The effect of a single three-dimensional roughness element on the boundary layer transition
Most studies of TS wave evolution consider a perfectly smooth surface, whereas studies of roughness induced transition consider a perfectly quiet flow. It appears that a combination of these scenarios could better represent a practical situation. This work investigates the effect of a small and medium sized $$ (h/\partial^* < 0.2) $$ roughness on the evolution of a pre-existing T-S wave. A cylindrical element was used as a localized roughness. Several roughness heights were tested experimentally under different sets of flow parameters. The results indicated that under various circumstances the fundamental resonance was the dominant mechanism in the wake of the roughness. A physical model for the prediction of the effect the roughness on a non quiet environement was then proposed and verified.
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