Unsteady boundary-layer separation at finite and infinite Reynolds numbers

Abstract eng:
Unsteady boundary-layer separation in the limit as Reynolds number goes to infinity is marked by the onset of the Van Dommelen singularity, which signals a sudden, small-scale eruption of vorticity from the boundary layer. A more complete and comprehensive picture of the unsteady separation process has been sought for some time, including how the limiting process based on asymptotic methods is adjusted for finite Reynolds numbers of practical interest. Here, an alternative mechanism is described that also leads to an ejection of near-wall vorticity, i.e. unsteady separation. It is predicated on the splitting of a recirculation region or vortex within the boundary layer owing to the Vortex-Shedding Mechanism (VSM). However, it is not found to be permissible in the boundary-layer limit. Therefore, it is an alternative to the Van Dommelen singularity-based unsteady separation mechanism that may occur at finite Reynolds numbers.

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