CPCE CPCE Mesh Generation & Boundary Conditions 3

Question 1

What does 'wall function' approach mean in turbulent CFD simulations?

Accepted Answer

Empirical semi-analytical functions that bridge the wall viscous sublayer and the fully turbulent region, allowing coarser near-wall meshes

Answer

A mathematical function describing wall roughness geometry

Answer

A boundary condition enforcing constant heat flux at walls

Answer

A special meshing technique for curved surfaces

Question 2

In CFD mesh generation, what is the difference between 'refinement' and 'coarsening'?

Accepted Answer

Refinement decreases cell size (adds cells) in a region; coarsening increases cell size (removes cells) in a region

Answer

Refinement increases cell size; coarsening decreases cell size

Answer

Refinement applies only to tetrahedral meshes; coarsening applies only to hexahedral meshes

Answer

Refinement is a post-processing step; coarsening is a pre-processing step

Question 3

What is a 'mass flow inlet' boundary condition and when is it preferred over a velocity inlet?

Accepted Answer

It specifies the mass flow rate directly; preferred when the mass flux is known and must be precisely controlled

Answer

It specifies velocity and turbulence; preferred for low Reynolds number flows

Answer

It specifies total temperature; preferred for compressible flow inlets

Answer

It specifies total pressure; preferred for internal duct flows

Question 4

What is 'overset' (or Chimera) meshing and when is it used in CFD?

Accepted Answer

A mesh that overlaps multiple zones, allowing relative motion between components without remeshing

Answer

A mesh type exclusive to structured hexahedral grids

Answer

A mesh refinement approach for shock-capturing in supersonic flows

Answer

A method to automatically coarsen meshes in low-gradient regions

Question 5

What is the 'outflow' boundary condition in CFD and what assumption does it make?

Accepted Answer

It extrapolates interior values to the outlet boundary; assumes fully developed flow with zero normal gradients

Answer

It sets a fixed pressure at the outlet; assumes subsonic exit conditions

Answer

It enforces a velocity profile at the outlet; assumes turbulent pipe flow

Answer

It applies a symmetry condition at the exit; assumes no normal flux

Question 6

In adaptive mesh refinement (AMR) for CFD, what criterion is most commonly used to trigger local mesh refinement?

Accepted Answer

High solution gradient or error estimator exceeding a user-defined tolerance

Answer

Maximum cell volume exceeding a threshold

Answer

Wall distance exceeding a specified y+ value

Answer

Solver residual exceeding convergence tolerance