Piezo-stack vortex generators for boundary layer control of a delta wing micro-aerial vehicle Arkadiusz Mystkowski n Faculty of Mechanical Engineering, Bialystok University of Technology, Wiejska 45C, 15-351 Bialystok, Poland article info Article history: Received 23 July 2012 Received in revised form 10 May 2013 Accepted 29 May 2013 Available online 4 July 2013 Keywords: Boundary layer control Flow separation Piezo-stack Vortex generator BULLIT abstract This paper presents an idea for the control of flow separation over solid surfaces by piezo- stack vortex generators. The vortex generators are small vibrating plates attached to the delta wing surface. A model of the micro-aerial vehicle (MAV) controlled by vortex piezo- generators is presented. The vortex generators are applied to produce the appropriate aerodynamical forces and moments controlling the flight of the aircraft. The efficiency of the vortex generators is proved by the wind tunnel test results. The oscillatory added lift and drag coefficients versus angle of attack are presented. The optimal vortex generator amplitude and frequency are investigated. Boundary layer control (BLC) for delta wing micro-aircraft increases the manoeuvrability and performance of the MAV. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction The boundary layer control (BLC) using external periodical excitation was introduced by Schubauer and Skramstad [18]. The principle of the excitation method is to control the flow of the air over a body by imparting controlled periodic perturbations in a laminar boundary layer to trigger a known instability called the Tollmien–Schlichting waves. The boundary layer control means control of its attachment to a solid surface and prevention of flow separation [17]. Turbulent flow is more resistant to separation from a solid surface than laminar flow. Flow separation is usually negative and associated with loss of some performance indicators, i.e. it decreases the lift and increases the drag forces [2,9,22]. The separation of the boundary layer at the top surface of the wings restricts the manoeuvrability of an aircraft. The periodic excitation can be achieved by using many types of mechanical actuators [1,5,14]. The MEMS based actuators are piezoelectric very often [19,21]. In the micro-aerial vehicles, micro-flap vortex generators can be applied to flow control by excitation [6,7,15,16]. The vortex generators work by mixing high energy air from the free stream with the lower energy air from the boundary layer. The micro-aerial vehicles (MAVs) present many difficulties in the testing, control and fabrication processes. The most important include low Reynolds number flows (10 4 –10 5 or lower), low airspeed (10–20 m/s), fluid–structure interactions and small area of the wing [13]. The viscosity forces have a big influence on the low airspeed aerodynamics. Moreover, in the MAVs the interaction between unsteady aerodynamics and structural flexibility is critical [8]. From the control point of view, the unsteady flow effect in the small scale MAVs, very low wing loading and almost nonexistent inertia cause stability and manoeuvreing problems [10–12]. The small oscillating plates, called smart control surfaces, attached to the MAV's wing surface are unable to produce enough dynamic moments to maneuver aircraft in the urban environment. When the MAV Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/ymssp Mechanical Systems and Signal Processing 0888-3270/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ymssp.2013.05.019 n Tel.: +48 857469226; fax: +48 857469210. E-mail address: a.mystkowski@pb.edu.pl Mechanical Systems and Signal Processing 40 (2013) 783–790