Information Technology Journal1812-56381812-5646Asian Network for Scientific Information10.3923/itj.2011.748.758XingweiZhangChaoyingZhou42011104The aim of this study is to investigate the influence of nonsymmetrical up-down plunging motion of a forward flight airfoil on its aerodynamic characteristics. Numerical simulations are carried out by using the finite volume method to solve the two-dimensional time-dependent incompressible Navier-Stokes equations. To study the influence of an oblique attack angle, the attack angle is selected from -5 to 10 with an increase of 2.5. For each attack angle, seven nonsymmetrical plunging models are examined. The vortex patterns in the wake of the airfoil corresponding to each case are also analyzed and two types of vortex formation are observed where one has two vortices shed in each plunging cycle and the other has four. The vortex pattern in the wake and the moving direction of the vortices are found to be predominantly determined by the plunging motion with different duration time ratio if the frequency and the amplitude of the plunging motion are fixed. It is found that the nonsymmetrical plunging motion alters the time of flow separation at the leading edge compared to the symmetrical one, which may result in higher propulsions. The moving direction of the vortices is also effected by the attack angle of the wing and the variation in the moving direction of the vortices can cause significant changes in propulsion and lift. The present work confirms that both the propulsive and lifting performance of an airfoil can be improved by a nonsymmetrical plunging motion.]]>Dudley, R. and C.P. Ellington,1990Ennos, A.R.,1989Elhadi, E.E., L. Xiaosong and W. Keqi,2002Issa, R.I., 1985Issa, R.I., B. Ahmadi-Befrui, K.R. Beshay and A.D. Gosman, 1991Lai, J.C.S. and M.F. Platzer,1999Lewin, G.C. and H. Haj-Hariri,2003Leonard, B.P.,1979Lesoinne, M. and C. Farhat,1996Menter, F.R.,1993Miao, J.M. and M.H. Ho,2006Norberg, U.M.L. and Y. Winter,2006Glossophaga soricina, flying at different flight speeds and Strouhal numbers.]]>Park, H.C., S.Y. Lee, S.M. Lim, S.K. Lee, K.J. Yoon and N.S. Goo,2004Rhie, C.M. and W.L. Chow,1983Schilstra, C. and J.H. Hateren,1999Schouveiler, L., F.S. Hover and M.S. Triantafyllou,2005Tobalske, B. and K. Dial,1996Tian, X., J. Iriarte-Diaz, K. Middleton, R. Galvao and E. Israeli et al.,2006Tuncer, I.H. and M.F. Platzer,1996Tuncer, I.H. and M. Kaya,2003Von Karman, T. and J.M. Burgers,1935Versteeg, H. and W. Malalasekera,1995Weis-Fogh, T.,1956Willmott, A.P. and C.P. Ellington,1997Zarnack, W.,1988Zhu, B.L., T.H. Xiao, H.S. Ang and X.C. Zhou,2008