Conceptual Study on a Scramjet External Nozzle in a Rocket-Based Combined Cycle Engine

To develop a Reusable Launch Vehicle (RLV) using airbreather like Rocket Based Combined Cycle (RBCC) engine, so called Easy-to-Handle Prediction Models (EHPMs) are required for each vehicle element, because the parametric and iterative processes are mandatory in the conceptual design phase. The EHPMs must have suitable prediction accuracy and execution time to perform the conceptual study. The present study subjected to the nozzle element what is called Scramjet External Nozzle (SEN). The two-dimensional physical modeling was performed based on wave method. The pressure wave interaction in the SEN and ambient flows was taken into account by computing slip boundary formation. The developed model was validated by wind tunnel test. Nozzle Pressure Ratio (NPR) was employed as the test parameter defining the expansion condition of the SEN flow. Comparison between calculation and experiment was made on the ramp wall pressure distribution and its integral value called pressure coefficient. The experimental validation demonstrated that the developed model estimated the SEN pressure coefficient within an error of 10 %. The conceptual study for the SEN was performed using the developed model. The baseline SEN geometry and condition were set assuming the SEN applied to the nozzle element in RBCC engine. The RBCC engine was equipped to the booster stage of the Two-Stage-To-Orbit (TSTO) whose mission was set to accelerate the orbiter stage up to Mach 12. The operation analysis showed that the downstream portion of the SEN had the potential to deteriorate the thrust-to-weight ratio due to impingement of cowl expansion waves on the ramp wall. In conclusion, some of the performance improvement methodologies were proposed focusing on the cowl expansion waves.