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.