Experimental validation of sensor placement for control of a D-shaped cylinder wake

The effectiveness of a sensor configuration, based on body mounted sensors, for feedback flow control of a D-shaped cylinder wake is investigated experimentally. The research is aimed at suppressing unsteady loads resulting from the von Kármán vortex shedding in the wake of bluff bodies at a Reynolds number range of 100-1000. A low-dimensional Proper Orthogonal Decomposition (POD) procedure was applied to the stream-wise and cross-stream velocities in the near wake field obtained using Particle Image Velocimetry (PIV) with steady state vortex shedding. The data was collected from the unforced condition, which served as a baseline, as well as during influence of forcing but within the "lock-in" region. The design of sensor number and placement was based on data from a laminar direct numerical simulation of the Navier Stokes equations. A Linear Stochastic Estimator (LSE) was employed to map the surface mounted sensor signals to the temporal coefficients of the reduced order model of the wake flow field in order to provide accurate yet compact estimates of the low-dimensional states. For a three sensor configuration, results show that the root mean square estimation error of the first two cross-stream modes is within 20 - 40% of the PIV generated POD time coefficients. This level of error is acceptable for a moderately robust controller required to close the loop, based on previous investigation.