CPCE CFD Software & Simulation Techniques 2 — Questions and Answers
Question 1: In ANSYS Fluent, which discretization scheme is typically recommended for achieving second-order accuracy in convection terms?
- First-order upwind
- Second-order upwind (Correct answer)
- Power law
- Central differencing
Correct answer: Second-order upwind
Second-order upwind scheme reduces numerical diffusion compared to first-order upwind by using a wider stencil for gradient reconstruction.
Question 2: Which CFD software uses the OpenFOAM framework as its underlying solver engine?
- STAR-CCM+
- SimScale (Correct answer)
- ANSYS CFX
- Fluent
Correct answer: SimScale
SimScale is a cloud-based CFD platform that uses OpenFOAM as its core solver for incompressible and compressible flow simulations.
Question 3: What does the term 'AMG' stand for in the context of CFD iterative solvers?
- Adaptive Mesh Generation
- Algebraic MultiGrid (Correct answer)
- Automatic Mesh Gradation
- Anisotropic Mesh Grading
Correct answer: Algebraic MultiGrid
Algebraic MultiGrid (AMG) is a solver acceleration technique that coarsens the algebraic problem rather than the mesh, speeding convergence for large linear systems.
Question 4: In OpenFOAM, what is the purpose of the 'fvSolution' dictionary?
- Defines mesh refinement levels
- Specifies linear solvers and convergence tolerances (Correct answer)
- Sets boundary condition types
- Controls time-stepping parameters
Correct answer: Specifies linear solvers and convergence tolerances
The fvSolution dictionary in OpenFOAM specifies the linear algebra solvers, preconditioners, and convergence criteria for each transported quantity.
Question 5: Which technique is used in CFD to handle moving boundaries or rotating machinery by allowing mesh blocks to slide past each other?
- Overset (Chimera) mesh
- Sliding mesh interface (Correct answer)
- Adaptive mesh refinement
- Polyhedral meshing
Correct answer: Sliding mesh interface
Sliding mesh interfaces allow adjacent mesh zones to rotate or translate relative to each other while exchanging flux information across the interface.
Question 6: What is the primary advantage of using hex-dominant meshing over fully tetrahedral meshing in structured flow regions?
- Lower cell count for equivalent accuracy (Correct answer)
- Easier surface mesh generation
- Reduced solver memory requirements
- Better handling of complex geometry
Correct answer: Lower cell count for equivalent accuracy
Hexahedral cells align with the flow direction and require fewer cells to achieve equivalent accuracy compared to tetrahedral cells, reducing computational cost.
Question 7: In the SIMPLE algorithm, what does the pressure correction equation enforce?
- Momentum conservation
- Continuity (mass conservation) (Correct answer)
- Energy conservation
- Turbulence kinetic energy balance
Correct answer: Continuity (mass conservation)
In SIMPLE, the pressure correction equation is derived from the continuity equation to ensure that the velocity field satisfies mass conservation after each iteration.
CPCE CFD Software & Simulation Techniques 2
In ANSYS Fluent, which discretization scheme is typically recommended for achieving second-order accuracy in convection terms?