ABSTRACT

Coherent streamwise vortical structures inside the centrifugally unstable turbulent boundary layer on the concave (outer) wall of a 90 deg duct are simulated numerically using DES and URANS coupled with an instantaneous random forcing technique to generate inlet boundary conditions. The simulated vortical structures originate approximately halfway through the bend, span the entire concave wall, meander randomly in space, and exhibit intense low-frequency, unsteadiness. Our results show that these structures account for a significant percentage of the total Reynolds stresses inside the concave wall boundary layer but do not result in appreciable spanwise variations of the mean velocity field.