Investigation of Expansion Characteristics of Convergent–Divergent Nozzles with a Variable Geometry Sudden Expanded Duct

In recent years, there has been a significant rise in research focused on estimating the base pressure (P_b) characteristics of convergent–divergent nozzles with sudden expansion regions. This study explores the use of geometrical parameters as a control strategy for nozzles experiencing abrupt expansion at supersonic Mach numbers within an axisymmetric duct. It focuses on four distinct novel expansion duct configurations: square nozzle (SN), step square nozzle (SSN), curved nozzle (CN), and double curved nozzle (DCN). In this work, the high-speed compressible flow investigation is carried out numerically using control volume method on the nozzle with a fixed area ratio (AR) and L/D nozzle. Standard k-ε turbulence model is used in the analysis to access the recirculation region formed near the nozzle walls. The recirculation zone directly influences the P_b and shock cell. For NPR range from 2 to 10, SSN and CN shows an increase in P_b, which further increases the thrust and decreases the base drag provided by the nozzle. The thrust performance analysis shows that at NPR 2, the SN configuration delivers up to 61.8% higher thrust than other nozzles, while at high NPRs (6 to 10), SSN and CN configurations exhibit superior performance with thrust improvements of up to 59.2%. It is also evident that the L/D of the nozzle is also an important parameter that impacts the P_b as well as expansion in the nozzle.