Synchronized force and particle image velocimetry measurements on a NACA 0015 in poststall under control of time periodic electromagnetic forcing

The paper shows the results of an experimental flow control investigation using periodic actuation by streamwise Lorentz forces at the leading edge of a NACA 0015 profile. Synchronized measurements of force and time resolved particle image velocimetry were performed in a sodium hydroxide channel for Reynolds numbers of Re=0.5×105 and 105. A wavelet algorithm was used to detect vortical structures and reveals the relation between these large scale structures and the observed lift and drag forces. Complementary information on vortical structures was gained by vorticity based proper orthogonal decomposition of the data. In order to minimize the energetic effort of the flow actuation, the investigation focuses on small momentum coefficients. For small angles of attack, a complete reattachment of the flow can be established by the actuation, whereas for large angles of attack, the interaction of vortical structures becomes more prominent. This paper discusses the effects of excitation frequency and wave form for two qualitatively different flow regimes. It is found that for larger angles of attack, the optimal excitation frequency in terms of lift gain is similar to the dominant frequency of the lift fluctuations observed for the unforced flow. This frequency is determined by the wake.