Tracking Stall Cell Dynamics at High Reynolds Numbers

The spanwise organization of the flow over a thick airfoil is investigated using surface pressure measurements for a range of angles of attack around maximum lift and high Reynolds numbers [Formula: see text]. Locally strong pressure fluctuations, which are not detected in the global lift coefficient, are shown to be associated with the presence of a stall cell. The stall cell width is of the order of the chord length and increases linearly with the angle of attack, with a weak dependence on the Reynolds number [Formula: see text]. Its dynamics at Reynolds numbers larger than [Formula: see text] is dominated by a coherent motion in the spanwise direction with a characteristic velocity of order 0.1 U. The motion can be decomposed into a large-scale, low-frequency sweep with a Strouhal number [Formula: see text] combined with faster, smaller-scale oscillations. The coherence of the stall cell makes it possible to track global dynamics from local measurements.