报告内容：

Recent developments show strong potential of micro air vehicles (MAVs) in a wide range of important surveillance functions, especially when hovering capability can be achieved. The capability of vertical takeoff/landing feature is also tempting; this capability not only provides for “perch and stare” monitoring but also for easy deployment/retrieval. Flapping flight of hummingbirds shows good examples of these capabilities. A lot of studies have been conducted to investigate the flight dynamics of hummingbird. Numerous researchers demonstrated the importance of the leading edge vortex (LEV) in enhancing lift production during hovering fight for a humming bird. Almost all of these studies were performed under steady inflow conditions without the presence of transient flow phenomena (e.g. gust). And yet, real-life ornithopters in the field have to routinely tackle gust and directional changes in the wind. In this talk, results of the flow field around a hummingbird wing under well-controlled gusty conditions are presented. In a water channel, using a 2-degree-of-freedom robotic hummingbird model mounted on a translation stage, conditions of gust impacting a wing were able to be mimicked. Phase-locked and time-resolved PIV measurements were obtained around the wing in the presence of gusts varying from 5-30% of the mean normal wing velocity. These measurements, in combination  with force and moment measurements using a six-component load cell, are used to understand transient flow phenomena induced by the gust, and  their effect on the net thrust and lift forces over a range of Reynolds number (2100<Re<30000). Results of the flow field show clear influence of gust to LEV and TEV evolution. From the lift and drag data, it is clear that the wing generates peak lift after the mid-down stroke. This agrees with the flow structures measured using a time-resolved PIV. At the phase of mid-down stroke the LEV is split into two vortices, the major vortex is still attached to the wing and the minor one sheds downstream. Immediately after that, the attached LEV starts to grow in both size and strength. The influence of gust to lift and drag production will also been discussed.

报告人简介: 

Fangjun Shu received his B.S and M.S. degrees from the University of Science and Technology of China in 1997 and 2000, respectively, and his Ph.D. degree from Purdue University in 2005. He is currently an assistant professor in the Department of Mechanical and Aerospace Engineering, New Mexico State University (NMSU). His research interests are in Experimental fluid dynamics, bio-inspired flow, biofluidics, microfluidics, turbulent flow, optical metrology and development of flow diagnostic methods.