Numerically computed spectra and pseudospectra are presented for the linear
operator that governs the temporal evolution of infinitesimal perturbation
s of laminar how in an infinite circular pipe at Reynolds numbers 1000, 300
0 and 10 000. The spectra lie strictly inside the stable complex half-plane
, but the pseudospectra protrude significantly into the unstable half-plane
, reflecting the large linear transient growth that certain perturbations m
ay excite. (C) 1999 Elsevier Science S.A. All rights reserved.