On the trailing vortices around hydrofoil impeller blades

The trailing vortices around the profiled blades of a novel axial flow impeller were investigated with angle-resolved laser-Doppler anemometry techniques in a stirred vessel of diameter T = 100 mm. The impeller was of diameter D = T/3 and located at a clearance of C = T/3. The measurements showed that a single vortex is formed behind each blade; the axes of the vortices are inclined at 13 degrees to the horizontal and remain at a constant radius of r/T = 0.14. The kinetic energy of turbulence, k, reaches maxima of 0.0175 V-tip(2) in the vortices, while away from the blades k/V-tip(2) values do not exceed 0.0025. The effect of the vortices on the mean flow and turbulence structure is discussed and the implications of the results for mixing process design are assessed.