Improved Aerodynamic Characterization of Regular Three-Dimensional Roughness

Surface roughness can seriously degrade the lift-and-drag performance of airfoils, wings, and turbomachinery blading. The ability to predict its effects is therefore important, and this generally requires computation of the viscous flow over the body. The two most common approaches for the viscouscomputations are to use wall functions,i.e., the law of the wall with modifications to represent roughness effects, for the near-wall flow or to integrate the equations of motion from the wall using a turbulence model that includes a correlation for roughness effects. In both the wall-function and the turbulence -model approaches, it is necessary to characterize the actual roughness either in terms of its standard-sand height k s or, equivalently, in terms of the shift C that it produces in the law-of-the-wall intercept. We adress this question by examining the correlation between the geometry of regular arrays of three-dimensional roughness elements and the shift C