  We propose to combine the active vortex generators with the particle image
velocimetry (PIV) measurements and post-processing streamwise vortex
characterization algorithms into a feedback based closed-loop control system
for wind turbine applications. We develop two vortex identification and
characterization methods that use PIV realizations for the purpose of a
real-time (online or on-the-fly) feedback-based control. Both methods can
extract centers and strengths of streamwise vortices generated behind active
vortex generators in a turbulent boundary layer flow, and we show how to
integrate those in a closed-loop control strategy. For demonstration purposes
we use stereoscopic PIV measurements at the wind tunnel facility obtained in
the transverse-wall-normal plane behind active vortex generators. A robust
algorithm is using the $Q$-criteria and the integration of vorticity of each
extracted vortex. Results show that a moving window average of a small number
of instantaneous fields is nevertheless needed for increased robustness. The
robust method requires the full field PIV computation followed by spatial
derivatives calculations. A faster method is developed, which, using only
horizontal lines of vertical velocity, has a high potential to significantly
cut down the computational effort relative to the robust method. We compare the
two methods and discuss their shortcomings and the potential for the real-time,
online, closed-loop control of turbulent boundary layers of the wind turbine
blades.
