Tomographic stereo-PIV measurement of 3D flow patterns and local power dissipation in a stirring blade turning space in transitional flow regime

• Tomographic stereo-PIV elucidated 3D flow patterns in stirring blade turning space. • Discharge flow forms in front and behind blades in high-viscosity transition regime. • Dominant discharge flow formed behind blades in low-viscosity transition regime. • In transition regime, tangential flow speed behind blades exceeded impeller’s speed. • Evaluated local energy dissipation in discharge flow via a fluid deformation tensor. This study employed two-dimensional and two-component particle image velocimetry (2D2C-PIV) and tomographic-stereo PIV (TS-PIV) for flow analysis. The setup used four high-speed cameras for three-dimensional and three-component measurements to describe the three-dimensional flow pattern and energy dissipation rate in the rotating radius of a six-blade paddle under transitional flow. Results demonstrate that fluid overcoming from the top and bottom edges of the blade is discharged horizontally at both the front and back sides of the blades in the high-viscosity transition regime. In the low-viscosity transition regime, discharge flow from the blade back is greater than that from the front side of the blade. In this regime, the laminar shear flow-dominated region—evaluated by the fluid strain rate tensor—was concentrated around the impeller blade. Additionally, the turbulent dissipation-dominated region is distributed along the discharge flow from the middle of the two blades until the tail of the discharge flow.