a1 Department of Mechanical and Aerospace Engineering, Monash University, Victoria 3800, Australia
a2 Department of Aeronautics, Imperial College London, SW7 2AZ, UK
a3 Mathematics Institute and Centre for Scientific Computing, University of Warwick, Coventry CV4 7AL, UK
We show that suitable initial disturbances to steady or long-period pulsatile flows in a straight tube with an axisymmetric 75%-occlusion stenosis can produce very large transient energy growths. The global optimal disturbances to an initially axisymmetric state found by linear analyses are three-dimensional wave packets that produce localized sinuous convective instability in extended shear layers. In pulsatile flow, initial conditions that trigger the largest disturbances are either initiated at, or advect to, the separating shear layer at the stenosis in phase with peak systolic flow. Movies are available with the online version of the paper.
(Received November 21 2007)
(Revised April 07 2008)