Abstract: Particle image velocimetry(PIV)technique is used to study the flow field in stirred tank with Rushton turbine and without baffles. Particle images are captured at six different blade positions under the conditions of rotating speed and Reynolds number being 240 r/min and 1 527, respectively. By processing and calculating the particle images, phase-averaged and mean velocity fields are obtained, and the velocity distribution profiles are also presented. The results shows that the impeller stream of the Rushton turbine is not symmetrical, but skewing downwards. Closing to the impeller tip, the radial velocity is higher than other parts. Away from the blade tip, radial velocity is getting smaller and smaller. Therefore, the impeller stream behaves like a free jet：the fluid is ejected from the impeller blades into a mass of slowly-moving fluid and it spread out vertically and entrains a considerable amount of surrounding fluid into it outer parts and make more fluid mix and react.

Key words: Mean flow field, PIV(Particle image velocimetry), Rushton turbine, Stirred tank, aerodynamic loads, operational safety, stochastic winds, wind angle, high-speed train