Velocity and Pressure along Detonation Fronts - Image Processing of Experimental Results

摘要

This paper presents experimental results of hydrogen combustion. All experiments are premixed hydrogen and air at ambient temperature and pressure. The recorded high speed schlieren photographs are digitally processed to give a local velocity and pressure along the shock or detonation front. The image processing were done using an active contour method, and the properties along the front were calculated by the normal shock relations. The image processing method was tested against a case with uniform concentration and near constant detonation velocity. The processed results showed good agreement with the mixture CJ velocity. An experiment with stratified layer of reactants above an inert layer is also presented. The experimental results show that there is a curvature of the front, which is expected as the inert layer below the reactants were created by gravity current flow. The recorded pressure at the bottom wall was higher than the top wall pressure. The schlieren images were processed and showed that a bottom wall mach stem propagated with the same velocity as the detonation in the reactants. The same pressure behavior was seen in the image processed results. The pressure was however lower in the curved region. Previous numerical simulations showed that a change in cellular regularity could be expected, but it was not observed in the experimental results.