CPCE CFD Post-Processing, Validation & Verification

Question 1

In CFD post-processing, what does a streamline represent?

Accepted Answer

A line tangent to the velocity vector field at every point at a given instant

Answer

The path traced by a fluid particle over time

Answer

A line connecting points of equal pressure in the flow domain

Answer

A contour of constant vorticity magnitude

Question 2

Which metric is used to assess spatial discretization error in CFD by comparing solutions on systematically refined grids?

Accepted Answer

Grid Convergence Index (GCI)

Answer

Courant-Friedrichs-Lewy (CFL) number

Answer

Reynolds Averaging Error (RAE)

Answer

Kolmogorov length scale ratio

Question 3

What is the primary purpose of a Q-criterion isosurface in CFD post-processing?

Accepted Answer

To identify and visualize vortical structures in the flow

Answer

To visualize regions of high pressure gradient

Answer

To show areas where the mesh quality is poor

Answer

To mark zones of flow separation from walls

Question 4

In verification and validation (V&V) of CFD, 'verification' specifically refers to:

Accepted Answer

Ensuring the numerical algorithm correctly solves the governing equations

Answer

Comparing CFD results against experimental data to assess physical accuracy

Answer

Checking that the mesh meets quality thresholds such as skewness and aspect ratio

Answer

Validating that the turbulence model is appropriate for the flow regime

Question 5

When monitoring residuals during a steady-state CFD simulation, which condition best indicates convergence?

Accepted Answer

Residuals plateau at a constant non-zero value and key monitor quantities stabilize

Answer

Residuals exceed 1e-2 for all transport equations

Answer

Residuals oscillate periodically with decreasing amplitude

Answer

Residuals drop to exactly zero for the continuity equation

Question 6

In CFD results, a non-dimensionalized wall distance y+ ≈ 1 is required when using:

Accepted Answer

Low-Reynolds-number turbulence models that resolve the viscous sublayer

Answer

Wall functions in the k-ε model

Answer

Inviscid Euler solvers near solid walls

Answer

Large Eddy Simulation with a coarse near-wall mesh

Question 7

Which technique is used to extract a force coefficient (e.g., drag coefficient) from a CFD solution?

Accepted Answer

Integrating pressure and viscous stress over the body surface and normalizing by dynamic pressure and reference area

Answer

Integrating velocity magnitude over the inlet face

Answer

Computing the gradient of the streamfunction along the wake centerline

Answer

Averaging the total pressure drop across the domain