High-speed scanning stereoscopic PIV for 3D vorticity measurement in liquids

A scanning stereo particle image velocimetry (SSPIV) system was developed to measure the three-dimensional (3D) distribution of three-component (3C) velocity in a turbulent round jet. A laser light sheet produced with a high-repetition-rate pulsed Nd:YLF laser was scanned by an optical scanner in a direction normal to the sheet. Two high-speed mega-pixel resolution C-MOS cameras captured the particle images illuminated by the light sheet, and the stereoscopic PIV method was adopted to acquire the 3D-3C velocity distribution of turbulent water flow. A water jet formed by a round nozzle with an exit diameter of D = 5 mm was diagnosed by the current technique. The jet Reynolds number was set at Re ≈ 1000, and the streamwise location of the measurement was fixed at approximately x = 45D. A measurement volume (~100 × 100 × 100 mm3) containing 50 velocity planes was scanned in 0.22 s, which was sufficiently short to capture the instantaneous vortical structures. The residue of the continuity equation (divergence) was approximately 7% of rms vorticity on the centreline of the jet. The iso-vorticity surfaces clearly depict vortical structures in the jet shear layer