Stereo-PIV Measurement of Turbulence Shear Stress in a Stirred Flow Mixer

The turbulence dissipation rate and turbulence shear stress are estimated inside a cylindrical, stirred flow mixer by carrying out Stereo PIV measurements in twelve vertical and three horizontal planes. The flow domain is vertically oriented, filled with the water. A commercially-available, three-blade impeller, HR-100, is used as the agitator. The impeller is mounted near the tip of a thin, rigid shaft, which is aligned along the central axis of the flow domain. The impeller rotates with the constant angular speed of 150RPM, and the Reynolds number based on the impeller diameter and the blade's tip-velocity is equal to 59400. The turbulence statistics in the vertical measurement planes are reported before (Shekhar C, Nishino K, Yamane Y and Huang J, “Stereo-PIV measurement of turbulence characteristics in a flow mixer” Journal of Visualization 15 (2012) pp.293~308), which revealed that the rotation induces a downward, as well as tangential, bulk flow motion, which convects the turbulence generated at the blade-water interface, causing the turbulence level below the impeller to be much higher than the level above it. The present study is the second part of the same project, and reports the turbulence statistics in the horizontal measurement planes. The results show that the turbulence level is high in the area swept by the rotating impeller blades and underneath. However, in the outside region, the turbulence damps down and becomes negligible. The vertical and horizontal measurement results are also combined to estimate the production, convection, viscous diffusion, and turbulence dissipation terms of the turbulence kinetic energy's budget equation, along with the turbulence shear stress, along the lines where the different vertical and horizontal planes intersect.