Effective adjoint approaches for computational fluid dynamics

Machine Learning in Aerodynamic Shape Optimization

This article examines the increasingly crucial role played by Computational Fluid Dynamics (CFD) in the analysis, design, certification, and support of aerospace products. The status of CFD is described, and we identify opportunities for CFD to have a more substantial impact. The challenges facing CFD are also discussed, primarily in terms of numerical solution, computing power, and physical modelling. We believe the community must find a balance between enthusiasm and rigor. Besides becoming faster and more affordable by exploiting higher computing power, CFD needs to become more reliable, more reproducible across users, and better understood and integrated with other disciplines and engineering processes. Uncertainty quantification is universally considered as a major goal, but will be slow to take hold. The prospects are good for steady problems with Reynolds-Averaged Navier-Stokes (RANS) turbulence modelling to be solved accurately and without user intervention within a decade – even for very complex geometries, provided technologies, such as solution adaptation are matured for large three-dimensional problems. On the other hand, current projections for supercomputers show a future rate of growth only half of the rate enjoyed from the 1990s to 2013; true exaflop performance is not close. This will delay pure Large-Eddy Simulation (LES) for aerospace applications with their high Reynolds numbers, but hybrid RANS-LES approaches have great potential. Our expectations for a breakthrough in turbulence, whether within traditional modelling or LES, are low and as a result off-design flow physics including separation will continue to pose a substantial challenge, as will laminar-turbulent transition. We also advocate for much improved user interfaces, providing instant access to rich numerical and physical information as well as warnings over solution quality, and thus naturally training the user.

/pdf/on-the-role-and-challenges-of-cfd-in-the-aerospace-industry-303nxmuogb.pdf

On the role and challenges of CFD in the aerospace industry

Since its introduction, the NASA Common Research Model has proved a useful aerodynamic benchmark for predicting computational-fluid-dynamics-based drag and aerodynamic design optimization. The mode...

https://arc.aiaa.org/doi/pdf/10.2514/1.J056603

Benchmark Aerostructural Models for the Study of Transonic Aircraft Wings

Robust aerodynamic shape optimization—From a circle to an airfoil

Three model problems associated with aerodynamic drag minimizations are studied. These test cases have been proposed by the aerodynamic design optimization discussion group, and they include an inviscid NACA0012 nonlifting airfoil, a viscous RAE2822 lifting airfoil, and a viscous lifting wing based on the NASA Common Research Model. Various optimization methods are used, including MDOPT, TRANAIR, SYN83, and SYN107. The resulting designed and associated baseline geometries are cross analyzed by several computational fluid dynamics codes, including OVERFLOW, TRANAIR, GGNS, and FLO82. Pathological issues are unveiled in both of the simple airfoil model problems. Designed geometries for the inviscid symmetric test case exhibit strong tendencies to permit nonsymmetric flow solutions. Designed airfoils for the viscous lifting case also support nonunique solutions and hysteresis loops at or near the design point in Reynolds-averaged Navier–Stokes and integral boundary-layer method simulations. These results prov...

Study Based on the AIAA Aerodynamic Design Optimization Discussion Group Test Cases

It has long been thought by many that separated flows violated the assumptions of integral boundary-layer methods coupled to inviscid flow solvers. In this paper, it is shown how to extend the transpiration theory of the equivalent inviscid flow to essentially arbitrary large separation regions. It is shown through computational examples that integral boundary-layer methods can indeed give useful results up to stall in some situations. The limitations of these methods are also discussed and compared to Reynolds-averaged Navier–Stokes methods.

Implementation of a Separated Flow Capability in TRANAIR

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Study Based on the AIAA Aerodynamic Design Optimization Discussion Group Test Cases

Implementation of a Separated Flow Capability in TRANAIR