a1 Área de Mecánica de Fluidos, Universidad de Jaén, Campus de las Lagunillas, 23071 Jaén, Spain
a2 Manchester Centre for Nonlinear Dynamics, The University of Manchester, Manchester M13 9PL, UK
Results of three-dimensional numerical simulations of the flow through a sudden expansion in a pipe are presented. The axisymmetric state is known to be stable over the range of Reynolds numbers studied, but recent experimental results suggest bifurcation phenomena. A resolution of this dichotomy between calculation and experiment is provided using imperfections to promote the nonlinear development of asymmetric steady states. These lose stability to disordered motion and the boundary between the steady and time-dependent flows has been established over a range of parameters. Moreover, disordered flows are found to co-exist with the axisymmetric regime when the disturbance is removed from the flow. Hence we provide direct numerical evidence for multiplicity of solutions for the axisymmetric expansion problem, which may have relevance to pipe flows.
(Received June 13 2011)
(Reviewed October 15 2011)
(Accepted October 20 2011)
(Online publication December 12 2011)