Absolute and convective instabilities in separation bubbles

At a sufficiently high Reynolds number small separation bubbles, as for example at the leading-edge of an aerofoil, are characterised by laminar flow separation and turbulent reattachment. The transition to turbulence in the separated-flow region through the introduction of a disturbance at the boundary, localised in time and space, is examined. It is found that transition to turbulence is promoted by rapidly growing convective instabilities, and not an absolute instability at the point of application of the disturbance.