Large eddy simulation of aircraft at affordable cost: a milestone in computational fluid dynamics

While there have been numerous applications of large eddy simulations (LES) to complex flows, their application to practical engineering configurations, such as full aircraft models, have been limited to date. Recently, however, advances in rapid, high quality mesh generation, low-dissipation numerical schemes and physics-based subgrid-scale andwall models have led to, for the first time, accurate simulations of a realistic aircraft in landing configuration (the Japanese Aerospace Exploration Agency Standard Model) in less than a day of turnaround time with modest resource requirements. In this paper, a systematic study of the predictive capability of LES across a range of angles of attack (including maximum lift and post-stall regimes), the robustness of the predictions to grid resolution and the incorporation of wind tunnel effects is carried out. Integrated engineering quantities of interest, such as lift, drag and pitching moment will be compared with experimental data, while sectional pressure forces will be used to corroborate the accuracy of the integrated quantities. Good agreement with experimental C-L data is obtained across the lift curve with the coefficient of lift at maximum lift, C-L,C-max, consistently being predicted to within five lift counts of the experimental value. The grid point requirements to achieve this level of accuracy are reduced compared with recent estimates (even for wall modelled LES), with the solutions showing systematic improvement upon grid refinement, with the exception of the solution at the lowest angles of attack, which will be discussed later in the text. Simulations that include the wind tunnel walls and aircraft body mounting system are able to replicate important features of the flow field noted in the experiment that are absent from free air calculations of the same geometry, namely, the onset of inboard flow separation in the post-stall regime. Turnaround times of the order of a day are made possible in part by algorithmic advances made to leverage graphical processing units. The results presented herein suggest that this combined approach (meshing, numerical algorithms, modelling, efficient computer implementation) is on the threshold of readiness for industrial use in aeronautical design. Impact Statement The use of computational fluid dynamics for external aerodynamic applications has been a key tool for aircraft design in the modern aerospace industry. In take-off and landing configurations, predicting the maximum lift an aircraft can produce and the associated onset of boundary layer separation encountered at high angles of attack is critically important. Flow solutions from state-of-the-art solvers are unable to routinely comply with the stringent accuracy and computational efficiency requirements demanded by industry. Leveraging large eddy simulation with appropriate wall/subgrid-scale models and low dissipation numerical methods suitable for complex geometries on modern computer architectures offers a tractable path towards meeting these accuracy and affordability requirements.

Automated summary

This paper systematically studies the predictive capability of LES for a range of angles of attack, grid resolution, and wind tunnel effects. The results show reduced grid point requirements while maintaining accuracy, demonstrating potential for industrial use in aeronautical design.