A comparison of rotating and flapping wings in highly compressible flows

• Comparison of flapping and rotating wings in compressible flows is presented. • Flexibility of flapping wing is considered. • Lift coefficient, lift-to-drag ratio and power factor are discussed. • Wing-wing interaction is discussed. Recently, flapping wings have been identified as a potential solution for future Martian unmanned aerial vehicles, due to their performance in low-Reynolds number and moderately compressible environments. This necessitates a comparison study between flapping wings, and proven rotary wing design for the unique, low-density Martian atmosphere. Here, such a comparison of equivalent flapping and rotating wing configurations is considered through numerical simulations, with an emphasis on lift generation and efficiency. In general, flapping wings generated sufficiently higher lift than their rotating counterparts at low Reynolds numbers, while rotating wings in general outperformed flapping wings in terms of the lift-to-drag ratio and power factor. However, there are exceptions to this: weakly flexible flapping wings at low aspect ratio ( Λ = 2 ) outperformed rotating wings in terms of lift generation and efficiency at Ma ≤ 1. Multi-rotating wing configurations are also considered to determine if wing-wing interactions have any improvement in the performance, finding that the average lift coefficient remains similar to the single rotating wing cases, despite significant changes in the temporal space. Overall, this study identifies that flapping wings have the ability to outperform their rotating counterparts in the Martian environment from an aerodynamic perspective.