Assessment of Taylor's hypothesis in the presence of mean shear using multi-camera particle image velocimetry

To quantify the validity of Taylor's hypothesis and its effects on estimates of coherent motions in flows with mean shear, experiments were performed in streamwise-wall-normal planes in a turbulent open channel flow over a smooth wall at two conditions (Re_τ=500, 1000). Time-resolved particle image velocimetry measurements were obtained with multiple cameras covering a long streamwise field of view of 12 water depths. This streamwise extent enabled visualization of long streamwise structures in the flow and facilitated the investigation of Taylor's hypothesis. By taking the local mean velocity and global convection velocity (estimated by space-time correlation) as the convection velocity for Taylor's hypothesis, two kinds of reconstructed velocity fields can be obtained and compared with real spatial velocity fields. Results of individual fields and correlation analysis will be presented and discussed including correlation coefficients and scale estimation of coherent motions.