Overview
Computational Fluid Dynamics (CFD) has become a key technology in the development of new products in the aeronautical industry. During the last years the aerodynamic design engineers have progressively adapted their way-of-working to take advantage of the possibilities offered by new CFD capabilities based on the solution of the Euler and Reynolds averaged Navier-Stokes (RANS) equations. Significant improvements in physical modelling and solution algorithms have been as important as the enormous increase of computer power to enable numerical simulations in all stages of aircraft development. In particular, better automation of mesh generation techniques due to unstructured mesh technology and a generalised block-structured grid approach with non-matching and overlapping grids resulted in the ability to predict the flow physics and aerodynamic data of highly complex configurations.
However, despite the progress made in CFD, in terms of user time and computational resources, large aerodynamic simulations of viscous high Reynolds number flows around complex aircraft configurations are still very expensive. The requirement to reliably achieve results at a sufficient level of accuracy within short turn-around times places severe constraints on the application of CFD for aerodynamic data production, and the integration of high-fidelity methods in multidisciplinary simulation and optimisation procedures. Consequently, enhanced CFD capabilities for reducing design cycle and cost are indispensable for industry. Finally on a longer term, advanced physical models like DES and VLES will be used for evaluating the envelope of the final design, but it becomes clear that the results with second order methods too often depend on the mesh which cannot be tuned sufficiently well, once more stressing the need for higher accuracy.
The main goal of the ADIGMA project was to further strengthen computational fluid dynamics (CFD) as a key enabler for meeting the goals of future air transportation by developing innovative numerical simulation techniques with significant improvements in efficiency, accuracy and reliability.
CFD has become a key technology in the development of new products in the aeronautical industry. Significant improvements in physical modelling and solution algorithms as well as the enormous increase of computer power have enable numerical simulations in all stages of aircraft development. However, despite the progress made in CFD, in terms of user time and computational resources, large scale aerodynamic simulations of viscous high Reynolds number flows are still very expensive and time consuming.
The ADIGMA project concentrated on technologies showing the highest potential for efficient higher-order discretisations. These are discontinuous Galerkin (DG) methods and continuous residual distribution (CRD) schemes. The main scientific objectives of the ADIGMA project were:
- Further development and improvement of key ingredients for higher-order space discretisation methods for compressible Euler, Navier-Stokes and RANS equations.
- Development of higher order space-time discretisations for unsteady flows including moving geometries.
- Development of novel solution strategies to improve efficiency and robustness of higher order methods, enabling large-scale aerodynamic applications.
- Development of reliable adaptation strategies including error estimation, goal-oriented isotropic and anisotropic mesh refinement and the combination of mesh refinement with local variation of the order of accuracy (hp-refinement).
- Utilisation of innovative concepts in higher-order approximations and adaptation strategies for industrial applications.
- Critical assessment of newly developed adaptive higher-order methods for industrial aerodynamic applications; measurement of benefits compared to state-of-the-art flow solvers currently used in industry.
- Identification of the best strategies for the integration as major building blocks for the next generation industrial flow solvers.
In order to concentrate effort, the ADIGMA project focused on two major innovative technologies:
- higher-order methods and
- reliable adaptation techniques.
They showed high potential to provide major achievements in CFD for aircraft design. Since the computational efficiency of higher-order methods is currently not compatible with the performance of classical lower-order methods, dedicated developments needed to be addressed to improve this situation and to overcome current limitations and bottlenecks.
Since ADIGMA aimed at novel computational strategies for future industrial applications, it was indispensable that industrial partners specify the requirements on next-generation solvers at the beginning of the project and carry out a critical assessment of the newly developed technologies at midterm and towards the end of the project. With the help of a highly skilled consortium, the ADIGMA project aimed at scientific results and algorithms/methods, completely novel in an industrial environment.
Funding
Results
The competitiveness of higher-order methods to standard finite volume solvers was demonstrated for airfoil computations and 3D in viscid or laminar flows around rather simple configurations. Only limited research activities were devoted to the discretisation of the RANS equations with higher order methods, and it became clear that this effort is still in its infancy. A dedicated effort towards the industrialisation of the different higher-order methods is required and in particular the understanding of the discretisation procedure needs to mature. Moreover, although work was carried out to mitigate the resource usage of higher-order methods, further research needs to be invested in the area of algorithm optimisation and complexity reduction. Although within ADIGMA various methods and strategies were investigated and further enhanced to improve the solver efficiency of higher-order methods, the development of memory and CPU efficient solvers for large-scale industrial relevant applications still remains a major challenge.
The main achievements of the collaborative research project ADIGMA were:
- Significant progress in the development of adaptive higher-order methods for aerodynamic applications with high scientific output.
- Unique approach for critical assessment of innovative methods for industrial use.
- Creation of a comprehensive data base for performance assessment of advanced CFD methods.
- Successful demonstration of the potential and capabilities of higher-order methods.
- Identification of limitations and research directions for further industrialisation of higher order methods as well as.
- Significant improvement of the collaboration between academia, research organisations and industry on advanced CFD methods.
Despite the significant progress, it has to be mentioned that many achievements are still far from industrial use.
Technical Implications
The ADIGMA project focused on the, so far, fragmented research in higher-order methods in Europe. It fosters the scientific co-operation between the universities, research establishments and the aeronautical industry. The transfer from innovative upstream technologies in CFD into the industrial design cycle will be significantly improved. ADIGMA will provide a major breakthrough in numerical simulation of high Reynolds flows and thus will be essential and indispensable to exploit fully the potential of computational fluid dynamics as the major source for determining data required to drive the aerodynamic design process.
Moreover, to support the design of advanced flow control technologies (mainly driven by ecological topics like noise, emissions and by economic (DOC) effects), very precise CFD solutions – fulfilling the needs of, for example, aero-acoustics and complex flow control physics – are the key enablers to reach the ACARE Vision 2020 oriented design goals. ADIGMA is an important cornerstone to support the competitiveness of both the European research community and European aircraft manufacturers. As a benefit, the developed algorithms and solution methodologies will not be limited to aeronautical applications but can also be exploited for flow simulation in general.