Implementation of aero-elastic capabilities in a LBM flow solver: application to a low-Reynolds rotor for micro-air vehicles

Abstract

Micro air vehicles (MAVs) are used both for civil (rescue missions) and military (surveillance, recognition) applications. However the aerodynamic performance of the propeller is known to be lower than for classical large rotors, due to leading edge vortex occurring at low Reynolds number flows. Such rotors can also exhibits a flexible behaviour due to the material used to build the blades, making the prediction of aerodynamic performance challenging for numerical flow solvers. A potential way to improve the rotor performance is also to take advantage of the flow unsteadiness, by imposing an unsteady forced motion, like a periodic variation of the rotor pitch. There is thus a need to develop aero-elastic capabilities in numerical flow solvers, which is the main objective of this paper. The method relies on the implementation of Fluid-Structure Interaction (FSI) capabilities in a Lattice-Boltzmann flow solver, in order to take advantage of the flexibility allowed by the immersed boundary approach. FSI capabilities are implemented in a monolithic fashion, using generalised coordinates to represent the blade as a flexible beam. Two sets of simulations are performed: a) with a forced motion and b) by coupling the flow with the equation of the dynamics. Results show that a forced motion has a good potential to increase the rotor thrust but significant improvements should yet to be done to reduce the over-power consumed by the forced motion. While dynamic flapping has a negligible influence on the flow, dynamic pitching has the potential to moderately modify the pressure distribution at the trailing edge. However its impact on the rotor performance is weak (less than 0.5% on the thrust).