title: Saffman-Taylor Instability and the Inner Splitting Mechanism.
abstract: For viscously unstable, miscible Hele-Shaw displacements, we investigate the origin of the streamwise vorticity shown to be responsible for the inner splitting mechanism by Oliveira and Meiburg [J. Fluid Mech. 687 431 (2011)JFLSA70022-112010.1017/jfm.2011.367]. Towards this end, we compare 3D Navier-Stokes simulation results for neutrally buoyant, viscously unstable displacements and gravitationally unstable, constant viscosity ones. Only the former exhibit the generation of streamwise vorticity. The simulation results show that it is caused by the lateral displacement of the more viscous fluid by the less viscous one, with the variable viscosity terms playing a dominant role.
authors.affiliation: Department of Mechanical Engineering, Pontifícia Universidade Católica, Rio de Janeiro, Rio de Janeiro 22451-900, Brazil.
authors.forename: Rafael M
authors.initials: RM
authors.lastname: Oliveira
authors.affiliation: Department of Mechanical Engineering, University of California at Santa Barbara, Santa Barbara, California 93106, USA.
authors.forename: Eckart
authors.initials: E
authors.lastname: Meiburg