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Unsteady transient phenomena in flow over impulsively started circular cylinder, such as the generation of separation, burst of separation bubble, vortex shedding, etc., are studied from Lagrangian viewpoint. The transient flow is solved numerically by using characteristic-based split scheme with dual time stepping. Then Lagrangian coherent structures (LCSs) are extracted to study the transport and mixing of these transient phenomena. Results show that the variation of drag is closely related to the evolutions of separation bubbles and vortex shedding. The evolutions of the symmetric bubbles in streamwise induce high pressure distribution at rear of cylinder and result in drag reduction of the circular cylinder. As separation bubbles become asymmetric, the transport between separation bubbles and main flow is enhanced and thus can reduce the separation region and suppress flow separation as well. The results also show that the shedding vortices are induced by the transpor between separation bubble and main flow. Compared with streamline patterns, LCSs have huge advantages in describing the dynamic features of the unsteady phenomena.
[1] Gordnier R E 2009 J. Fluid Struct. 25 897
[2] Lei P F, Zhang J Z, Chen J H 2012 Acta Mech. Sin. 44 13 (in Chinese) [雷鹏飞, 张家忠, 陈嘉辉 2012 力学学报 44 13]
[3] Carberry J, Sheridan J 2001 J. Fluid Struct. 15 523
[4] Collins W M, Dennis S C R 1973 J. Fluid Mech. 60 105
[5] Chen Y, Fu S X, Xu Y W, Zhou Q, Fan D X 2013 Acta Phys. Sin. 62 064701 (in Chinese) [陈蓥, 付世晓, 许玉旺, 周青, 范迪夏 2013 62 064701]
[6] Koumoutsakos P, Leonard A 1995 J. Fluid Mech. 296 1
[7] Van Dommelen L L, Cowley S J 1990 J. Fluid Mech. 210 593
[8] Duan J, Wiggins S 1997 Nonlinear Proc. Geoph. 4 125
[9] Haller G, Yuan G 2000 Physica D 147 352
[10] Haller G 2011 Physica D 240 574
[11] Beron-Vera F J, Olascoaga M J, Goni G J 2008 Geophys. Res. Lett. 35 L12603
[12] Lapeyre G 2002 Chaos 12 688
[13] Green M A, Rowley C W, Haller G 2007 J. Fluid Mech. 572 111
[14] Lipinski D, Cardwell B, Mohseni K 2008 J. Phys. A: Math. Theor. 41 344011
[15] Green M A, Rowley C W, Smits A J 2010 Chaos 20 017510
[16] Shadden S C, Lekien F, Marsden J E 2005 Physica D 212 271
[17] Gaitonde A L 1998 Int. J. Numer. Meth. Eng. 41 1153
[18] Nithiarasu P 2003 Int. J. Numer. Meth. Eng. 56 1816
[19] Dupuis A, Chatelain P, Koumoutsakos P 2008 J. Comput. Phys. 227 4486
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[1] Gordnier R E 2009 J. Fluid Struct. 25 897
[2] Lei P F, Zhang J Z, Chen J H 2012 Acta Mech. Sin. 44 13 (in Chinese) [雷鹏飞, 张家忠, 陈嘉辉 2012 力学学报 44 13]
[3] Carberry J, Sheridan J 2001 J. Fluid Struct. 15 523
[4] Collins W M, Dennis S C R 1973 J. Fluid Mech. 60 105
[5] Chen Y, Fu S X, Xu Y W, Zhou Q, Fan D X 2013 Acta Phys. Sin. 62 064701 (in Chinese) [陈蓥, 付世晓, 许玉旺, 周青, 范迪夏 2013 62 064701]
[6] Koumoutsakos P, Leonard A 1995 J. Fluid Mech. 296 1
[7] Van Dommelen L L, Cowley S J 1990 J. Fluid Mech. 210 593
[8] Duan J, Wiggins S 1997 Nonlinear Proc. Geoph. 4 125
[9] Haller G, Yuan G 2000 Physica D 147 352
[10] Haller G 2011 Physica D 240 574
[11] Beron-Vera F J, Olascoaga M J, Goni G J 2008 Geophys. Res. Lett. 35 L12603
[12] Lapeyre G 2002 Chaos 12 688
[13] Green M A, Rowley C W, Haller G 2007 J. Fluid Mech. 572 111
[14] Lipinski D, Cardwell B, Mohseni K 2008 J. Phys. A: Math. Theor. 41 344011
[15] Green M A, Rowley C W, Smits A J 2010 Chaos 20 017510
[16] Shadden S C, Lekien F, Marsden J E 2005 Physica D 212 271
[17] Gaitonde A L 1998 Int. J. Numer. Meth. Eng. 41 1153
[18] Nithiarasu P 2003 Int. J. Numer. Meth. Eng. 56 1816
[19] Dupuis A, Chatelain P, Koumoutsakos P 2008 J. Comput. Phys. 227 4486
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