Tomographic 3D-PIV and Applications

Abstract

Tomographic PIV is a newly developed 3D (volumetric) flow field measurement technique, which provides the instantaneous 3C-velocity field within a three-dimensional volume. The experimental apparatus is similar to 3D-PTV using typically four cameras recording simultaneously the illuminated volume from different viewing directions. The particle light distribution is back-projected from the views through a tomographic algorithm (MART) and the volume is discretized into into small voxels where the intensity is reconstructed. A 3D-cross-correlation between interrogation volumes of e.g. 48x48x48 voxels evaluates the 3D-vector field. Advanced robust iterative schemes with deformed interrogation volumes have been implemented. The technique has been applied to a flow behind a circular cylinder in air at Re = 2700 and in water for Re = 360 to 2000. The number of computed vectors has been between 100.000 and 300.000 vectors depending on the size of the sensors used for the recording. The measurement precision was estimated at about 0.05 px. Such experiments allowed to directly inspect the three-dimensional structure of cylinder wakes revealing the secondary flow features like pairs of ‘finger’ vortices. A high repetition rate system allows to perform time-resolved 3D-PIV (4D) measurements of a turbulent spot in a laminar boundary layer with a resolution of 0.4 ms showing the development of Q2-events