Reattachment

Sometimes, a separated flow will reattach, as illustrated in Fig. 3.4. This is particularly likely to happen if the boundary layer was laminar when it separ­ated. After separation, the layer tends to become turbulent and thus more able to tolerate an adverse pressure gradient.

Between the points of separation and reattachment, a region of recirculating air, known as a separation bubble, is formed, as shown in Fig. 3.4. Many aero­foils show a tendency to produce such a bubble. The lifting properties are not affected, as long as the bubble is sustained.