Design and Investigation of a Three-Dimensional TBCC Exhaust System Operating at Mach 0–6

This study presents the design and investigation of a three-dimensional (3D) turbine-based combined cycle (TBCC) exhaust system operating across Mach 0 to 6. The streamline tracing technique is utilized to design the 3D asymmetric nozzle for the cruise condition, followed by the application of a trimming method to enhance the aerodynamic performance and reduce the weight. A variable-geometry scheme, involving the rotation of the shared surface around its endpoint, is employed to regulate the mass flow rate (MFR) through the low-speed flow path (LSF) nozzle, with its nondimensional axial length optimized at 0.6250. Numerical simulations are conducted to analyze the flow characteristics and performance of the designed exhaust system. The results reveal that the flow is relatively simple during the separate operation of either the LSF or high-speed flow path (HSF), while the complex interaction between the LSF jet and HSF plume dominates the actual expansion ratios of the two flow paths during the parallel operation. The thrust coefficient gradually increases at low flight Mach numbers without any indication of a thrust trap. Additionally, after the mode transition is completed, the thrust coefficient exhibits a trend of initially increasing and then decreasing, driven by the transition of the operational condition from overexpansion to ideal expansion and finally to underexpansion. In summary, a stable variation in the thrust coefficient is demonstrated across the entire flight range.