Electromagnetic excitation of separated flows: Coherent structures and mean flow features

Flow separation and its control is a persistent topic of fluid dynamic research with large technological importance. Since the early 1990s, separation control by periodic addition of momentum, now commonly termed “active flow control”, has been a subject of intense research. Its main advantage compared to steady actuation is that a control goal, e.g. a specific lift increase, can typically be attained by orders of magnitude smaller momentum input . The significant actuation parameters are mainly the time averaged momentum input and the normalized excitation frequency.
The present lectures discusses the applicability of electromagnetic forces to control separated flows. Simultaneous time resolved force measurements and flow fields obtained by Particle Image Velocimetry on a NACA 0015 are presented. The effects of momentum coefficient, exciatation frequency and -wave-form on the coherent structures and the resulting mean flow are discussed.