Injection of a fuel into a supersonic flow and the subsequent mixing continues to be a problem of great interest. Numerical simulations of the transverse injection into a supersonic cross-flow, both in a wind tunnel as well as a model scramjet combustor have been carried out. The study aims to investigate the effect of injector port shape on the mixing of gaseous fuels. The effect of injector flow field on the jet-freestream interaction and the mixing performance, which has hitherto not been studied, is investigated in detail in the present work. Three-dimensional, compressible, steady Favre-averaged Navier-Stokes equations have been solved using the SST k-ω turbulence model.
Transverse injection of helium (surrogate for hydrogen) into a Mach 3 cross-flow through circular and wedge injectors have been investigated in Part I. Flow conditions of the injectors are matched to isolate the effect of injector geometry. Mach number contours inside the injector reveal the flow at the exit of the injector to be supersonic and not sonic, as it is usually assumed to be. Oil flow visualisation shows flow features such as a bow shock and separated flow regions around the injectors. Helium mass fraction contours on axial planes show the injectant plume and its spreading in the vertical and spanwise direction. Performance metrics such as penetration height and degree of mixing of the injectors have been compared. Results show that the circular injector has better mixing performance when compared to the wedge injector for the operating conditions considered. Results from the present calculations show reasonable agreement with experimental data from an earlier study.
Transverse, supersonic injection of hydrogen through a supersonic, diamond-shaped, wall mounted injector as well as an equivalent circular injector, into a Mach 2.4 supersonic crossflow have been investigated in Part II. Two equivalence ratios, namely, ϕ=0.3 and 0.5, which result in pure scram mode of operation, are considered. Oil flow images and Schlieren images overlaid with contours of hydrogen mass fraction are used to demonstrate that the fuel penetrates higher with the diamond injector and that the fuel issues out of a part of the injector only on account of the jet being over-expanded. The higher penetration leads to better near-field mixing but the mixing slows down in the far field. The circular injector exhibits more lateral spreading as a result of flow separation ahead of the injector. Although the penetration and the nearfield mixing are less, mixing continues farther downstream resulting in almost the same level as that of the diamond injector. Fuel plume outline, contours of local equivalence ratio and local mixing efficiency are used to obtain insights into the spreading and the mixing of the fuel.