Turbulent Energy Dissipation Rate and Turbulence Scales in the Blade Region of a Self-Aspirating Disk Impeller

Instantaneous radial and axial velocitieques of water in the tank with a self-aspirating disk impeller operating without gas dispersion were measured by the PIV method. A comparison of mean square velocity pulsations confirmed previous observations that the area in which turbulence is non-isotropic is small and extends about 3 mm above and under the impeller and radially 12,5 mm from the impeller blade tip. Based on velocity measurements, the distributions of energy dissipation rates were determined using the dimensional equation  = C·u’3/D and Smagorinsky model. Adoption of the results of the dimensional equation as a reference valueallowed us to determine the Smagorinsky constant value. This value appeared to be smaller than the valuesgiven in the literature. It has been shown that eddies in a small space near the impeller had sufficient energy tobreak up gas bubbles flowing out of the impeller. Based on the obtained energy dissipation rate distributions,appropriate turbulence scales were determined.