关键词: V3V, PIV, 尾涡, 涡轮桨, 流场, 各向同性

Abstract:

The flow field nearby standard Rushton impeller in a stirred vessel was investigated by volumetric three-component velocimetry (V3V) measurements, which about 18000 vectors were captured in a cubic volume of approximately 140 mm in height by 140 mm in width by 100 mm in depth. The characteristics of three-dimensional flow field and the structure of trailing vortices were derived from velocity data. The distributions of radial, axial and tangential velocities in 30° cross-section behind the impeller were analyzed and the distributions of radial and axial velocities by V3V were in good agreement with these by 2D-PIV (particle image velocimetry), especially for trailing vortices in the region of discharge streams. The 2D-PIV study on development of trailing vortices shows that the trailing vortices had an upward inclination at an angle of 10° to the horizontal line as a result of influence by the liquid free surface. The traces of movement were asymmetrical between upper and lower trailing vortices in a way that the movement and decay of the lower vortex were slightly faster than the upper one, which is consistent with the V3V results. Further, trailing vortices were still visible at 60° angle behind the impeller blade. Compared results of both V3V and 2D-PIV to that of pseudo-isotropic approximation, the normalized turbulent kinetic energy (k/V_tip) by pseudo-isotropic approximation was overestimated 25%-33% at locations of trailing vortices and the impeller, where turbulence tends to be anisotropic.

Key words: V3V, PIV, trailing vortex, Rushton impeller, flow field, isotropy