Numerical Aerodynamic Study of a BiCP-VTOL UAV For Wide Range of Angles of Attack and Sideslip Angles (EMERGENTIA project)

This article presents numerical analysis conducted on a Bi-rotor Convertible Vertical Take Off and Landing (BiCP-VTOL) Unmanned Aerial Vehicle (UAV) in order to validate the entire full aerodynamic flight envelope. The motivation behind these studies comes from the need of having precise aerodynamic models that will serve as benchmark where to test the innovative design presented within the EMERGENTIA project. The EMERGENTIA project (acronym for the full title: DevElopment of an unManned convERtible aircraft for rapid and efficient deployment in emerGENcy situationTIons) arises from the fact that emerging technologies are radically changing traditional operating procedures in disaster relief and emergency response management. For the numerical analysis, ANSYS 18.1 has been already used in order to have a first approach to the method, and, specifically, Fluent module to analyse the geometry and meshing previously generated.

Two different models of the BiCP-VTOL-UAV are studied, being the only difference that Aircraft 1 has a forward sweep wing of , while Aircraft 2 has a straight wing. The original full-size model had to be scaled in order to conduct the wind tunnel experiments, and, as this study is going to reproduce the exact same disposition, it will use the same dimensions: a 1:4 scale prototype that allows to make the blocking effects negligible. Also, the model’s geometry was originally designed in CATIA, so it needed several modifications to be adapted for the CFD analysis.

The wind tunnel is an open circuit one of 23.52 meters length, divided into three sections: contraction chamber, test chamber and diffuser, with a length of 5 meters and a rectangular section 1.4 meters wide and 1.8 meters high for the test chamber, and a maximum design speed of 30 m/s. The numerical analysis conducted in this paper will only focus on the contraction chamber, to reflect the same conditions as those measured during the experimental tests. For the numerical resolution, a structured mesh has been made and, after studying diverse turbulence model, the model with SST transition was finally chosen, which solves all the problems encountered with the other models, but raises the computational cost.

Some representative obtained results for the Aircraft 1 configuration and selected characteristic speed (10.69 m/s) will be presented. Also, sample values of lift and drag coefficients for alpha=10 deg are C_l=0.15681 and C_d=0.14499.