RBF-based aerodynamic optimization of an industrial glider

Emiliano Costa


Gregor Veble, Matej Andrejasic

Pipistrel, Slovenia

Corrado Groth, Marco Evangelos Biancolini

University of Rome “Tor Vergata”

Ubaldo Cella

Design Methods


The present paper is addressed to the improvement of the aerodynamic design of an industrial glider flying at Mach 0.08. The original design suffers of a large separation occurring in the wing/fuselage junction region at high incidence angles. Adopting a numerical optimization approach, the separation was significantly reduced updating the local geometry of fuselage and fairing whilst maintaining the wing airfoil unchanged. Shape variations were applied to the glider’s baseline configuration through a mesh morphing technique founded on the mathematical framework of radial basis functions. The computational outputs were obtained employing a combined use of DesignXplorer™, Fluent® and RBF Morph™ software working in the ANSYS® Workbench™ environment. The
k-ω-SST turbulence model was used with two levels of structured hexahedral meshes, both generated using ICEM CFD™: a coarse grid, with 1.3 million of cells, to be used applying wall functions, and a fine version (6.8 million of cells) with a cells clustering aimed to solve the boundary layer up to the wall. The purpose to duplicate the study through the two approaches is to confirm the strategy’s validity of reducing the computational cost both modelling the boundary layer and reducing the dimension of the grid, using the fine grid only to verify the final solution. Two shape modifiers were set-up by means of RBF Morph to drive shape morphing guaranteeing, at the same time, the fulfilment of the manufacturing constraints. Once the RBF solutions were computed and made available, an optimization calculation was set up using DesignXplorer and, after performing CFD runs through Fluent, the potential optimal candidates maximizing the aerodynamic efficiency were identified by means of the surface response approach. A relevant aerodynamic efficiency improvement was finally gained in correspondence of the selected optimal design point. Such an optimization study is part of an explorative set of analyses that aimed at better addressing the numerical strategies to be employed in the development of the EC FP7 Project RBF4AERO.