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.