Direct measurement of turbulence structures in mixing jar using PIV

Particle image velocimetry (PIV) is used to measure two-dimensional velocity fields in a standard jar test tank for different impeller speeds. General flow patterns are obtained for the whole tank, and small scale (∼1 cm²) measurements taken at different locations within the jar demonstrate spatial variations of flow characteristics, such as vortex motions near the impeller. Techniques are also developed to derive turbulence dissipation rate and energy intensity as well as local velocity gradient and Kolmogorov microscale for raw PIV data. The results exhibit a consistent general trend with different impeller speeds; for instance, turbulence energy varies directly with mixing intensity. The two-dimensional turbulence field is revealed by using a spatial filtering technique that facilitates calculation of the integral length scale. PIV data are also used to calculate vorticity, which cannot be obtained by more traditional measurement techniques, such as laser-Doppler velocimetry. Overall, PIV represents a significant advance in our ability to characterize the mixing inside a jar test tank.