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At this stage, the turbulence model that was going to be used for modeling was set up. Standard k-ε was used as the turbulence model. After this, the material was defined. Water was selected from the FLUENT database as working fluid. After defining operating conditions and making sure that the boundary conditions set in Gambit was correct, the initial conditions were set up. Finally, the solution was obtained by iterating until the solution was converged. With the solution obtained, various results were then analyzed.
2.5 Mesh Sensitivity Analysis
The effect of number of mesh elements on the result was also carry out. Coarse mesh, medium mesh and fine mesh were created and the result from each mesh were compared. This analysis will provide confidence on the accuracy of certain mesh. If the changes in mesh elements does not result in a lot of change in result,
2.6 Parameterization
At the later stage of project, after the good solution was obtained, the effect of geometry on results was analyzed. Different clearance height was used for analyzing new results as a result of this effect. It would be tedious to individually recreate each geometry and mesh for different clearance height from scratch. For this reason, parameterization technique was used. The original Gambit journal file was modified to include the variable clearance height. Using this method, changes in corresponding clearance height was plug into the journal file and run using Gambit to obtain desired mesh and geometry. The journal files used for such parameterization is included in the Appendix.
2.6 Comparing Turbulence Model
Different turbulence model were also used
3. Results and Discussions
Some of the important results are the velocity vectors, contour of pressure coefficient, contours of pressure coefficient, contours of strain rate and contours of turbulence dissipation rate.
Figure 5: Velocity Vectors (Click on figure for original size)
Velocity vector plot shows the velocity of the fluids throughout the flocculator. As can be seen, there is a region of high velocity at the outer turn and recirculation at the inner turn. At the bottom of the flocculator, there is region of stagnant fluid.
Figure 6: Contours of Stream Function (Click on figure for original size)
Contours of stream function tell us how the fluid travel in the flocculator. As can be seen from figure 6, there is enclosed streamline at the inner turn. The enclosed streamlines means there are recirculating fluid which are trapped in the region.
Figure 7: Contours of Pressure Coefficient
Figure 7 shows most of the pressure coefficient drop occurs around the bend. There is a pressure coefficient drop of about 3.7 across the bend. (Talk about the experimental result. Literature review data)
Figure 8: Contours of Strain Rate
Contours of strain rate shows high strain rate right before and after the turn. There are also high strain rate near the wall. The region with high strain rate is the region where the flocculation occurs.
Figure 9: Contours of Turbulent Disssipation Rate
Contours of turbulent dissipation rate shows about the same trend as the contours the strain rate right after the turning. The region of high turbulence dissipation after the turn is about twice the length of baffle spacing (research literature). The high dissipation rate after the turn is because of the expansion of the fluid.