3D scanning PIV applied to an air flow in a motored engine using digital high-speed video

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Abstract
3D scanning particle image velocimetry (SPIV) provides particle images in a large set of parallel light-sheet planes using a rapid scanning light-sheet which samples the flow in depth from which the three-dimensional flow field can be reconstructed in the scanned volume. Together with a digital high-speed video technique and a high-speed rotating drum scanner for 3D beam scanning, first 3D SPIV measurements were carried out in a motored model engine with a transparent cylinder and piston crown. Attention was focused on the generation of small-scale structures during compression strokes. Using a spatial cross-correlation of particle images in the overlapping sheets, the 3D flow field could be recovered from the sheet-wise tomographic recorded flow volume. This demonstrates the potential of 3D SPIV in engine flows since 3D information can be obtained from a single view and therefore the method can be applied in actual research engines already in use without any additional modification. The first results of the feasibility study have shown complex flow at the very end of compression which is characterized here by meandering monopolar and dipolar vortices within the main swirling flow which interact with the centre. It is suggested that the observed vortex splitting and shearing is an important contribution to the creation of turbulence.