Turbulent Boundary Layer

Abstract

INTRODUCTION In recent years there is a renewed interest in turbulent boundary layers. On one hand there is an insistent demand for reliable prediction methods to calculate the streamwise development of the gross properties of the bound­ ary layer; so, in addition to the calculation of lumped parameters such as the displacement thickness, the skin-friction coefficient, etc., the prediction of mean velocity and shear-stress distributions across the layer is also re­ quired. On the other hand, there is continuing research interest aimed toward finding an understanding of turbulent shear flows of which the boundary layer is probably the most interesting example. Both theoretical and experimental work on the structure of turbulence in boundary layers continues to be active as shown by the numerous research papers published. The serious interest in turbulent boundary layers has been evidenced by the fact that large meetings were dedicated to the subject. In 1966 an International Symposium on Boundary Layers and Turbulence was held in Kyoto (1). Two years later, in 1968, a different, new type of meeting took place: the Stanford Conference on Computation of Turbulent Boundary Layers (2). In the same year the NASA Symposium on Compressible Turbulent Boundary Layers was organized at Langley Research Center in Virginia (3). The two meetings in 1968 served largely pragmatic interests but, in the last years, more basic work was also reported with the aim of finding an un­ derstanding of the turbulent structure within boundary layers and in related shear flows. A review of turbulent shear flows given by Phillips (4) dealt with the more general aspects of the problem of maintaining the shear stress by the turbulent velocity fluctuations; consequently the present author has chosen to emphasize the boundary layer in preference to other types of shear flow. In experimental turbulence research, the general availability of hot-wire anemometry on a routine basis is now taken for granted. Furthermore, addi­ tional measuring techniques have opened up new vistas in deciphering the intricacies of the turbulent flow structure. These new techniques may in­ clude, among others, novel visualization methods that even permit quantita­ tive analysis, or alternately advanced signal processing schemes for hot-wire