Figure7. Profiles of the dimensionless radial and axial velocity fluctuations at two radial positions on the plane of P45. (a)Urms,r , r /R =0.7; (b)Urms,r , r /R =0.9; (c)Urms,a , r /R =0.7; (d)Urms,a , r /R =0.9.
Turbulent characteristics
In this part, instantaneous vorticity field obtained by TR-PIV is first used to evaluate the macroscopic distribution of large anisotropic eddies in the tank, which directly determine the mixing performance of the MBC agitator. In general, more uniform macroscopic eddies implies that good mixing efficiency can be achieved24.
Figure 8 shows five coherent instantaneous vorticity distributions on the sampling plane of P45, with a time interval of 0.05 s. The total time is 0.2 s, during which a composite blade passes by the sampling plane. Here, Figure 8c is the case in which the blade just passes by. It is observed that anisotropic eddies of about 0.25R in size are uniformly distributed along the axial direction, no matter where the composite blade is. This characteristic makes intuitive sense: the mass exchange along the axial direction can be achieved well, and the turbulent kinetic energy will be more evenly distributed.