The goal of the present study is to implement an algorithm capable of designing linear aerospike contours and develop a numerical investigation of the altitude adaptive behavior and performance of high enthalpy flow expanded with such contoured nozzle. The contour was designed using Angelino,s rapid method, targeting an exit Mach number of 4.16. An inviscid model and viscous model (employing the realizable k- $$\epsilon$$ϵ for turbulence) were considered and the results compared, showing that turbulent effects must be taken into account to properly simulate important flowfield aspects such as static pressure, static temperature, entropy and viscous losses. The specific impulse is used as the performance criterion and it was observed that it increased with altitude, with only a 2 $$\%$$% decrease from an ideal bell nozzle for an underexpanding operation, situation where a nearly axial exhaust plume is obtained. Conversely, when turbulent effects are taken into account, overexpanded conditions have the lowest specific impulse, being lower than a quasi-1D analysis and the inviscid case. The findings summit the advantages of the aerospike nozzle over conventional nozzles. Conventional nozzles not only typically struggle in underexpansion scenarios, but also have high side-loads in overexpansion, due to flow detaching from the nozzle’s wall. A further conclusion is that the realizable k- $$\epsilon$$ϵ turbulent model proved a reliable and fast tool to evaluate turbulent effects that characterize the aerospike flowfield.

This study presents a comprehensive analysis of contoured nozzle designs using the Method of Characteristics (MOC) and Fluent simulations. The study aims to compare the performance and flowfield predictions of these methods and explore the influence of various design param- eters on nozzle performance. Initial investigations validate the MOC algorithm’s accuracy against commercial software, highlighting its rapid computational capability despite limita- tions in handling real gas effects. Fluent simulations consistently predict slightly lower specific impulse values due to differing exit pressure predictions but align closely with MOC results in inviscid flow conditions. The research explores the role of the initial circular arc in defin- ing the nozzle’s expansion and straightening sections, finding that smaller circular arcs create larger property gradients, necessitating quicker expansions and leading to potential isentropic losses, which were almost imperceptible in the Fluent case, in fact, a more axial flow was deliv- ered. Variations in design parameters, such as the contour’s exit angle and cone nozzle fraction, demonstrate their impact on nozzle performance, with higher exit angles generally improving specific impulse, contrary to expectation. For some pairs of design options, longer nozzles al- low smoother expansions, resulting in lower average exit angles and improved specific impulse. The findings emphasize the contemporary relevance of the MOC for preliminary nozzle studies, highlighting the balance between accuracy and computational cost.

The optimization of rocket nozzle design remains critical for advancing the efficiency and performance of space propulsion systems. This investigation presents an in-depth analysis of supersonic nozzle configurations and their aerodynamic behaviors, with a specific focus on methodologies to design a contour capable of enhancing thrust by reducing losses under. Further concepts of compressible aerodynamics and CFD are also reported, compassing the state of the art in chapters 1 and 2 necessary to base the studies reported. Chapter 3 investigates traditional nozzle designs, specifically conical and bell nozzles, employing the Method of Characteristics (MOC) to compute their flow characteristics and optimize geometrical parameters for minimum length and maximum thrust efficiency. Various design contours, including parabolic and truncated ideal configurations, are evaluated for their applicability in diverse applications such as supersonic wind tunnels and propulsion systems.In Chapter 4, the research extends to advanced nozzle geometries, including aerospike, dual-bell, expansion-deflection, and multi-grid nozzles, each offering unique advantages in adapting to varying pressure environments. These designs are analyzed for their ability to mitigate under- and over-expansion losses, improved thrust coefficient, and enhance specific impulse. The studies emphasize the critical balance between design complexity, manufacturing constraints, and aerodynamic performance, establishing guidelines for integrating innovative design features into modern propulsion systems.Computational simulations and theoretical formulations underscore the effectiveness of improved MOC techniques and boundary-layer corrections in accurately predicting nozzle performance. The findings have broad implications for the development of propulsion systems in high-demand applications, including single-stage-to-orbit (SSTO) vehicles and hypersonic flight systems.

Conventional De Laval nozzles reliably produce thrust, but their divergent section poses the major design challenge. The contour of a bell nozzle can be traced with several philosophies such as thrust optimization parabolas (TOP) or truncated ideal compressed (TIC) nozzles. The major difference between the two enunciated contours lies on transient effects in overexpanding operation. In this study, the performance of the two contours and exhaust plume structures are compared for several pressure ratios simulating the operating conditions of an ascending vehicles. A high divergent angle at the exit is imposed at design and the results are compared to those of a cone nozzle, isentropic and Quasi-1D cases, showing that contoured bell nozzles suffer specific impulse losses due to a thicker boundary layer. Nonetheless, a lower than expected average angle allows that, near design conditions, the contoured nozzles have a higher specific impulse then if an isentropic expansion occurred, with the entire flow exiting with the design exit angle. The exhaust plumes show close resemblance to literature description, with the Mach disk concavity relating to oblique shocks and their interaction within the nozzle. The two contours show similar performances, with the TIC nozzle overperforming the TOP nozzle in overexpanding conditions near the design point, but with neither ever surpassing the cone nozzle performance.

The aerospace industry is a significant contributor to CO₂ emissions, necessitating inno- vative propulsion technologies. Rotating detonation engines (RDEs) offer higher thermal ef- ficiency than traditional deflagration combustion by utilizing detonation waves that travel az- imuthally at speeds up to km/s. This study presents a three-dimensional numerical simulation of a premixed hydrogen-air RDE, achieving stable operation with a single detonation wave. The flowfield development from ignition to stable operation is analyzed, focusing on ignition and in- jection processes, and comparing results with ideal Chapman-Jouguet (C-J) values. Challenges in modeling, such as computational resource limitations and achieving stable detonation, are addressed. The simulation successfully captured key flowfield structures, including detonation wave propagation, oblique shocks, and slip lines, with performance metrics (thrust: 940 N, spe- cific impulse: 179 s) aligning with literature. A hydrogen-oxygen mixture failed to sustain stable detonation, highlighting the sensitivity of RDE operation to fuel-oxidizer combinations. The study underscores the potential of RDEs for reducing fuel consumption by up to 20% while improving efficiency, though challenges like backflow and injection modeling remain. These findings contribute to advancing RDE technology toward practical applications, supporting the development of environmentally friendly propulsion systems.