The DESider project was motivated by the increasing demand of the European aerospace industries to improve analysis on turbulent, unsteady aerodynamic flows exhibiting massive separation. However, for complex, turbulent separated flows, RANS modelling has proved to be a poorly adapted approach. While LES has shown viable capabilities of resolving the flow structures, it is too costly to be used at the time of this project in aeronautical applications. To close the gap between RANS and LES, hybrid RANS-LES methods will be investigated, among which the detached eddy simulation (DES) serves as a basis.
The main DESider project objectives were:
- To investigate and develop advanced modelling approaches for unsteady flow simulations as a compromise between URANS and LES, which are able to produce LES-comparable results for real aeronautical applications, yet with less costly computational resources compared to LES for an employment in industrial design environments.
- To demonstrate capabilities of hybrid RANS-LES approaches in solving industrially relevant applications with a focus on aerodynamic flows characterised by separation, wakes, vortex interaction and buffeting, i.e. all flows which are inherently unsteady.
- To investigate further that RANS-LES methods can be well applied to multidisciplinary topics as there are aero-acoustics (noise reduction) and aero-elastics (reduced A/C weight, unsteady loads, fatigue issues, improved A/C safety), improving this as a cost-effective design.
- To facilitate co-operation between the European industries, research establishments and universities and to foster co-operation between the different industries (as there are airframe, turbo-machinery, helicopters and power generation, as well as turbo-engines and ground transportation) with the help of an 'observer group'.
Major studies performed in the course of DESider in terms of development and assessment of the turbulence-resolving approaches, include:
- investigation of a role of a background RANS model in DES in terms of accuracy and robustness,
- improvement of RANS-LES switching in DES and, particularly, elimination of premature switching which may occur inside the boundary layer with a grid that is not sufficient for the well-resolved LES,
- extension of SAS modelling to two-equation turbulence models and a thorough assessment of the SAS approach against standard URANS and DES methods,
- development of DES-based approaches for the near-wall treatment in LES which would enable DES application to flows without any separation zone,
- assessment of DES, RANS-LES hybrids, and SAS capabilities in aero-acoustics and aero-elastics analysis, i.e., proof-of-applicability of new models in multi-disciplinary design environments,
- development of a new experimental data base for channel flow, with measurements carried out by ONERA and data post-processing by University Lille. Results have been used to test the hybrid RANS-LES methods investigated in the DESider project. Furthermore, as added value (i.e. not funded totally by DESider), cylinder measurements in the critical regime were performed by IMFT. Data of the latter experiment have also been used and validated in the DESider project.
Work in the DESider project was split into four Work Packages:
- Work package 1 - General management,
- Work package 2 - Experiments,
- Work package 3 - Modelling,
- Work package 4 - Applications.
The main objectives that were achieved by gathering expertise from European experts in the field of aerodynamics, turbulence modelling and numerical analysis up to multi-disciplinary (aero-elastic and aero-acoustic) design, can be summarised as follows:
- Based on the previously developed DES approach, advanced modelling approaches were investigated and developed for unsteady flow simulations as a compromise between URANS and LES, which are now able to produce LES-comparable results for real aeronautical applications, yet with less costly computational resources compared to full LES for an employment in industrial design environments.
- The project demonstrated the capabilities of hybrid RANS-LES approaches in solving industrially relevant applications with a focus on aerodynamic flows that are characterised by flow separation, wakes, vortex interaction and buffeting, i.e. flows, which are inherently unsteady.
- It was further investigated that hybrid RANS-LES methods can be well applied to multi-disciplinary topics as there are aero-acoustics (noise reduction) and aero-elastics (reduced weight, unsteady loads, fatigue issues, improved safety), improving by this both a cost-effective design and increased predictive accuracy.
- The DESider project strengthened co-operation between European industries, research establishments and universities, fostered co-operation, improved dissemination, and achieved cross-fertilisation between different industries as there are airframe, turbo-machinery, helicopters, power generation as well as turbo-engines and ground transportation by setting up a so-called 'observer group'. The latter being a group of industries plus one additional university (Liverpool University), were linked to the project - but not paid by it. All observers were allowed to attend technical meetings and some of these observers even provided own results as a 'gift in return'.
All the findings made in the course of the studies were supported by application of the different approaches to a wide range of thoroughly selected generic and industrial test cases. Based on this, model limitations were established, best practice recommendations were formulated and, most important, the predictive capabilities of the in-house CFD codes of the partners, and in particularly industry, were enhanced significantly.
Concerning knowledge dissemination to the 'outside world', DESider had set up a first conference on 'Hybrid RANS-LES Methods', taking place on 14/15 J
Last but not least it should be mentioned that the DESider project made Europe and, hence, the European research community in the area of aeronautics, a world-leading group on the improvement and application of hybrid RANS-LES methods. Having pointed out that the results are of major concern for the aeronautics industry with respect to the improved predictive accuracy of CFD results, it should be of high interest not to spoil that leadership. This strongly supports the continuation - on European level - with activities on flow-physics modelling.
All DESider project results have been published by Springer as part of the NNFM series (Haase, W., Braza, M., Revell, A., 'DESider - A European Effort on Hybrid RANS-LES Modelling', NNFM, Vol.103, Springer-Verlag Berlin-Heidelberg, 2009).