DIRECT MEASUREMENT OF TURBULENCE STRUCTURES IN MIXING JAR USING PIV

Particle image velocimetry (PIV) is used to measure two-dimensional ve locity fields in a standard jar test tank for different impeller speed s. General flow patterns are obtained for the whole tank, and small sc ale (similar to 1 cm(2)) measurements taken at different locations wit hin the jar demonstrate spatial variations of flow characteristics, su ch 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. Th e results exhibit a consistent general trend with different impeller s peeds; for instance, turbulence energy varies directly with mixing int ensity. The two-dimensional turbulence held is revealed by using a spa tial filtering technique that facilitates calculation of the integral length scale. PIV data are also used to calculate vorticity, which can not be obtained by more traditional measurement techniques, such as la ser-Doppler velocimetry. Overall, PIV represents a significant advance in our ability to characterize the mixing inside a jar test tank.