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

The spatial distribution of pressure at a fixed time step

Answer

The location of shockwaves in supersonic flows

Answer

The cumulative mass flux through a control surface

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

Accelerate solver convergence by extrapolating residuals

Answer

Reduce interpolation error when mapping results between non-matching grids

Answer

Extrapolate boundary condition profiles from coarse to fine meshes

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

Only the numerical discretization error in the CFD solution

Answer

The error introduced by incorrect boundary condition specification

Answer

The difference in turbulence models between two CFD codes

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

A zone of laminar flow with uniform velocity profiles

Answer

A region where the mesh is too coarse to resolve gradients

Answer

The location of an inlet boundary condition

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

Turbulent kinetic energy (TKE)

Answer

Wall shear stress distribution

Answer

Temperature gradient magnitude

Question 6

The concept of 'observed order of accuracy' in a grid refinement study is determined by:

Accepted Answer

Computing the ratio of errors on successive grid levels using a known formula involving the refinement ratio

Answer

The theoretical order of the numerical scheme specified in the solver manual

Answer

The number of iterations required for convergence on each grid

Answer

Comparing the CFL number across different mesh resolutions

Question 7

When comparing CFD results with Particle Image Velocimetry (PIV) experimental data, which consideration is most important for a fair comparison?

Accepted Answer

Matching the spatial resolution and interrogation window size of PIV with the CFD data extraction plane

Answer

Ensuring both datasets use the same color map for visualization

Answer

Running the CFD simulation and the experiment at the same computer time

Answer

Using the same turbulence model as the one assumed in the PIV algorithm