  The separated flow downstream a backward-facing step is controlled using
visual information for feedback. This is done when looking at the flow from two
vantage points. Flow velocity fields are computed in real-time and used to
yield inputs to a control loop. This approach to flow control is shown to be
able to control the detached flow in the same way as has been done before by
using the area of the recirculation region downstream the step as input for a
gradient descent optimization scheme. Visual feedback using real-time
computations of 2D velocity fields also allows for novel inputs to the feedback
scheme. As a proof of concept, the spatially averaged value of the swirling
strength is successfully used as input for an automatically tuned PID
controller.
