Publications

Effects of spatial realignment in stereo PIV calibration

Beresh, Steven J.; Smith, Barton L.

Simultaneous stereo PIV measurements of a round free jet were obtained from narrow and wide camera angles while a fifth camera viewed the laser sheet from 90 degrees to determine the two-component velocity field free of errors resulting from stereo calibration. Errors in mean velocities were small, but artificially reduced turbulent stresses were generated when self-calibration was not used, owing to a smearing effect that occurs when the two cameras are inadequately registered to each other. This difficulty worsened with increased laser sheet thickness. Spatial error in the stereo calibration process can artificially displace vector fields from the expected origin, which was detected through comparison to the simultaneous two-component measurement. Although this spatial offset typically is small with respect to statistical properties of a data set, it can be prominent when instantaneous snapshots of the velocity field are examined, particularly where the velocity gradient is momentarily large.