Boundary Layers

Abstract

The papers presented at the Fourth International Shear Flows Symposium show that the measurement and prediction of the flow in turbulent boundary layers continue to engage the attention of researchers. The practical relevance of the study of boundary layers needs no explanation; at a more basic level many of the fundamental features of turbulent shear flow are conveniently studied in thin shear layers, while the mathematical simplifications of the boundary layer hypothesis have not yet been made unnecessary by advances in numerical methods. It can be argued that the uncertainty involved in the numerical solution of elliptic differential equations for complex flows with recirculation makes the measurements from thin shear layers which can be described by parabolic equations a more reliable test for turbulence model predictions. The acquisition of suitable data for this purpose is one of the two main objectives of experimental turbulence research; the other is still to achieve a more complete understanding of the physical nature of turbulence. The paper by Iritani, Kasagi and Hirata falls into this category. It is concerned with a subject of continuing research interest: the details of turbulence in the immediate vicinity of the wall. A convenient entry to this topic is provided by Hinze in the second edition of his book, which contains a section summarizing the status and observations to 1975. Some of the later work is cited by the present authors who have now made a further contribution by studying the heat transfer mechanism and associated turbulence structure in the near wall region of a boundary layer in a water channel. The results show that the turbulent temperature field near the wall resembles closely the flow structure in the viscous wall region and are compatible with what is known about the streamwise sublayer vortices from previous investigations.