Effects of Strouhal Number and Reduced Frequency on Aerodynamic Performance of a Flapping Wing-Fixed Wing Tandem Configuration

Micro air vehicles (MAVs) in flapping and fixed wings both have promising applications in both military and civil fields. Past studies have mainly focused on the aerodynamic performance and flow structure of a single flapping wing or a single fixed wing, and it is not clear whether benefit in propulsion performance enhancement can be got from the aerodynamic interaction between the upstream flapping wing and the downstream fixed wing. In this paper, the lattice Boltzmann method combined with the immersion boundary method is used to study the propulsive performance and flow structure of the tandem configuration, and the effects of Strouhal number (St) and reduced frequency (k) on the thrust and propulsive efficiency are investigated at Re = 500. The results show that most of the tandem configurations produce three rows of vortices, unlike the wake structure of a single flapping wing, i.e., von Karman vortex street. The propulsive performance of the tandem configuration is better than that of a single flapping wing within the current parameter range. As St increases, the thrust increases but the propulsion efficiency first increases and then decreases. The highest efficiency St range is around 0.7-0.8. The thrust increases and the propulsive efficiency decreases with k. Generally, the effect of St on propulsive performance is more significant. The research can provide guidance for the aerodynamic design of MAVs with combined flapping wing and fixed wing configuration.