Abstract
AbstractFlow control over a NACA 0012 airfoil is carried out using a dielectric barrier discharge (DBD) plasma actuator at the Reynolds number of 20 000. Here, the plasma actuator is placed over the pressure (lower) side of the airfoil near the trailing edge, which produces a wall jet against the free stream. This reverse flow creates a quasi-steady recirculation region, reducing the velocity over the pressure side of the airfoil. On the other hand, the air over the suction (upper) side of the airfoil is drawn by the recirculation, increasing its velocity. Measured phase-averaged vorticity and velocity fields also indicate that the recirculation region created by the plasma actuator over the pressure surface modifies the near-wake dynamics. These flow modifications around the airfoil lead to an increase in the lift coefficient, which is similar to the effect of a mechanical Gurney flap. This configuration of DBD plasma actuators, which is investigated for the first time in this study, is therefore called a virtual Gurney flap. The purpose of this investigation is to understand the mechanism of lift enhancement by virtual Gurney flaps by carefully studying the global flow behaviour over the airfoil. First, the recirculation region draws the air from the suction surface around the trailing edge. The upper shear layer then interacts with the opposite-signed shear layer from the pressure surface, creating a stronger vortex shedding from the airfoil. Secondly, the recirculation region created by a DBD plasma actuator over the pressure surface displaces the positive shear layer away from the airfoil, thereby shifting the near-wake region downwards. The virtual Gurney flap also changes the dynamics of laminar separation bubbles and associated vortical structures by accelerating laminar-to-turbulent transition through the Kelvin–Helmholtz instability mechanism. In particular, the separation point and the start of transition are advanced. The reattachment point also moves upstream with plasma control, although it is slightly delayed at a large angle of attack.
Highlights
Low-Reynolds-number aerodynamics has attracted much interest recently with the deployment of micro air vehicles (MAVs) and small unmanned aerial vehicles (UAVs) in a variety of commercial and military missions (Mueller & Delaurier 2003)
Laminar separation bubbles A pioneering study of separation bubbles over a flat plate under an adverse pressure gradient was conducted by Gaster (1967), who indicated that the structure of the bubble depended on the Reynolds number of the separating boundary layer and a parameter based on the pressure rise over the region occupied by the bubble
Flow control over a NACA 0012 airfoil is carried out using a dielectric barrier discharge (DBD) plasma actuator at a Reynolds number of 20 000
Summary
Low-Reynolds-number aerodynamics has attracted much interest recently with the deployment of micro air vehicles (MAVs) and small unmanned aerial vehicles (UAVs) in a variety of commercial and military missions (Mueller & Delaurier 2003). Without DBD plasma actuation, flow over the suction (upper) surface is fully attached at small angles of attack up to α = 2◦ (figure 6a,c), while it starts to separate near the trailing edge at α = 4◦, forming a small separation region there (figure 6e). The recirculation region stretches downstream beyond the trailing edge, effectively extending the airfoil chord length This is similar to the flow field created by the mechanical Gurney flap (see figures 1 and 8c), only a single recirculation region is seen with plasma control as compared to two separate recirculation regions (one upstream of the flap and other downstream of it) with the Gurney flap. A quasi-steady recirculation region appears near the plasma actuator over the pressure (lower) side of the airfoil near the trailing edge (figure 10a,c,e,g) This draws the air from the suction (upper) surface, nearly eliminating the trailing-edge flow separation. The recirculation region formed by the plasma control shows the quasi-steady characteristics at other angles of attack (not shown here)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
