Effect of Geometric Confinement on Shock Train Dynamics in Axisymmetric Ducts

Shock trains are fundamental features of confined supersonic flows, characterized by successive shock–boundary layer interactions that facilitate a gradual deceleration from supersonic to subsonic conditions. While previous studies have extensively examined their sensitivity to back pressure, inlet Mach number, and boundary layer properties, the effect of duct geometry at a constant blockage remains less understood. This study investigates the effect of varying the duct aspect ratio (AR) defined as the ratio of major to minor axis of an elliptical duct, on the shock train dynamics. The aspect ratio AR is varied from 1.0 to 3.0 while keeping the cross-sectional area and upstream conditions fixed. Maintaining a constant cross-sectional area along with the same boundary layer thickness ensures that inlet mass flow rate and overall blockage remain nominally identical, thereby isolating the effects of shape-induced confinement. Simulations are conducted using embedded-boundary (EB) method combined with adaptive mesh refinement (AMR), allowing dynamic local refinement of regions containing shocks. Results show that increasing the AR significantly modifies the shock train structure. The number of discrete shock cells in the shock train decreases, and the leading shock front becomes progressively elongated along the duct's major axis while shrinking along its minor axis. The normal shock stem observed in the circular duct (AR = 1.0) nearly disappears at AR = 3.0. Despite these morphological differences, the wall pressure distribution shows minimal dependence on AR, and the total stagnation pressure loss also remains nearly unchanged in the range of AR considered. These findings indicate that although duct geometry strongly affects the internal shock structure, the overall efficiency of flow deceleration and pressure adaptation is largely insensitive to variations in duct's aspect ratio under fixed blockage conditions.