Experimental Study on the Unsteady Aerodynamics of a Robotic Hawkmoth Manduca sexta model

Abstract

Time-course force measurement and time-resolved PIV studies were conducted in order to investigate unsteady aerodynamic characteristics. A dynamically scaled-up robotic wing model was operated underwater within the Reynolds number range of 7.4×103-similar to a hovering hawkmoth. In the stroke section, the tendencies of each CLwere substantially obeyed to the translational velocity profiles. This indicated the appositeness of the quasisteady estimation in the stroke phase. Also, the CLtraces in the rotational phase showed that the wing-wake interaction was a localized phenomenon that appeared in a temporally and spatially narrow section right after the stroke reversal. It was found that the wing-wake interaction was impacted by the rotational profiles, i.e. the level of the rotational velocity rather than the change of the translational profiles. The PIV results demonstrated that the vortical structures near the stroke reversal, which were clearly described the LEV of the previous stroke, the TEVs due to the wing rotation, and the LEV of the next stroke. Timeline vorticity distributions showed that the TEV1 was generated by the impulsive start of the wing rotation. Such structures pointed out that the characteristics of the wing-wake interaction were not associated with the LEV of the next stroke, but substantially related with the TEV2.