...
Since we have unresolvable term in turbulence flow, different turbulence models or "estimation" were created to resolve turbulence flow with different characteristic. To decide on the turbulence model to use, a flow over backstep was compared with the literature experimental data. Figure 1 shows the flow of Re = 48000 over the channel. In the middle of the channel, the flow separate due to the small step size of height h. The flow reattaches at about 7 times the step height further downstream. This flow properties is similar to the 180 degree bend in the flocculation tank where we have flow separation and reattachment downstream (Figure 2).
Figure 1: Flow over backstep in a open channel (Re = 48000, Reattachment length = 7h)
Figure 2: Flow over 180 degree turn in flocculation tank
We compared the back step flow using K-e, K-W SST, K-e realizable, K-e RNG, RSM turbulence models. Table 1 shows the comparison results of different turbulence models.
...