*Article* **Computational Study of the Plasma Actuator Flow Control for an Airfoil at Pre-Stall Angles of Attack**

**Takuto Ogawa 1,**<sup>∗</sup> **, Kengo Asada <sup>2</sup> , Makoto Sato <sup>3</sup> , Tomoaki Tatsukawa <sup>2</sup> and Kozo Fujii 2,**<sup>∗</sup>


**Abstract:** Large-eddy simulations of the flows over an NACA0015 airfoil were conducted to investigate a flow control authority of a dielectric barrier discharge plasma actuator at pre-stall angles of attack. The Reynolds number was set to 63,000, and angles of attack were set to 4, 6, 8, and 10 degrees. The plasma actuator was installed at 5% chord length from the airfoil's leading edge. Good flow control authority was confirmed in terms of lift-to-drag ratio increase and drag reduction. These improvements mainly result from the reduction of the pressure drug, which is due to the change in pressure distribution accompanying the movement and shrink of the laminar separation bubble on the airfoil surface. Additionally, although flow control using a burst drive with a nondimensional burst frequency of six improves the lift-to-drag ratio at all angles of attack, the phenomena leading to the improvement differ between near-stall angles (10 and 12 degrees) and the other lower angles. At near-stall angles, the turbulent transition is rapidly promoted by PA, and the flow is reattached. Whereas, at the lower angles, the transport of two-dimensional vortex structures, which maintain their structures up to downstream and suppress the turbulent transition, makes the flow reattachment.

**Citation:** Ogawa, T.; Asada, K.; Sato, M.; Tatsukawa, T.; Fujii, K. Computational Study of the Plasma Actuator Flow Control for an Airfoil at Pre-Stall Angles of Attack. *Appl. Sci.* **2022**, *12*, 9073. https://doi.org/ 10.3390/app12189073

Academic Editors: Josep Maria Bergadà and Gabriel Bugeda Castelltort

Received: 9 August 2022 Accepted: 5 September 2022 Published: 9 September 2022

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**Keywords:** flow control; plasma actuator; airfoil; pre-stall angles; duty cycle; burst; computational fluid dynamics; large eddy simulation
