Experimental evidence for the existence of the ‘mesolayer’ in turbulent systems

The paper is a study of experimental data in the light of new theories of turbulence recently developed by the first author for a number of problems including flow in a pipe, boundary layer at zero incidence, atmospheric boundary layer, turbulent convection and distribution of energy in wavenumber space in decaying, isotropic turbulence. In each of these, a basic element is a ‘mesolayer’ or ‘mesoregion’ in physical space or wavenumber space which is absent in earlier theories and which intrudes between the inner and outer regions preventing the overlap assumed in the derivation of the classical results, e.g. the logarithmic profile in shear flow. The new and old theories differ both in principle and in the final results: the new ideas replace rather than modify or extend the older ones. The main purpose of this paper is to bring together accumulated evidence concerning the mesolayer theories. We believe that this evidence provides overwhelming support for the existence of the mesolayer and for its pervasive importance in problems of turbulence. Editorial footnote. Although the referees were not persuaded that the claims for the ‘new theories of turbulence’, made by the authors in the abstract and elsewhere in this paper, are justified, we think that publication in the Journal may serve a useful purpose. The authors have assembled a large body of data for various turbulent flow systems. These data should enable readers to test different aspects of the ‘classical’ and ‘new’ theories for themselves and should stimulate thought about the foundations of the classical ideas and about extensions of these ideas, as well as about the validity of the new theories.