The Role of Frequency and Phase Difference Between the Flow and the Actuation Signal of a Tangential Synthetic Jet on Dynamic Stall Flow Control

In this paper, we have studied the active flow control (AFC) of a pitching airfoil by means of a tangential synthetic jet actuator (SJA) using computational fluid dynamics. The airfoil was NACA0012 which pitched about its quarter-chord with a sinusoidal motion at Reynolds number of 1 × 10⁶. Several high-frequency actuations (HFAs), in the order of nominal shedding frequency of static condition; $Fj+=$ 1.0, 2.0, and 3.0, one low frequency actuation $Fj+=$ 0.2, and one very low frequency actuation $Fj+=$ 0.047 where the frequency of the SJA matched that of the pitching motion of the airfoil were considered. The resulting lift and drag diagrams were compared with each other, as well as with the uncontrolled case and the continuous jet. It was found that oscillations in drag and lift hysteresis curves with the associated local minima and maxima were connected to the ingestion/expulsion cycles of the SJA. At the very low-frequency actuation (LFA), which synched the frequency of the SJA to the frequency of the pitching motion, several phase differences (⁠$Δφ$⁠) between SJA and pitching motion were studied. Our numerical results have demonstrated that the synched frequency case with $Δφ=180deg$ was far more superior to all other controlled cases studied here and the continued jet of our previous work. This condition even performed better than high frequency actuation with higher jet velocity ratios.