Dimples as a drag reduction technique: a preliminary DNS study

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Matteo Silvani

The present work aims at paving the way to future studies relating or not the occurrence of drag reduction within the technique of dimpled surfaces. Dimples immersed in a turbulent boundary layer still represent one of the newest and more debated passive flow control techniques. Here are presented the major research contributions, among which, one in particular is selected to be replicated with an innovative immersed boundary direct numerical simulation (DNS) code suited for studying the turbulent channel flow problem with the ability of modeling virtually any kind of wall surface. The selected dimple geometry is analyzed into a turbulent flow regime. The code is manipulated to suit the model of the dimple, which is redefined in an accurate manner starting from the current available literature, which often presents unclear or in disagreement results.

The selected dimple geometry proves to be one of the most exploited for its analytical mathematical definition and the possibility of being constructed and implemented. The hope for such a passive flow control device to positively affect drag is still out there, or at least the hope to clarify its behaviour, and with this work may be a little bit closer, especially for those who would like to start from this dimple geometry and push forward the research with more powerful numerical tools, higher Reynolds number closer to real possible applications and a parametric study which takes into account a variation of the shape or the mutual disposition of the dimples on the surface. The adopted numerical code proves itself to be a useful and powerful tool to search for new scientific evidence even within the case of dimples.