigations of premixed hydrogen-air flame propagation behavior associated with vortex interactions due to a planar pressure wave crossing a curved flame front have been carried out. The results show a ''Tulip'' flame formation. Although the physical model is restricted by a number of idealizations, it displays however the essential features of large scale eddy flow associated with turbulent flame front effects observed experimentally by means of schlieren technique with the use of stoichiometric hydrogen-air mixture in our combustion tube.