title: Lift enhancement by bats' dynamically changing wingspan.
abstract: This paper elucidates the aerodynamic role of the dynamically changing wingspan in bat flight. Based on direct numerical simulations of the flow over a slow-flying bat, it is found that the dynamically changing wingspan can significantly enhance the lift. Further, an analysis of flow structures and lift decomposition reveal that the elevated vortex lift associated with the leading-edge vortices intensified by the dynamically changing wingspan considerably contributed to enhancement of the time-averaged lift. The nonlinear interaction between the dynamically changing wing and the vortical structures plays an important role in the lift enhancement of a flying bat in addition to the geometrical effect of changing the lifting-surface area in a flapping cycle. In addition, the dynamically changing wingspan leads to the higher efficiency in terms of generating lift for a given amount of the mechanical energy consumed in flight.
authors.affiliation: The State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China.
authors.forename: Shizhao
authors.initials: S
authors.lastname: Wang
authors.affiliation: The State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China.
authors.forename: Xing
authors.initials: X
authors.lastname: Zhang
authors.affiliation: The State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China hgw@lnm.imech.ac.cn.
authors.forename: Guowei
authors.initials: G
authors.lastname: He
authors.affiliation: The State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China Department of Mechanical and Aerospace Engineering, Western Michigan University, Kalamazoo, MI 49008, USA.
authors.forename: Tianshu
authors.initials: T
authors.lastname: Liu
mesh_terms: D000818:Animals; D002685:Chiroptera / Q000033:anatomy & histology / Q000502:physiology*; D005426:Flight, Animal / Q000502:physiology*; D008954:Models, Biological; D014921:Wings, Animal / Q000033:anatomy & histology / Q000502:physiology*
keywords: bat flight; dynamically changing wingspan; flapping flight; unsteady aerodynamics