Characterization of milkweed-seed gust response

Inspired by the reproductive success of plant species that employ bristled seeds for wind-borne dispersal, this study investigates the gust response of milkweed seeds, selected for their near-spherical shape. Gust-response experiments are performed to determine whether these porous bodies offer unique aerodynamic properties. Optical motion-tracking and particle image velocimetry (PIV) are used to characterize the dynamics of milkweed seed samples as they freely respond to a flow perturbation produced in an unsteady, gust wind tunnel. The observed seed acceleration ratio was found to agree with that of similar-sized soap bubbles as well as theoretical predictions, suggesting that aerodynamic performance does not degrade with porosity. Observations of high-velocity and high-vorticity fluid deflected around the body, obtained via time-resolved PIV measurements, suggest that there is minimal flow through the porous sphere. Therefore, despite the seed’s porosity, the formation of a region of fluid shear, accompanied by vorticity roll-up around the body and in its wake, is not suppressed, as would normally be expected for porous bodies. Thus, the seeds achieve instantaneous drag exceeding that of a solid sphere (e.g. bubble) over the first eight convective times of the perturbation. Therefore, while the steady-state drag produced by porous bodies is typically lower than that of a solid counterpart, an enhanced drag response is generated during the initial flow acceleration period.

Vibration behavior of an overhead conductor under updraft winds

At present, the wind-induced response analysis of an overhead conductor is mainly based on the action of horizontal normal wind. However, for crossing hillsides or extremely strong winds, such a conductor will bear the action of updraft wind, which will change the geometry of the conductor and make its structural dynamic characteristics nonlinear to some extent. In this work, the in-plane and out-of-plane two-dimensional nonlinear equations were established under the action of self-weight and updraft wind. Furthermore, the improved equations of conductor tension and sag were obtained, and the wind-induced vibration response was further investigated. The results showed that the updraft wind caused the nonlinearity of the tension and sag of the overhead conductor, and the nonlinear geometric change significantly affected its resonance response, which exceeded 25% if the wind speed was 50 m/s. In addition, because the proportion of the resonance response in the total wind-induced response was different, the influence of the wind attack angle calculated using the gust response factor method on the gust response factor was slightly larger than that calculated using the the American society of civil engineers method.

Efficiency evaluation of energy harvesting from discrete gust response for plate wing

Gust response of aircraft can become a potential energy source thanks to energy harvesting (EH) methods, one of which can transform mechanical energy to electrical energy, applying piezoelectric ceramic transducers (PZTs). Harvested electrical energy needs to be evaluated for reuse, but current beam-model-based evaluation methods of EH performance for a plate model are insufficient because the plate is two-dimensional. This paper proposes two types of EH evaluation methods to analyze the gust exciting low-aspect-ratio plate wing model. One method focuses on the ratio of electrical energy to kinetic energy, and the other reflects energy output density per unit weight. These two methods can reveal the higher energy harvesting efficiency positions when utilizing PZTs on the flight EH system. Plate model, three-dimensional doublet lattice unsteady aeroelastic method and piezoelectric equation are used to build piezoaeroelastic wing model, and 1-cosine discrete gust load is the base excitation. A time-domain aero-electro-elastic state-space equation of the low-aspect-ratio piezoaeroelastic plate wing model is established, and the time-history analysis is used to solve the EH output. Results show that EH outputs are influenced by various parameters including load resistance, PZT thickness, gust intensity and wavelength, and PZT location variation. The optimal values of the proposed EH efficiency evaluation methods are found and explained.

Design and development of a vortex ring generator to study the impact of the ring as a gust

ABSTRACTWe present a simple method to generate discrete aerodynamic gust under controlled laboratory condition in the form of a vortex ring which, unlike conventional methods of perturbation, is well studied and highly controllable. We characterized the flow properties of the vortex ring using flow visualization and novel light bead method. Reynolds number of the vortex ring, based on its average propagation velocity and nozzle exit diameter, was 16000. We demonstrate this method by studying the impact of head-on gust on freely flying soldier flies, Reynolds number of which, based on its wingtip velocity and mean wing chord, was 1100. We also present simple theoretical models to characterize the vortex ring based on generating conditions. The device can also be used to generate continuous gust in any direction and can be applied, in general, to study the gust response of natural fliers and swimmers, man-made micro aerial vehicles and aquatic plant lives.