Dynamically stretching and retracting wingspan has been widely observed in the flight of birds and bats, and its effects on the aerodynamic performance particularly lift generation are intriguing. The rectangular flat-plate flapping wing with a sinusoidally stretching and retracting wingspan is proposed as a simple model for biologically inspired dynamic morphing wings. Numerical simulations of the low-Reynolds-number flows around the flapping morphing wing are conducted in a parametric space by using the immersed boundary method. It is found that the instantaneous and time-averaged lift coefficients of the wing can be significantly enhanced by dynamically changing wingspan in a flapping cycle. The lift enhancement is caused by both changing the lifting surface area and manipulating the flow structures responsible to the vortex lift generation. The physical mechanisms behind the lift enhancement are explored by examining the three-dimensional flow structures around the flapping wing. (C) 2014 AIP Publishing LLC.

[http://dx.doi.org/10.1063/1.4884130]

This work was supported by the National Natural Science Foundation of China under Project Nos. 10872201, 11232011, 11302238, and 11372331, and the National Basic Research Program of China under Project No. 2013CB834100 (Nonlinear science). Tianshu Liu would like to acknowledge the hospitality received at LNM during his visit, where he accomplished this work. The simulations were performed on TianHe-1. The authors would like to acknowledge the support from National Supercomputer Center in Tianjin. In addition, we would like to thank the reviewer for his/her constructive and meticulous comments.

The article was published as:

Wang SZ, ZX, He GW. Lift Enhancement By Dynamically Changing Wingspan In Forward Flapping Flight[J].Physics Of Fluids,2014,26(6):61903.