Aerodynamic characteristics of a bristled wing in low Reynolds number

Abstract

Unlike common insects with smooth membranous wings, microscopic flying insects such as thrips have a distinctive wing geometry known as a bristled wing. The bristled wing consists of a single main frame at the center, from which several bristles extend in all directions, with gaps between them. The thrips can fly in the air with bristled wings because of the low-Reynolds-number environment they reside in. In such the low-Reynolds-number flow, viscous shear layers developed along the surface of each bristle may develop thick enough to overlap each other, and as a result, they prevent flow leakage in the gaps of bristles. In the present study, the aerodynamic characteristics of the bristled wing are investigated for various situations where insects with bristled wings are likely to encounter in the natural environment. Considering the unsteady flapping motion of such a wing of thrips, we first consider the unsteady gap flow formations and aerodynamic force generations of a flapping bristled wing. Furthermore, we propose new dimensionless parameters that determine the aerodynamics force generations of a two-dimensional bristled wing in a uniform free stream, and in a gusty flow. For these situations, the theoretical approaches to estimate the drag and lift are investigated.