Kelvin–Helmholtz rollers in turbulent flow over riblets

Abstract

Structures resulting from a Kelvin–Helmholtz instability have been shown to contribute to skin-friction drag in turbulent flow over blade-shaped riblets [4]. Using Direct Numerical Simulation (DNS) data, the present survey of several different riblet shapes reveals that the contribution to wall-shear stress due to the Kelvin–Helmholtz instability depends on riblet shape, in addition to a previously known dependence on riblet size. For a given drag change, sharp triangular and blade riblets promote development of the instability whilst blunt triangular and trapezoidal riblets appear to suppress it.