CPCE CFD Post-Processing, Validation & Verification 1

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

A streamline is a curve that is instantaneously tangent to the velocity vector at every point, representing the direction of flow at a specific time instant.

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

The Grid Convergence Index (GCI) is the standard metric recommended by ASME and AIAA to quantify spatial discretization uncertainty using Richardson extrapolation across refined grids.

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

The Q-criterion identifies vortices by locating regions where the rotation rate tensor dominates the strain rate tensor (Q > 0), making it useful for visualizing coherent vortical structures.

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

Verification confirms that the mathematical model is solved correctly — i.e., the numerical implementation is free of coding errors and discretization converges — without regard to whether the model represents reality.

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

True convergence in steady-state CFD is indicated when residuals have leveled off (not necessarily at machine precision) and engineering quantities of interest such as drag, lift, or mass flow rate have stabilized.

(CPCE) Certified Professional CFD Engineer Practice Test

(CPCE) Certified Professional CFD Engineer Practice Test

CPCE CFD Post-Processing, Validation & Verification 1