CPCE CFD Software & Simulation Techniques 3 — Questions and Answers
Question 1: Which ANSYS meshing tool is specifically designed for high-quality boundary layer mesh generation around aerodynamic surfaces?
- ICEM CFD (Correct answer)
- SpaceClaim
- DesignModeler
- TurboGrid
Correct answer: ICEM CFD
ANSYS ICEM CFD provides advanced blocking and structured hexahedral meshing capabilities particularly suited for boundary layer-resolved aerodynamic simulations.
Question 2: In STAR-CCM+, what is the function of the 'Continua' node in the simulation tree?
- Manages post-processing scenes
- Defines physics models and material properties (Correct answer)
- Controls solver iteration settings
- Sets mesh size parameters
Correct answer: Defines physics models and material properties
The Continua node in STAR-CCM+ groups physics continua (fluid, solid) and their associated models, equations of state, and material properties.
Question 3: What is 'wall function' approach in turbulence modeling used to avoid?
- Resolving the laminar sub-layer with fine mesh (Correct answer)
- Computing turbulent kinetic energy
- Applying periodic boundary conditions
- Modeling heat transfer in solids
Correct answer: Resolving the laminar sub-layer with fine mesh
Wall functions use semi-empirical correlations to bridge the laminar sub-layer, avoiding the computational expense of resolving it with a very fine near-wall mesh (y+~1).
Question 4: Which OpenFOAM solver would you use for a steady-state incompressible turbulent flow simulation?
- icoFoam
- simpleFoam (Correct answer)
- rhoCentralFoam
- interFoam
Correct answer: simpleFoam
simpleFoam is OpenFOAM's steady-state incompressible solver using the SIMPLE algorithm, suitable for turbulent flows with RANS models.
Question 5: In CFD post-processing, what is a 'Q-criterion' isosurface used to visualize?
- Shock wave locations
- Vortical structures in turbulent flow (Correct answer)
- Pressure coefficient distribution
- Wall shear stress regions
Correct answer: Vortical structures in turbulent flow
Q-criterion identifies vortical structures where the rotation rate dominates strain rate (Q > 0), making it a standard tool for turbulence vortex visualization.
Question 6: What is the purpose of 'under-relaxation factors' in steady-state CFD solvers like SIMPLE?
- Increase time step size for faster convergence
- Damp updates to flow variables to prevent divergence (Correct answer)
- Refine mesh automatically near high-gradient regions
- Switch between first and second-order schemes
Correct answer: Damp updates to flow variables to prevent divergence
Under-relaxation factors limit the change in field variables between iterations, stabilizing the iterative process at the cost of slower convergence.
Question 7: Which meshing strategy is most appropriate for capturing tip vortex flows in rotating turbomachinery?
- Uniform Cartesian mesh
- Conformal polyhedral mesh with tip gap refinement (Correct answer)
- Surface extrusion only
- 2D axisymmetric mesh
Correct answer: Conformal polyhedral mesh with tip gap refinement
Conformal polyhedral meshing with local refinement in the narrow tip gap region ensures sufficient resolution to capture the complex vortex dynamics in that region.
CPCE CFD Software & Simulation Techniques 3
Which ANSYS meshing tool is specifically designed for high-quality boundary layer mesh generation around aerodynamic surfaces?