Exploration of turbulent swirling flows with high-speed dual-plane stereo-PIV

Turbulent swirling flows are highly three dimensional and spatially developing, including the mean flow, the large coherent structures and small-scale turbulence. Single-plane particle-image-velocimetry (PIV)/planar-laser-induced-fluorescence (PLIF) measurements, commonly used in laboratorial research on turbulent combustion, only allow determination of the six in-plane velocity gradients upstream of the flame front. In the reported study, high-speed (10 kHz) dual-plane stereoscopic particle image velocimetry (PIV) measurements are conducted on a turbulent swirling jet to spatially, temporally and fully resolve the nine-component velocity-gradient tensor, which is critical for accurate determination of the flame-stretch rate in turbulent combustion. Three key issues facing dual-plane PIV measurements are addressed, namely precise alignments of the two parallel PIV planes, refinements of the PIV-plane separation and optimal procedures for determination of the velocity gradients. Successful high-speed dual-plane stereoscopic PIV measurements as well as complete and accurate determination of the nine-component velocity-gradient tensor are demonstrated.