Mixing enhancement mechanism induced by the cascaded fuel injectors in supersonic flows: A numerical study

The mixing process between the injectant and air in the supersonic flow is a crucial problem for the successful design of the scramjet engine, and it almost takes place simultaneously with the combustion process. In the current study, the flow field properties of the cascaded fuel injectors in the supersonic flow with the freestream Mach number being 3.75 have been investigated by means of the three-dimensional compressible Navier-Stokes equations coupled with the SST k-omega turbulence model, and the cascaded fuel injectors have been combined with the front hydrogen jet and the rear air jet. At the same time, the cascaded fuel injectors with pure hydrogen or nitrogen injection have been studied for comparison, as well as the single injection scheme with the same injector area. The obtained results show that the cascaded fuel injectors combined with the front hydrogen jet and the rear air jet are not only beneficial for the near wall mixing process, but also beneficial for the mixing augmentation in the whole flow field. The smaller injector space is not beneficial for the injectant penetration depth improvement, as well as the mixing augmentation. When the injector space is small, the injectant plume would extend downstream irrespective of whether the rear air jet exists or not, and its combustion flow field characteristics should be explored in the near future before it is used for engineering implementation.