Abstract
Transonic wind tunnel tests on 2D airfoils with tripped transition and unsteady wall pressure or laser velocimetry measurements show that buffeting appears, at high lift coefficient, like a well-established oscillation of the upperside shock wave and the separated flow which is born at its foot. During cryogenic tests at high Reynolds numbers, the buffeting onset conditions and the nature and the intensity of the phenomenon are not clearly modified, but a specific temperature effect on the oscillation frequency, through sound speed variation, is observed. For free transition tests at low Reynolds number, the boundary layer remains laminar up to the shock and the oscillation does not appear in buffeting conditions, there is only a strong increase of the pressure fluctuation level on the airfoil, without any particular frequency. The characteristics (extent, sensitivity) of the separated flow which is generated by the interaction between shock wave and boundary layer seem to govern these instabilities.
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