CPCE Mesh Generation & Boundary Conditions Flashcards
6 cards from real CPCE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 CPCE Mesh Generation & Boundary Conditions flashcards as text
What does 'wall function' approach mean in turbulent CFD simulations?
Answer: Empirical semi-analytical functions that bridge the wall viscous sublayer and the fully turbulent region, allowing coarser near-wall meshes
Wall functions use empirical profiles (log-law of the wall) to model the near-wall region without resolving the viscous sublayer, enabling coarser meshes (y+ 30–300) near solid boundaries.
In CFD mesh generation, what is the difference between 'refinement' and 'coarsening'?
Answer: Refinement decreases cell size (adds cells) in a region; coarsening increases cell size (removes cells) in a region
Refinement subdivides cells into smaller ones to improve resolution in critical areas, while coarsening merges cells into larger ones to reduce computational cost in regions of low interest.
What is a 'mass flow inlet' boundary condition and when is it preferred over a velocity inlet?
Answer: It specifies the mass flow rate directly; preferred when the mass flux is known and must be precisely controlled
A mass flow inlet prescribes the mass flow rate entering the domain, ensuring exact conservation of mass flux; it is preferred over velocity inlet when the mass flow rate is the known design parameter.
What is 'overset' (or Chimera) meshing and when is it used in CFD?
Answer: A mesh that overlaps multiple zones, allowing relative motion between components without remeshing
Overset (Chimera) meshing uses overlapping mesh zones where data is interpolated between them, enabling simulation of moving bodies (e.g., rotating propellers, pitching airfoils) without remeshing.
What is the 'outflow' boundary condition in CFD and what assumption does it make?
Answer: It extrapolates interior values to the outlet boundary; assumes fully developed flow with zero normal gradients
The outflow boundary condition extrapolates all flow variables from interior cells to the outlet, assuming the flow is fully developed (zero streamwise gradients) at the exit plane.
In adaptive mesh refinement (AMR) for CFD, what criterion is most commonly used to trigger local mesh refinement?
Answer: High solution gradient or error estimator exceeding a user-defined tolerance
AMR typically refines cells where the solution gradient (e.g., of velocity, pressure, or temperature) is large or where an error estimator flags insufficient resolution, concentrating cells where they are most needed.