Importance of nozzle geometry and plume expansion ratio on effective base drag

Base drag significantly influences the overall drag coefficient (Cd) of space launchers and depends on nozzle shape, base geometry, plume expansion ratio, and flight phase. This study employs RANS based CFDsimulations to investigate the impact of varying expansion ratios on aerodynamic performance. Two nozzle geometries are considered to reflect the diversity of design solutions encountered in propulsion systems. Simulations are performed under varying ambient pressures while maintaining a constant nozzle exit pressure, replicating conditions experienced during ascent. Results reveal different sensitivities to plume expansion ratio along the tested flight regimes.