Su-Wan CHOI, Min-Seon JO, Bu-Kyeng SUNG, Si-Yoon KANG, Jeong-Yeol CHOI
DOI Number: N/A
Conference number: HiSST-2025-150
This study presents the design and experimental verification of a Circular-to-Obround Shape Transition (COST) nozzle, proposed as a candidate configuration for scramjet combustors. Conventional scramjets are generally based on either axisymmetric or rectangular cross-sections, each with distinct advantages and drawbacks. Axisymmetric geometries provide structural efficiency and stable pseudo-shock behavior, while rectangular geometries facilitate effective mixing, visualization, and injector placement
but suffer from stronger boundary-layer effects and higher total pressure losses. To combine these advantages, an obround cross-section, composed of semicircular arcs and flat walls, was introduced as a novel alternative. The COST nozzle was designed to simulate high-altitude flight conditions, with exit Mach number 2 and static pressure 3 bar at the isolator entrance. Boundary-layer corrections were incorporated using Sivell’s method. Experimental validation was performed by connecting the nozzle to the Vitiated Air Heater (VAH) facility at Pusan National University. Cold-flow wedge tests with high-speed Schlieren imaging confirmed uniform exit flow, with measured Mach numbers slightly above the
design value due to boundary-layer effects. The results demonstrate the feasibility of the COST nozzle and provide reference data for future investigations of obround scramjet isolator and combustor flow characteristics.