Computational study of the effect of dimples and bumps on an unmanned aerial vehicle wing, configuration optimization and comparison with experimental wind tunnel results

• Main Author: Δημητρόπουλος, Δημήτριος
• Other Authors: Dimitropoulos, Dimitrios
• Language: English
• Published: 2023
• Subjects: Aerodynamics; UAV; Boundary layer; Separation; Passive control; CFD; Poly-Hexcore; Αεροδυναμική; Οριακό στρώμα; Αποκόλληση; Παθητικός έλεγχος

The climate crisis and the environmental degradation that have emerged in recent years have made the reduction of the aviation industry’s carbon footprint, via the aerodynamic optimization of aircrafts, a very important research topic. The aim of the present work is to improve the aerodynamic performance of the ethERAS UAV wing, by delaying the separation of the boundary layer on its suction surface using dimples and bumps. These modifications are a means of passive boundary layer control, which have been mainly used in golf balls. Their function is based on introducing instabilities and turbulent fluctuations to the flow, which lead to larger momentum transfer to the boundary layer, enabling it to travel longer distances, even under the effect of large adverse pressure gradients. To determine the optimal size and position of the modifications, five configurations were designed for each modification type, resulting in a total of ten configurations. All CAD models were created using DASSAULT SYSTÈMES Catia. Afterwards, the models were prepared for the computational simulations using ANSYS Spaceclaim. All wing designs, including the original, non-modified wing, were studied at a low velocity (7m/s), to simulate landing conditions. From this case study, the best performing configuration for each modification type was chosen. The two chosen configurations and the original, non-modified wing design were studied at cruising speed (27m/s). The computational grids were created in ANSYS Fluent Meshing, using the Poly-Hexcore method of the ANSYS Mosaic Meshing technology. The computational simulations were implemented using the ANSYS Fluent pressure-based solver, the SST k-omega (SST k-ω) turbulence model and second order spatial discretization schemes. The numerical results of the 7m/s case study were validated using experimental, wind tunnel data. The two chosen configurations from the 7m/s case study and the original, non-modified wing were 3D printed on scale of 1:4 and were used for the experimental study. The comparison of the computational and experimental results showed good agreement. From the overall study it was concluded that the use of dimples aided in the enhancement of the aerodynamic performance of the wing, by improving its aerodynamic efficiency. The use of bumps proved to be inconsistent, leading to the overall degradation of the aerodynamic performance.