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Major scientific publication for ‘DESider’ project

The results of the EU-funded DESider project ('Detached eddy simulation for industrial aerodynamics') have been published in a new 454-page volume edited by Werner Haase, Marianna Braza and Alistair Revell. The book includes a comprehensive introduction to the project and full details of methods and approaches.

aircraft wingshot © Peter Gutierrez
New approach to turbulence modelling
© Peter Gutierrez

Computational fluid dynamics (CFD) uses numerical methods and algorithms to solve and analyse problems that involve fluid flows. In their preface to DESider – A European Effort on Hybrid RANS-LES Modelling, just published by Springer-Verlag, the authors quote a previous publication on the FLOMANIA project, which states, “In aircraft design, efficiency is determined by the ability to accurately and reliably predict the occurrence of, and to model the development of, turbulent flows. Hence, the main objective in industrial CFD is to… improve predictive accuracy for both complex flows and complex geometries."

While this statement remains valid, they continue, CFD is now under growing pressure to increase predictive accuracy while retaining 'affordable' computation times. "With an ever-increasing demand for faster, more reliable and cleaner aircraft," say the authors, "flight envelopes are necessarily shifted into areas of the flow regimes exhibiting highly unsteady and, for military aircraft, unstable flow behaviour. This undoubtedly poses major new challenges in CFD."

Improving on current methods

Reynolds-averaged Navier-Stokes (RANS) equations are the oldest approach to turbulence modelling. Together with highly resolved grids or 'meshes' employing millions of nodes, numerical methods such as RANS must have the inherent capability to predict unsteady flows. Statistically unsteady (or non-stationary) flows can be treated using 'URANS' methods, currently the CFD workhorses in the industry.

The DESider project focused on the development and combination of these approaches with much more expensive but more accurate 'large eddy simulation' (LES) methods. LES is a technique in which smaller eddies are filtered and are modelled using a sub-grid scale model, while larger energy carrying eddies are simulated.

Under the DESider project, 17 partners from the European Union, representing industry, research institutions and universities, and one partner from Russia worked to improve existing CFD methods.

The primary objective of the DESider project was to demonstrate the capabilities of these so-called hybrid RANS-LES approaches in the application to industrially relevant test cases with a focus on aerodynamic flows characterised by separation, wakes, vortex interaction and buffeting, i.e. flow features with the central common theme of inherent unsteadiness. An additional goal was to demonstrate the extent to which hybrid RANS-LES methods can be applied to multi-disciplinary topics such as aero-acoustics (noise reduction) and aero-elastics (reduced A/C weight, unsteady loads, fatigue issues, improved A/C safety), thus providing further tools towards more accurate and cost-effective design.

Successful collaboration

The authors also say, “All the goals achieved during the DESider project and described in this book have resulted from what has been a highly successful co-operation between European industries, research establishments and universities, leading to much improved knowledge dissemination and achieving cross-fertilisation between the various represented engineering industries; airframe, helicopter, power generation, car and train industries.

"This close collaboration, stimulated by the financial support from the European Union, can quite genuinely claim to have promoted and accelerated the enhancement of CFD approaches of each DESider partner to a far greater extent than would have otherwise been possible with the partners functioning individually in isolation."

The authors say they hope the chapter on hybrid RANS-LES methods, the newly developed turbulence models and the assessment and validation of methods based on a variety of test cases in particular will help seed and motivate further and extended future investigations and validation work.

The new book is part of the Springer-Verlag series ‘Notes on Numerical Fluid Mechanics and Multidisciplinary Design’, in which the results of many EU-funded projects have been published since 1993.

The book is now available online at: link