Flow control over an airfoil using virtual Gurney flaps

Abstract

Flow 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.

Numerical Assessment of Virtual Control Surfaces for Load Alleviation on Compressor Blades

“…[16][17][18][19][20], where the same effects were obtained with a mechanical L-tab deflected downward or upward, installed on a helicopter blade section. Additionally, the computed flow fields are qualitatively consistent with the Particle Image Velocimetry measurements of Feng et al [21] on a low-speed fixed wing section with PS plasma actuation opposite to the freestream direction. Figure 10 shows an histogram of the aerodynamic loads, computed on the clean, PS-and SS-actuated configurations, at angles of attack ranging from 0 to 12 degrees.…”

“…Specifically, plasma actuation is meant to develop vortical structures and recirculating flow areas similar to those generated by mechanical control surfaces (see, for instance, Ref. [21]). Plasma actuators are thought to be located on the pressure and on the suction side (PS and SS, respectively) of the three central blades in the targeted cascade.…”

Тягово-Энергетические Характеристики Плазменных Актуаторов При Различных Давлениях

“…47220.17562 На данный момент существует множество работ, посвященных исследованию диэлектрического барьерного разряда (ДБР) и создаваемых им струй [1][2][3]. В частности, эти работы ориентированы на использование ДБР актуаторов в качестве элементов управления потоком вокруг крыльев летательного аппарата [4,5]. В таком качестве актуаторы эффективны при небольших скоростях полета (до 25 m/s) и числе Рейнольдса Re ∼ 10 4 .…”

Linear feedback stabilization of point-vortex equilibria near a Kasper wing

“…For instance, synthetic jet actuators are commonly used to perform such flow control over aerofoils (Smith et al, 1998). Another approach is to use some form of actuation to "simulate" a passive control, for example, by using plasma actuators to imitate Gurney flaps (Feng et al, 2015).…”