Stereo-PIV measurement of turbulence characteristics in a flow mixer

Three-component, turbulent flow measurements are performed using stereo PIV technique, in a cylindrical, stirred, water-flow mixer, with commercially available HR-100 as the impeller, which has three identical blades, separated by 120A degrees with each other. The flow is analyzed at twelve axisymmetric, vertical planes, with the regular angular interval of 10A degrees, so that the 12 planes cover the whole 120A degrees separation between any two of the impeller blades. The results show that the turbulence mixing below the impeller is much higher than that above it, as the bulk fluid motion convects down the turbulence produced at the blade-water interfaces. Moreover, vortices with high level of turbulence, overwhelmingly dominated by the tangential velocity fluctuations, are created near the tips of the blades and convected downward, with their turbulence gradually dissipating with time. When these vortices are connected throughout the domain, they constitute three disconnected, helical arcs, each of which is connected to the tip of a blade and extends downward in the opposite direction to the rotation of the impeller. The arcs rotate with the same angular velocity of the impeller. The mean velocity and turbulence statistics of the flow are discussed at each of the alternate measurement planes.