Learn how to use Ansys Discovery to obtain accurate results in valve performance using the Refine Mode.
Part II: Simulation in Refine Mode
The simulation of valves can be performed in both Explore mode and Refine mode. Explore mode allows for a quick simulation to obtain results in up to 2 minutes with a certain level of accuracy, enabling the evaluation of design changes. This provides a relative comparison to decide on the design that requires a deeper level of computational analysis in Refine mode. Refine mode uses the Fluent solver to obtain results based on a meshed geometry. Then, each model will take much more time to provide results (10-20 min). This second blog explains this approach in detail.
Steps
The geometry is the same as the valve representation in Part I. Thus, the steps begin directly with the meshing process as no modifications are needed for this demo. However, changes can be applied at any time if required.
- Set up
It is important to mention that the 'Cutting Bodies' tool is not available in Refine Mode. When you switch to Refine Mode, you will see an error message if any of the stem/disc positions are enabled. To continue with the simulation, the user will need to subtract the volumes as usual using the 1) Combine tool. Following the steps select 2) the main volume, then 3) the body to be subtracted and 4) the remaining common body.
This means that three additional fluid domains must be created, or the file must be copied and the fluid domain modified accordingly. Nonetheless, it is possible continue using the Parametric table. This means that, by selecting the option 'Update All', the user can run a complete set of simulations for a given Fidelity level. Recall that in Refine mode, as it uses a computational mesh, the simulation time will increase when compared with Explore Mode.
- Meshing
Refine mode allows solving the CFD model based on computational meshes. Global and local controls are available to create the mesh: 1) the Fidelity bar can be used as in the Explore Mode to provide a general refinement, 2) Under the 'Simulation Tab' > Fidelity, the user can select Global or Local buttons. In this Demo, a global control was applied. The default option is 'Determine sizing automatically', but the selected approach was 3) 'Curvature and proximity' as it allows a good level of refinement including the number of inflation layers. Finally, the 4) mesh is created by clicking on the icon shown.
Three meshes were created for this demo to perform the convergence analysis. The fist goal is to determine the Pressure drop vs flow rate curve and compare it with that obtained in the Explore mode. Once the user selects the meshing method, the mesh can be generated using the icon shown in the bottom right corner of the screen 4), which is shown in the picture above. More tools for the simulation can be setup in the 'Simulation Tab' > Physics > 'Simulation Options'.
- Results
For comparison, the curve of the converged solution (Line 1) is plotted on the same graph as the curves obtained in Explore mode.
In Part I, several models were solved for different fidelity values and for each inlet velocities (later used to calculate each flow rate). The graph shows that the converged solution in Refine Mode is similar to the line built from the average of the simulations for each inlet velocity (Line 2). For flow rates smaller than 307 LPM, the pressure drop from Line 1 is slightly smaller than that predicted by Line 2. However, for higher flow rates, the opposite occurs.
Finally, the procedure is repeated for the rest of stem/disc positions involving mesh creation, updating the parameterization table, and obtaining results to obtain the last curve: the resistance coefficient vs. valve opening. Here the converged solution is close to the upper limit predicted by the Explore mode as the fidelity is the highest; however, recall that in Explore mode the user does not have control of the mesh. To summarize, it is always better to run a detailed simulation, but the exploration provides a suitable range.