Spectra and pseudospectra for pipe Poiseuille flow

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.