Bristled-wing design of materials, microstructures, and aerodynamics enables flapping flight in tiny wasps

Enhancement of aerodynamic performance of a bristled wing by elliptic cylinders

Enhancing the aerodynamic performance of bristled wings is an important topic for small flying robotics. This paper numerically investigates this situation at very low Reynolds numbers by using elliptic cylinders as the bristles instead of circular cylinders. Optimal configuration of the bristled wing with five elliptic cylinders is obtained, which corresponds to the maximum lift. The results show that, compared with the case of circular cylindrical bristles, the aerodynamic performance of the elliptical bristles can be enhanced effectively. The enhancement can be more significant as the aspect ratio of the ellipses increases and the gap width decreases. The bristled wing generates more lift compared to a flat-plate wing with a length five times that of the major axis of an ellipse. For the cases that the attack angleαfor the whole wing is equal to those for the elliptical bristlesθ, the optimal attack angle for ellipses maximizing the total lift force of the five-bristle model is between 40° and 45°. Forα ≠θwith the Reynold numberRe≪ 0.1, the optimal ellipse attack angle is between 40° and 45°. Forα ≠θwithRe∼ 1, the optimal ellipse attack angle deviates heavier from the range between 40° and 45° at someαvalues and reaches approximately 32° atα= 20°. This paper can lay a foundation for optimal design of small flying robotics and enhancement of flow through porous structures in future.

Fluid-structure interactions of bristled wings: the trade-off between weight and drag

The smallest flying insects often have bristled wings resembling feathers or combs. We combined experiments and three-dimensional numerical simulations to investigate the trade-off between wing weight and drag generation. In experiments of bristled strips, a reduced physical model of the bristled wing, we found that the elasto-viscous number indicates when reconfiguration occurs in the bristles. Analysis of existing biological data suggested that bristled wings of miniature insects lie below the reconfiguration threshold, thus avoiding drag reduction. Numerical simulations of bristled strips showed that there exist optimal numbers of bristles that maximize the weighted drag when the additional volume due to the bristles is taken into account. We found a scaling relationship between the rescaled optimal numbers and the dimensionless bristle length. This result agrees qualitatively with and provides an upper bound for the bristled wing morphological data analysed in this study.

High stability in filtration apparatus of African shrimp

The African shrimp (Atya gabonensis) uses elongated setae to filter feed, adapting to high flow velocities. The setae's stability stems from carefully designed geometric and structural parameters, notably a specialized wall and distribution principle. This study highlights the robust filtration mechanism in the shrimp and potential for developing stable structures in underwater environments.

Design and research of soft-body cavity-type detonation drivers

According to the high-energy-density movement characteristics of animals during jumping, soft-body cavity-type detonation driver that combines the explosive chemical reaction mechanism of hydrogen and oxygen is designed, in order to control the robot in jump to achieve output optimization. Then, combined with the theoretical values of the detonation dynamic equation and experimental data for the performance parameters, the influences of the mixing ratio of hydrogen (H₂) and oxygen (O₂), the volume of mixed hydrogen and oxygen in the cavity, and the shape, wall thickness, and area ratio value of the soft-body cavity on the output performance of the detonation driver are analyzed. When gas volume is 20:10 mL, the jump height reaches 2.5 m. In addition, the upper and lower area ratio of cavity is optimized to 2:1, improving the output performance by 21.6% on average. Therefore, the above research results provide reference for the driver structure design of jumping robot.

Flow development and leading edge vorticity in bristled insect wings

Small flying insects such as the tiny thrip Gynaikothrips ficorum have wings with bristles attached to a solid shaft instead of solid membranes. Air passing through the bristle fringe, however, makes bristled insect wings less effective for aerodynamic force production. In this study, we quantified the ability of bristled wings to generate a leading edge vortex (LEV) for lift support during wing flapping, scored its circulation during wing translation, and investigated its behaviour at the stroke reversals. The data were measured in robotic model wings flapping with a generic kinematic pattern at Reynolds number of ~ 3.4, while applying two-dimensional particle image velocimetry. We found that aerodynamic performance due to LEV circulation linearly decreases with increasing bristle spacing. The wings of Gynaikothrips ficorum might thus produce approximately 9% less aerodynamic force for flight than a solid membranous wing. At the stroke reversals, leading and trailing edge vortices dissipate quickly within no more than ~ 2% of the stroke cycle duration. This elevated dissipation makes vortex shedding obsolete during the reversals and allows a quick build-up of counter-vorticity when the wing reverses flapping direction. In sum, our findings highlight the flow conditions associated with bristled wing design in insects and are thus significant for assessing biological fitness and dispersal of insects flying in a viscosity-dominated fluid regime.

Aerodynamics and three-dimensional effect of a translating bristled wing at low Reynolds numbers

The smallest insects fly with bristled wings at very low Reynolds numbers (Re) and use the drag of the wings to provide the weight-supporting force and thrust. Previous studies used two-dimensional (2-D) models to study the aerodynamic force and the detailed flow field of the bristled wings, neglecting the three-dimensional (3-D) effect caused by the finite span. At high Re, the 3-D effect is known to decrease the aerodynamic force on a body, compared with the 2-D case. However, the bristled wing operates at very low Re, for which the 3-D effect is unknown. Here, a 3-D model of the bristled wing is constructed to numerically investigate the detailed flow field and the aerodynamic force of the wing. Our findings are as follows: The 3-D effect at low Re increases the drag of the bristled wing compared with that of the corresponding 2-D wing, which is contrary to that of the high-Re case. The drag increase is limited to the tip region of the bristles and could be explained by the increase of the flow velocity around the tip region. The spanwise length of the drag-increasing region (measuring from the wing tip) is about 0.23 chord length and does not vary as the wing aspect ratio increases. The amount of the drag increment in the tip region does not vary as the wing aspect ratio increases either, leading to the decrease of the drag coefficient with increasing aspect ratio.

Efficiency and Aerodynamic Performance of Bristled Insect Wings Depending on Reynolds Number in Flapping Flight

Insect wings are generally constructed from veins and solid membranes. However, in the case of the smallest flying insects, the wing membrane is often replaced by hair-like bristles. In contrast to large insects, it is possible for both bristled and membranous wings to be simultaneously present in small insect species. There is therefore a continuing debate about the advantages and disadvantages of bristled wings for flight. In this study, we experimentally tested bristled robotic wing models on their ability to generate vertical forces and scored aerodynamic efficiency at Reynolds numbers that are typical for flight in miniature insects. The tested wings ranged from a solid membrane to a few bristles. A generic lift-based wing kinematic pattern moved the wings around their root. The results show that the lift coefficients, power coefficients and Froude efficiency decreased with increasing bristle spacing. Skin friction significantly attenuates lift production, which may even result in negative coefficients at elevated bristle spacing and low Reynolds numbers. The experimental data confirm previous findings from numerical simulations. These had suggested that for small insects, flying with bristled instead of membranous wings involved less change in energetic costs than for large insects. In sum, our findings highlight the aerodynamic changes associated with bristled wing designs and are thus significant for assessing the biological fitness and dispersal of flying insects.