Experimental and simulation studies on spray characteristics of different injector configurations under supersonic incoming flow conditions

Experimental and three-dimensional simulation studies were performed to investigate the atomization of transverse jet injection under a freestream Mach number of 1.8, using circular, semi-circular, and square injectors. Systematic comparisons of initial spray patterns revealed distinct morphological differences among the three injector geometries. Detailed analysis was performed on the dynamic instability during jet initiation and the subsequent bow shock formation process. Particular attention was given to the recirculation zone developing, with its formation mechanism. Using zonal analysis, the global spray structure and flow field evolution were qualitatively characterized. Results show that higher injection pressure drops significantly increase the bow shock angle and spray penetration depth. Under equal pressure drops, circular injectors generated the largest bow shock angles and penetration depths, whereas semi-circular ones yielded the lowest. At constant mass flow rates, semi-circular injectors resulted in the highest bow shock angles and penetration depths, followed by square and then circular injectors. Analysis of droplet size distribution revealed a characteristic stratification pattern, with larger droplets concentrated at the core and smaller ones dispersed toward the edges. Injector geometry profoundly affected spatial distribution: semi-circular injectors demonstrate a noticeable narrowing effect in spray dispersion, whereas square injectors exhibit localized aggregation phenomena of larger spray particles within their spatial distribution. Droplet size measurements confirmed that square injectors produced larger Sauter mean diameters than the other geometries. Proper orthogonal decomposition analysis identified three dominant fluctuation modes: the first-order mode was governed by low-frequency oscillations, while the second and third modes exhibited streamwise shear-layer instabilities characteristic of Kelvin-Helmholtz vortices.