AUTHOR: Safwan Qamrul, Shohag Alam Apon
MENTOR: Md. Motiur Rahman
SUPERVISOR: Arif Md. Shahed Iqubal
PROGRAM: Bachelor of Science in Mechanical Engineering
DEPARTMENT: Department of Mechanical Engineering
INSTITUTION: International University of Business Agriculture and Technology
SUBMISSION: Summer, 2025
KEY WORDS: Rocket propulsion, Convergent-divergent nozzle, Compressible flow, Shock and expansion wave
ABSTRACT: Rocket nozzles play a critical role in determining the performance, efficiency, and cost of rocket engines by converting high-temperature combustion gases into thrust. While conical nozzles are simple to manufacture, they are relatively heavy and less efficient, whereas bell-shaped nozzles offer improved performance with reduced length and weight but require more complex design optimization. This study investigates the performance differences between conical and bell-shaped rocket nozzles using computational fluid dynamics simulations in ANSYS Fluent. A reference nozzle was first simulated to validate the accuracy of the numerical approach. Following successful validation, a bell-shaped nozzle was designed using isentropic flow relations and expansion ratio calculations, and subsequently refined through iterative simulations. The results indicate that the optimized bell nozzle achieves nearly the same thrust and specific impulse as the conical nozzle while being approximately 32% shorter in length. This reduction translates to lower structural weight, reduced material usage, and improved flow characteristics. The findings demonstrate that bell-shaped nozzles can provide equivalent performance with enhanced efficiency, highlighting their potential for more cost-effective and practical rocket engine designs.
CAD Model
Conical Nozzle
Bell Shaped Nozzle
Conclusion
A series of conical and bell shaped rocket nozzles are analyzed against theoretical quasi-1D predictions in this work in an attempt to determine which nozzle geometry presents the best overall performance / practical lowcost solution for aerospace
propulsion. The approach utilized the balance between analytical estimates with in depth CFD simulations thus providing a robust comparison for identically-boundary conditions.
Results show that AWS-operating conical and bell nozzles can be compared fairly well with quasi-1D theoretical values of Mach number, thrust, and specific impulse for various nozzle configurations, thus confirming the accuracy of the analytical model.
But despite having the advantage of simplicity and reliability, the conical nozzle shows higher divergence losses and geometry is also longer. On the other hand, the bell nozzle designed by Rao’s contour optimization method performed with nearly similar
performance levels as that of quasi-1D baseline and showed an overall reduction in length of about 32%. This reducing of length is directly translated into decreased material (volume) need and reduced structural weight, which is a major advantage in
aerospace applications where efficiency and payload are key.
The results confirm the aim of the study, i.e., systematic comparison in viewpoint to conical and bell nozzles with reference to quasi-1D predictions, a validation that bell nozzle is a better more efficient and practical choice. Our results are consistent with
previous findings (Saputra & Andria, 2021; Patil et al., 2020; Fernandes et al., 2023) where the slim bell nozzle has a better performance-to-length aspect ratio when compared to the rest of nozzles.
The bell nozzle is thus a refined equilibrium design, combining thrust efficiency with structural lightweighting, and it could find widespread use in future propulsion system development, where both performance and material-performance tradeoff are needed.
To conclude, this study offers verified and optimized nozzle design framework by linking theoretical analysis with advanced CFD. The results provide not only to academic research but also for practical aerospace engineering, a sustainable and efficient approach for the scaleable rocket propulsion system design.