Leading Edge Vortex Induced Effects on Electrical Characteristics of a DBD Plasma Actuator
Creators: name:  J. KISSING 
name:   J. ERHARD 
name:   J. KRIEGSEIS 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: FLOW CONTROL
AEROSPACE

description: Leading edge vortices (LEVs) are the main contributor to augmented lift in unsteady propulsion of low-Re swimmers and flyers and is therefore a flow pattern of particular importance for the maneuverability of micro aerial vehicles (MAV). Since the achieved high amounts of lift impulsively drop after LEV separation (McCroskey, 1982), a vast amount of investigations addresses the characterisation of LEV formation on and detachment from a lifting body (Eldredge and Jones, 2019) as mandatory knowledge for successful LEV-separation control effort. Generally, the breakdown of lift happens to occur either as a result from viscous effects below the LEV or due to fluid recirculation around the trailing edge of the airfoil. Both mechanisms have been found to be characterized (among other means) on the grounds of topological skeleton of the vortical structures on the suction side of the respective airfoil under consideration (Rival et al. ,2014; Widmann and Tropea, 2015). Manipulation of correspondingly identified singular points has, therefore, been hypothesized to be key feature for manipulation of both growth and separation of LEVs. Recently, Kissing et al. (Kissing et al. 2020) have successfully demonstrated the delay of LEV separation from pitching/plunging profiles by means of dielectric barrier discharge (DBD) plasma actuators. Their approach focuses on flow manipulation at topologically critical points, where the flow field is most susceptible with respect to manipulation effects. However, in order to advance beyond the proof-of-concept level towards universal manipulation approaches and efficiency considerations, closed-loop control of LEV manipulation has to be implemented. This requires sensing of topological key characteristics of the flow field to establish a feedback loop, which allows for a specific manipulation at topologically critical locations. Due to highly dynamic motion of the airfoil, representative for biological flight, and electromagnetic induction by the DBD-PA, established sensor principle are not applicable to determine flow topology and the LEV position directly. Additionally, the velocity and pressure induced by the LEV are small compared to the undisturbed flow field on the airfoil (EslamPanah et al., 2015). In this study, first investigations on how the LEV affects electric characteristics of the active plasma actuator are carried out and moreover evaluations on how to use the actuator-performance information for vortex position sensing. This is meant to allow the DBD actuator to be used in an advanced control circuit. Current investigations are based on the hypothesis, that even small changes of the external velocity and/or pressure level interact with the ionic wind, induced by the plasma actuator, which in turn alter its electric key characteristics. Such interactions have been reported previously for high amplitude velocity fluctuations by other studies (Kriegseis et al., 2012; Kriegseis et al., 2014). A DBD-PA applied to a flat plate airfoil, which executes combined pitching and plunging kinematics inside a wind tunnel, is considered to study vortex induced effects on electrical key characteristics of the actuator in three different discharge regimes. Time-resolved 2D2C Particle Image Velocimetry measurements of the flow field are used complementary to extract the LEV center position as well as the flow velocity right above the DBD-PA. It is found that the LEV has a significant influence on electric key characteristics of the actuator in all three discharge regimes. Evolution of the respective electric characteristics are correlated with the LEV induced tangential flow velocity at the plasma actuator location on the unsteady airfoil. Based on the fact, that the induced tangential flow velocity correlates linearly with the distance of the vortex, correlations of the distance of the leading edge vortex and the electric characteristics of the plasma actuator are obtained.