Figure
3. Contours of the instantaneous Y+ values for
the MBC agitator
The time-dependent power spectrum is another criterion to evaluate the
prediction accuracy. The radial velocities at three locations (point
a1, a2, a3, as shown in
Figure 2b, i.e. at the top, middle, and bottom of the composite blade,
respectively), are then sampled and the corresponded power spectrums are
shown in Figure 4. We can see that the energy spectrums all have obvious
peaks at 6 Hz or 12 Hz, which is consistent with the blade passing-by
frequency. The decline line with a slope of −5/3 appears at 2-20 Hz,
which lies in the range of more than one order magnitude of the
frequency. Then the power spectrum decreases sharply when f> 20 Hz due to the energy dissipation. All these indicates
that the anisotropic large eddies and those isotropic small eddies have
been separated successfully in the numerical simulations and the energy
is transported from the macro-flow eddies to the dissipated small
eddies.