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Figure 16 clearly shows the recirculation region for the three different turbulence models. Since standard K-ε model best represent the flow features seen in the demo plant, it is concluded that standard K-e model best simulate the turn.
I am uncomfortable with the method of selecting the turbulence model. The demonstration plant is in the laminar flow region and thus it may not be a good reference point for full scale turbulent reactors. The difference between the various models is quite significant especially when you consider that we are most interested in Gθ. The models that predict a large wake behind the expansion will also predict lower average values of the energy dissipation rate and that will correlate with a larger Gθ. Thus we need a better basis for choosing the model that we will use for further research. I suggest further research to determine which models do a better job of modeling the evolution of a turbulent jet. The region where the models diverge significantly is in their predictions about the length of the zone influenced by the jet.
4. Conclusions
- An area of recirculation occurs near the center wall immediately after the turn
- Pressure coefficient drop over one baffle turn is 3.75
- After a clearance height of one baffle spacing or greater, the pressure coefficient drop and the maximum velocity becomes constant
- Most of the energy dissipation occurs in the region after the turn over a distance of about two baffle spacings
- The pressure coefficient drop is insensitive to the Reynolds number for a large range of inlet velocities
- A mesh with 20,000 mesh elements is sufficient to obtain accurate results
- Different turbulence model resulted in fairly different results
- The standard k-e model best simulates the turn
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