Performance parameters analysis in 2D - sensitivity analysis: convergence level and boundary condition at the water-air interface
Objective
The preliminary simulation experiments suggested that the results are sensitive to the residual levels the solutions converged to and the boundary conditions defined at the water-air interface. A more detailed sensitivity analysis is discussed in this section to exam the accuracy and validity of the results obtained in the simulation experiments section, with respect to the above two conditions.
Methods and Procedures
An h/b ratio=5 was chosen for both the cases with symmetry(frictionless) and wall(no slip)boundary condition defined at the water-air interface. The solution data were saved for both simulations cases at the residual levels of e-4, e-5 and e-6 were saved and the respondant performance parameters were calculated. (Refer to Method and Procedures sections of either simulation experiments section or preliminary simulation experiments section for the creation of geometries and meshes, and the report summaries about all FLUENT settings).
The choices of h/b=5 and residual levels are decided based on the following:
- The optimal h/b were shown to be 3~5.
- Symmetry boundary condition cases had difficulty in converging to e-5, and e-4 in some cases.
- The results change little from e-5 to e-6.
Results and Discussions
Click here for the results of the 2 series of cases, completely summarized the last two worksheet of the Excel workbook.
As shown in the workbook, the contour of energy dissipation rate changed little judging from eyeball examination, but the calculated performance parameters still showed some variability as the convergence level changes.
And the iteration steps need for each cases at the three different levels:
Conclusions
- Energy dissipation rate contour and quantitative analysis show dependence of performance parameters as a function of h/b ratio, which suggest it worth further investigation.
- Results are very sensitive to convergence levels.
- Symmetric boundary condition makes it difficult to converge.
- Symmetric boundary condition and wall boundary condition may have similar results at good convergence levels (residual below e-6). We can use wall boundary condition to replace symmetry boundary condition to ensure accuracy of the results.
SHOULD DIRECTLY ITERATE TO E-6