Dr. YongshengLian currently is an assistant professor in the Mechanical Engineering Department of the University of Louisville. He is the director of the computational fluid dynamic laboratory. Before he joined the University of Louisville, he worked at the University of Michigan and NASA Glenn Research Center. Dr. Lian got his Ph.D in aerospace engineering from the University of Florida. He got his master degree and bachelor degree in applied mathematics from the Chinese Academy of Sciences and ShanDong University, respectively. Dr. Lian’s research interests include computational fluid dynamics, fluid/structure interaction, two-phase flow and design optimization. His work has been supported by the U.S. Air Force, NASA, NSF, General Electric, and Hitachi.
Micro air vehicles (MAVs) are autonomous small flight machines that can perform missions such as surveillance, target tracking or bio/chemical sensing in confined or otherwise dangerous areas. Typically MAVs have a flight speed of 15 m/s or less, maximum dimension of 15cm or less and weight of around 100g. Due to their small dimension and low flight speed, MAVs operate in the low Reynolds number flow region which is characterized with laminar-to-turbulent transition, massive flow separation and vortical flow structures. These unique features encountered by MAVs challenge the vehicle design. In the study of MAV researchers have searched new ideas from the nature. The impressive flight performance of dragonflies has not escaped the attention of biologists or aerodynamicists. First, unlike traditional aircraft, dragonflies have corrugated wings. Second, dragonflies have two pairs of wings and can individually control each wing to achieve desired performance for different missions. In this talk we will first discuss the aerodynamic and structural features of corrugated wings. In the second part we discuss how dragonflies achieve their superior performance by changing the flapping mode. We conclude that the wing corrugation does not provide aerodynamic advantages at low Reynolds numbers (Re<1000) but instead it offers the structural advantages by increasing the bending moment to reduce the wing deformation. We also conclude that dragonflies generate the highest resultant force using the so called in-phase flapping mode during escaping and hunting but reach the highest efficiency using the out-of-phase flapping mode during cruising flight.