Effect of a short region of high convex curvature on heat transfer through a turbulent boundary layer

Abstract

Extensive surface and single-point turbulence measurements have been made in the turbulent boundary layer on a heated flat surface downstream of a short convex bend with a turning angle of 30°. The purposes of the work were to investigate the response of the temperature boundary layer to an “impulse” of curvature, to discover whether this differs from the response of the velocity boundary layer, and to provide measurements of both in enough detail to be use to turbulence modelers. One effect of the attenuation of turbulence in the bend is to reduce the Stanton number of surface heat transfer to 82% of the value it would otherwise have had in flat-wall flow. A substantially larger fall in the skin-friction coefficient is attributable to pressure-gradient effects. The results can be interpreted in the light of a postulated damped oscillatory response to the perturbation. In these terms it is found that the period and amplitude of the temperature flux and variance are greater than the period and amplitude of the shear stress and intensity. The results do not support the view that heat is more sensitive than momntum transfer to curvature effects, but there is some indication that the effects of very strong curvature may differ quantitatively from the effects of prolonged mild curvature observed in earlier experiments.