Measurements with a flow direction boundary-layer probe in a two-dimensional laminar separation bubble

Measurements with a directional sensitive hot-wire probe have been carried out in a two-dimensional laminar separation bubble caused by an adverse pre ssure gradient. The probe has three parallel, in plane wires and can be tra versed in the boundary layer in all spatial directions. The central wire, o perated as a conventional hot-wire in CTA mode, and two surrounding resista nce wires measure the instantaneous magnitude and direction of the flow, re spectively. The probe is calibrated and operated in a similar way as a sing le hot-wire probe for boundary layer measurements. The frequency response i s high enough for measurements of naturally occurring instability waves in the bubble. The flow direction intermittency was measured inside the bubble and regions with reversed flow were mapped out. Prior to reattachment peri odical oscillations of the flow direction are found associated with sheddin g of vortical structures from the bubble.