CPCE CFD Post-Processing, Validation & Verification 2

Question 1

What does a Poincaré section (or phase portrait) reveal during post-processing of time-dependent CFD results?

Accepted Answer

The periodic or chaotic structure of unsteady flow dynamics

Answer

A Poincaré section samples the phase-space trajectory at regular intervals, revealing whether flow dynamics are periodic, quasi-periodic, or chaotic — essential for unsteady flow analysis.

Question 2

Richardson extrapolation in CFD is used to:

Accepted Answer

Estimate the exact solution by extrapolating solutions from two or more grid levels

Answer

Richardson extrapolation combines solutions from systematically refined grids to estimate the continuum (grid-independent) solution and quantify the order of spatial discretization error.

Question 3

In validation of a CFD simulation against experimental data, 'validation uncertainty' accounts for:

Accepted Answer

The combined uncertainties from the simulation and the experimental measurement

Answer

Validation uncertainty includes both the simulation numerical uncertainty and the experimental measurement uncertainty, since comparison is only meaningful when both sources of error are quantified.

Question 4

A velocity vector plot in CFD post-processing shows arrows proportional to speed. What does a region of densely packed, curling arrows typically indicate?

Accepted Answer

A recirculation zone or vortex in the flow field

Answer

Densely packed, curling velocity vectors indicate a recirculation or vortex region where fluid revolves around a local center, a common feature downstream of bluff bodies or in separated flows.

Question 5

Which post-processing quantity is most useful for identifying regions of potential cavitation in liquid flow simulations?

Accepted Answer

Local static pressure compared to the fluid's vapor pressure

Answer

Cavitation occurs when local static pressure drops below the vapor pressure of the liquid; post-processing pressure contours against the vapor pressure threshold identifies cavitation-prone regions.

(CPCE) Certified Professional CFD Engineer Practice Test

(CPCE) Certified Professional CFD Engineer Practice Test

CPCE CFD Post-Processing, Validation & Verification 2