The Aeronautical Journal September 2025 Vol 129 No 1339

Advanced Air Mobility (AAM) is a burgeoning sector of the Aerospace industry exploring new design concepts from multi-passenger vehicles to small uncrewed autonomous systems for observations. These applications also expand operations into airspaces that were not previously engaged in commercial operations. The compounding of these with traditional aerospace vehicles and operations requires accuracy in aerodynamic analyses.

Aerodynamics and its broader counterpart, fluid mechanics are, by definition, unsteady. Aerodynamics is erroneously characterised by some as a ‘mature’ field, not worthy of further research development. This is a flawed argument as some of the most difficult aspects of vehicle flight are rooted in the realm of unsteady aerodynamics, which is crucial to progress in the fields of aeroelasticity, flight controls and flow control, in particular for these new aerospace paradigms.

Before the start of the new millennium, the accurate solution of the Navier-Stokes equations to characterise separated flow aerodynamics and aeroelastic predictions with dynamic motion was not tractable due to the computational capabilities. The introduction of high-performance parallel computing clusters with the availability of sufficient computational memory, as well as significant investments in software development, have led to important breakthroughs in resolving complex unsteady problems across all aerospace platforms. Many of the unsteady aerodynamics scenarios that are of engineering interest also include flow separation, compounding the complicated physics.

In Advances in Unsteady Computational Aerodynamics with Separation, the 61st Lanchester Memorial Lecture, progress over the last quarter-century in resolving aerospace problems with unsteady aerodynamics and flow separation is reviewed. Given the broad topic area, focus is primarily on rotorcraft and some fixed-wing applications in the subsonic Mach regime. Computational advancements in both hardware and software are surveyed, including developments in turbulence and transition modelling. Specific applications are also examined, such as dynamic stall, gust interactions and flight in highly turbulent environments (ship-airwake, urban canyons). 

Future development of the field includes a focus on uncertainty quantification to realise the vision of certification by analysis. To attain these goals, machine learning (ML) tools will play a key role to analyse the large unsteady datasets created by these computational predictions. The role of artificial intelligence (AI) is promising. AI/ML embedded within wall-modelled or wall-resolved large eddy solvers can provide mesh and time step refinement or improve turbulence and transition without the current prohibitive computational requirements.  However, it is essential that these tools do not replace the fundamental engineering understanding of the causal physics of these complex problems. Rather, these advancements require enhanced knowledge of the physics to ensure that they are applied accurately and that the results are correctly analysed and integrated into the aerospace roadmap.

The paper Advances in unsteady computational aerodynamics with separation: The 61st Lanchester memorial lecture by Marilyn Smith appears in Volume 129 Issue 1339 of The Aeronautical Journal and is available open access.

The Aeronautical Journal has, for over a century, been the UK’s leading scientific and technical aeronautics Journal and is the world’s oldest Aerospace Journal that remains in production. Published monthly, The Aeronautical Journal draws upon the expertise and resources of The Royal Aeronautical Society providing a world-wide forum for authors from the UK and overseas. Research papers are solicited on all aspects of research, design and development, construction and operation of aircraft and space vehicles. Papers are also welcomed which review, comprehensively, the results of recent research developments in any of the above topics.

The Royal Aeronautical Society is the world’s only professional body dedicated to the entire aerospace community. Established in 1866 to further the art, science and engineering of aeronautics, the Society has been at the forefront of developments ever since.

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