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Turbulent separation upstream of a forward-facing step


D. Pearson, P.J. Goulart, B. Ganapathisubramani

Journal of Fluid Mechanics, vol. 724, pp. 284--304

The turbulent flow over a forward-facing step is studied using two-dimensional time-resolved Particle Image Velocimetry. The structure and behaviour of the separation region in front of the step is investigated using conditional averages based on the area of reverse flow present. The relation between the upstream point of separation and the two-dimensional shape of the separated flow is presented. It is shown that the separation region is of `open' form for approximately half the time. When of `closed' form, the separation region can become unstable and extend over the top of the step. The separation region is shown to grow simultaneously in both the wall-normal and streamwise directions, to a point where the maximum upstream extent of the separation point is limited by the accompanying transfer of mass over the step corner. The conditional averages are traced backwards in time to identify the average behaviour of the boundary layer leading up to such events. It is shown that large separation events are preceded by the convection of low velocity regions from upstream, resulting in a three-dimensional interaction with the separation region at the step face. The size and shape of the low velocity regions, and the timescale at which they interact with the separation region, is shown to be consistent with that of large structures in the outer boundary layer observed in the literature. Instances of a highly suppressed separation region are accompanied by a steady increase in velocity of the upstream boundary layer.

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% Autogenerated BibTeX entry
@Article { PeaGou:2013:IFA_4078,
    author={D. Pearson and P.J. Goulart and B. Ganapathisubramani},
    title={{Turbulent separation upstream of a forward-facing step}},
    journal={Journal of Fluid Mechanics},
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