Stability of the Rotating-Disk Boundary Layer: Roughness Effects and Beyond
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Results of our computations [1-3] investigating the effects of surface roughness on the stability of the boundary-layer flow over a rotating disk will be summarized. The results reveal stabilising, that is energetically beneficial, effects on the dominant instability mode responsible for transition over rotating disks. This result is qualitatively consistent with the measurements in Ref.  which show drag reduction of up to 15% for disks with roughness patterns similar to those studied computationally in Refs. [1-2]. The agreement suggests that, in the long-term, our computational methods may enable the design of energetically optimized surface roughness for laminar-flow control in the applied context of new drag-reduction techniques in, for instance, aeronautics. Our results [1-3] for rough disks will be briefly compared to corresponding computational data by other authors who studied transition over rotating speed-modulated disks, rotating disks with compliant surfaces and rigid disks spinning in non-Newtonian liquids. The goal of this comparison is to highlight some qualitative similarities of the results for all these different scenarios.