Numerical investigation on the impact of cavity position in a parallel injection scramjet combustor

This study numerically investigates the effect of the streamwise location of a lower-wall cavity on reacting flow in a hydrogen-fuelled scramjet combustor using two-dimensional Reynolds-averaged Navier–Stokes equations and the SST k – ω turbulence model. The upper-wall cavity is retained at a fixed position downstream of the strut, while the lower-wall cavity is placed at three streamwise locations to isolate the influence of cavity placement relative to the strut wake and the upper cavity. This controlled comparison addresses the limited understanding of how lower-cavity relocation modifies shock–boundary-layer interactions, recirculation, fuel–air mixing, combustion, and total-pressure loss in a dual-cavity DLR-type combustor. The results show that relocating the lower cavity downstream changes the shock-train structure and expands the fuel–air interaction region. Compared with the baseline configuration, the cavity cases achieve complete combustion over a shorter axial distance (approximately 25 % reduction, as estimated from the reported efficiency curves), while the additional shock interactions increase total-pressure loss by approximately 23 %. The results therefore demonstrate the trade-off between combustion enhancement and aerodynamic penalty and provide a comparative basis for selecting cavity location under the prescribed operating conditions.