Experiments on the behaviour of an axisymmetric turbulent boundary layer with a sudden circumferential strain

Abstract

Mean velocity and mean turbulent field measurements are performed for the case of a three-dimensional turbulent boundary layer on an axially rotated cylinder. The cylinder model consists of two parts: a stationary section followed by a spinning afterbody. Techniques of hot-wire anemometry are employed, which yield complete mean velocity and turbulence measurements in skewed flows. The general behaviour of the three-dimensional boundary layer is first discussed: two asymptotic layers analogous to the two-dimensional wall and defect layers are observed; they are shown to evolve from the equations of mean motion. The hypothesis of scalar eddy viscosity is investigated in the light of these results. Using conventional length scale assumptions together with the Reynolds stress tensor equations, a prediction of curvature effects in the law of the wall region is developed; a result in the present case is a smaller slope of the semi-logarithmic portion of the law of the wall, No assumptions over and above those necessary for plane, two-dimensional flow are required for this analysis. The geometry of the model is such that a rapid change in mean rate of strain occurs along the streamlines. From the history of the components of the tensor, it is possible to draw some fundamental conclusions concerning the dynamics of the energy dissipation, diffusion and redistribution processes.