Flow physics of supersonic combustion in a grooved two-strut scramjet combustor: A computational approach

Scramjet engines offer immense potential for hypersonic transportation and reusable space launch systems, but face critical challenges in achieving efficient fuel–air mixing and stable combustion within extremely short residence times. To address these challenges, this study investigates a novel two-strut scramjet combustor design incorporating streamwise grooves to enhance vortex formation and mixing. Three groove geometries (circular, triangular, and rectangular) were integrated into the strut walls and evaluated using Large Eddy Simulation, coupled with Fast Fourier Transform and Dynamic Mode Decomposition (DMD) analyses to capture unsteady flow features and combustion dynamics. Results indicate that the grooved struts strongly influence vortex characteristics, ignition location, and overall combustion behavior. The circular and triangular grooves achieve rapid ignition, with 92.3% and 88.4% combustion efficiency, within 100 and 150 mm downstream of injection, respectively. Whereas, the rectangular groove required a longer ignition distance (∼170 mm) due to excessive fuel–air dilution. Although the rectangular groove produced the strongest streamwise vortices and highest circulation, it also caused flame spreading toward wall regions, resulting in greater total pressure loss (up to 11.16%) and elevated pressure oscillations (1.5–3kHz) as revealed by Power Spectral Density analysis. For the circular groove case, the flame remained anchored close to the strut base, which helped in reducing pressure loss and combustion oscillations, leading to stable performance. DMD analysis also showed clear differences in flow structures for each groove design; the triangular groove produced strong shear-layer interactions near the strut, while the rectangular groove showed delayed dominant flow modes mainly in the far wake region. Overall, current findings highlight that stronger vortices alone are not sufficient for improved performance; instead, optimal combustion performance in scramjets relies on stable and coherent vortex structures that interact effectively with the boundary layer, ensuring efficient mixing, stable flameholding, and minimal pressure and thermal oscillations