Generating three-dimensional databases to optimize the aerodynamic flow of multi-element airfoils

Multi-element airfoils are commonly used in commercial aircraft to enhance their lift during takeoff and landing. These airfoils consist of a main profile and additional flaps or slats that can be adjusted separately to optimize for aerodynamic flow. Despite their increasing applications to other industrial developments, such as wind turbines, understanding the complex flow physics of these airfoils remains a persistent challenge.

Wang et al. specifically investigated the physics of the laminar-to-turbulent transition in the multi-element airfoil configuration. Their objective was to generate a highly accurate, 3D database to “elucidate the transition of the boundary layer over the airfoil from a laminar to a turbulent state from the perspective of vortex dynamics,” said author Suad Jakirlić.

Authors approached the problem by formulating a sensitized Reynolds-stress model which solved transport equations for the residual stress tensor, enabling the resolution of turbulent fluctuations. This allowed them to extend the conventional unsteady Reynolds-averaged Navier-Stokes framework to a scale-resolving simulation.

Ultimately, the authors’ approach not only generated the desired database, but their computational model, which did not involve an explicit grid-spacing parameter, showed how unstructured grids with relatively low densities could maintain reliable predictions at affordable computational costs. The results also provided computational evidence of wake-triggered secondary vortex pairs — significant in understanding the transition.

In the long term, the insights gained in this research could support the optimization of “multi-element airfoils for low-Reynolds-number aerial vehicles designed for applications within low-altitude economy,” said Jakirlić. It also shows “promise for other engineering applications by providing a balance between predictive accuracy and computational cost.”

Source: “A wake-triggered double-secondary-vortex topology over a multi-element airfoil: A sensitized Reynolds stress model study,” by Jiang-Sheng Wang, Sebastian Wegt, Robert Maduta, Jin-Jun Wang, and Suad Jakirlić, Physics of Fluids (2026). The article can be accessed at https://doi.org/10.1063/5.0353039 .