A DNS Study on the Effects of Streamwise Convex Surface Curvature on Coherent Structures in Turbulent Boundary Layers

Direct numerical simulation results are used to establish the effect of streamwise convex surface curvature on the development of turbulent boundary layers, and the effect of such curvature on the forced-convection heat transfer variations observed at certain supercritical thermodynamic states. The results illustrate the stabilizing effects of this flow geometry through modification of the structure and distribution of hairpin-like vortical flow structures in the boundary layer. Specifically, the radial equilibrium mechanism existing on the streamwise convex surface acts to decrease the streamwise spacing of hairpin-like structures within a wave packet and increase the spanwise spacing of the hairpin-like structures in comparison to the behaviour of such structures within the boundary layer on a flat surface. Furthermore, enhancement of convective heat transfer realized at a particular heat flux-to-mass flux ratio with the working fluid at a supercritical thermodynamic state is observed to be reduced by the stabilizing effect of convex surface curvature.