Sources of Error in Eigenvalue Spectra for Pipe-Poiseuille Flows

An operational Chebyshev Tau approach was used to establish temporal eigenvalue stability spectra for pipe-Poiseuille flows, using the Sexl equation which was transformed to remove the singularity at the origin. Substantial deviations were noted between the long-standing results of Davey and Drazin (1969) which are scattered and display branching patterns, and those of the present work which manifest a more orderly progression of the stable high-order eigenvalues. Formal distinctions are made between errors arising from round-off, basis truncation, and poor choice of basis function: the inaccuracies in Davey and Drazin’s data are thought to have arisen from the latter two effects.