Most measurements of turbulence in a mixing vessel have shown that the relative intensities were higher than 50%. 2'3'7'9'13" 15) Rao and Brodkey13) pointed out that a flat-blade impeller caused random movementof the impeller stream. Mujumdar et al. 1) and Gunkel et al. 3) attempted to separate the velocity fluctuations into randomandperiodic components. Van't Riet and Smith16) found a trailing vortex that originated in the region behind the upper and lower edges of the blade of the turbine impeller. They introduced the pseudo-turbulence concept, which is that mostof the velocity fluctuations detected by a stationary probe in the discharge stream are largely dependent on the trailing vortex. 17) Subsequent works have extensively investigated the trailing vortex flow. 1'5'6'15'Recently, Yianneskis et al. 18) determined experimentally the structure of the trailing vortex produced by a disc turbine, using LDV technique.