Observations regarding ‘‘Coherence and chaos in a model of turbulent boundary layer’’ by X. Zhou and L. Sirovich [Phys. Fluids A 4, 2855 (1992)]

In the following, the present authors comment on a paper by Zhou and Sirovich (ZS) [Phys. Fluids A 4, 2855 (1992)] which contained a critical appraisal of the models developed by Aubry et al. (AHLS) [J. Fluid Mech. 192, 115 (1988)]. It is found that ZS’s suggestion to use ‘‘a full channel interpretation of wall eigenfunctions,’’ thereby avoiding boundary terms, while attractive mathematically, is questionable in fluid mechanical terms. A major point of AHLS’s study was precisely to isolate the wall region and use the boundary terms to investigate the interaction with the outer flow. Also, it is demonstrated that certain instances of ‘‘irregular’’ bursting, as reported by ZS, are probably numerical effects.