Int. Conf. on Jets, Wakes and Separated Flows, ICJWSF-2008 September 16-19, 2008, Technical University of Berlin, Berlin, Germany 1 TEMPORAL ANALYSIS OF JET AND VORTEX ACTUATOR (JAVA) – INDUCED FLOWS Hasan Gunes *1 , Sertac Cadirci 1 , Franceso Baldani 2 , Bernd Peters 3 , Ulrich Rist 3 1 Department of Mechanical Engineering, Istanbul Technical University, Gumussuyu, 34437 Istanbul, Turkey E-mail * : guneshasa@itu.edu.tr 2 University of Bologna, Forli, Dipartimento di Ingegneria delle Costruzioni Meccaniche, Nucleari, Aeronautiche e di Metallurgia Via Fontanelle 40, 47100 Forli, Italy 3 Institut für Aerodynamik und Gasdynamik, Universität Stuttgart, Pfaffenwaldring 21, D-70550 Stuttgart, Germany ABSTRACT A zero-net-mass flux Jet and Vortex Actuator (JaVA) device for active flow control was investigated in detail experimentally. The JaVA system in this study is derived from the work of Lachowicz et al., 1999. However, unlike there, we built a larger JaVA system and tested it in still water at much lower frequencies of order one. While attesting the same governing JaVA parameters (e.g, Reynolds number, scaled amplitude), such low-frequency values would allow us real-time observations with naked eye. The typical flow regimes induced by the JaVA system include angled jet, vertical jet, wall jet and vortex flows, as reported by Lachowicz et al., 1999. In this paper, we investigate the detailed quantitative temporal behaviour of basic JaVA-induced flow types utilizing the optical flow concept based on an image-gradient processing method. The temporal dynamics of instantaneous velocity fields obtained via optical flow are then investigated using Fourier analysis. 1 INTRODUCTION This paper focuses on investigation of the dynamics of a zero-net-mass-flux actuator for active control of boundary layers and flow separation, which is characterized by a high flexibility of operation. This active flow control device, called the Jet and Vortex Actuator, or simply JaVA, is expected to achieve control of drag in boundary layers or re-energize laminar and turbulent boundary layers to resist to separation. For improving aircraft aerodynamic performance, existing flow control strategies have been mostly based on passive control. Passive control means that fixed devices/elements are used to control/intervene the flow. For example, fixed vortex generators often can be used for passive flow control (Gad-el-Hak, 2006). Conventional passive vortex generators are simple and usually effective to overcome existing flow separation problems (Taylor, 1948). These devices are low cost in manufacture, but they have two significant disadvantages: first, passive flow control devices cannot be optimized for multiple flight conditions (e.g., landing, take-off and manoeuvering), and second, they add an extra drag in steady cruise conditions in which they are no longer needed (Lachowicz et al., 1999). Active flow control, on the other hand, can defeat these disadvantages and optimize overall performance of the flight. Specifically, the jet and vortex actuator (JaVA) would add no or only negligible drag when the system is not actuated and it does not need any external fluid because it is a zero-net-mass flux system. The JaVA enables to achieve different flow regimes such as angled, vertical and wall jets and vortex flows since it can operate over a range of amplitudes and frequencies. This kind of active flow control includes vortex generation and discrete jet injection for streamwise vortex generation (Wallis and Stuart, 1951). On the other hand, wall jets have been shown to be capable of a straightforward flow separation control which is applied to military fighters (Gratzer, 1971). In another research, it has been shown that active flow control via vorticity generation enhanced boundary-layer momentum transport and thus suppressed stall for both compressible and incompressible flows (Mc Manus et al., 1997). With the full understanding and interaction with boundary layers, a successful application of a JaVA system may lead to efficient flight control systems, thus manoeuvrability, stability and longer aircraft range can be possible at a reduced cost. 2 THE JAVA SYSTEM Our JaVA body is a Plexiglas cavity with an actuator plate which is moving up and down like a piston and driven by an eccentric tappet like the cam shaft of a car engine. The frequency and the amplitude of the actuator can be changed