CPCE CFD Post-Processing, Validation & Verification 3

Question 1

What is the purpose of computing the 'pressure coefficient' (Cp) distribution in external aerodynamics CFD post-processing?

Accepted Answer

To non-dimensionalize pressure for comparison across different flow speeds and geometries

Answer

To compute the Reynolds number distribution along the body surface

Answer

To measure the temperature variation along the aerodynamic surface

Answer

To determine the turbulent intensity at the boundary layer edge

Question 2

In a CFD report for engineering design, which information is essential to include for the simulation to be reproducible?

Accepted Answer

Solver settings, mesh statistics, boundary conditions, turbulence model, and convergence criteria

Answer

Color schemes used in post-processing images

Answer

The CPU clock speed used during computation

Answer

Only the final contour plots of velocity and pressure

Question 3

Which approach is used to extract a boundary layer velocity profile from a CFD solution for comparison with the Blasius or log-law theoretical profiles?

Accepted Answer

Sampling velocity data along a line normal to the wall at a specific streamwise location

Answer

Integrating the turbulent kinetic energy normal to the wall

Answer

Computing the divergence of the velocity field near the wall

Answer

Averaging the wall shear stress over the entire wetted surface

Question 4

The 'effective viscosity ratio' (μt/μ) in post-processing of RANS simulations indicates:

Accepted Answer

The local importance of turbulent mixing relative to molecular viscosity

Answer

The ratio of laminar to turbulent boundary layer thickness

Answer

The quality of the near-wall mesh in the turbulent region

Answer

The degree to which the flow is compressible at that location

Question 5

Which numerical artifact can appear in CFD results when using a first-order upwind scheme on a coarse mesh, and is revealed during post-processing?

Accepted Answer

Numerical diffusion — excessive smearing of sharp gradients and shocks

Answer

Gibbs phenomenon — spurious oscillations near sharp gradients

Answer

Aliasing error — false high-frequency modes in the solution

Answer

Lax-Wendorff dispersion — phase speed errors in wave propagation

Question 6

In post-processing of combustion CFD results, the 'mixture fraction' variable is used to:

Accepted Answer

Track the local composition between pure fuel and pure oxidizer streams

Answer

Measure the local ratio of turbulent to laminar flame speed

Answer

Quantify the heat release rate per unit volume

Answer

Determine whether the flame is premixed or non-premixed based on temperature

Question 7

When performing uncertainty quantification (UQ) in CFD using Monte Carlo sampling, the primary reason for the large number of required simulations is:

Accepted Answer

Statistical convergence of output statistics requires many independent input samples

Answer

Each simulation uses a different turbulence model that must be averaged

Answer

Each Monte Carlo run must use a progressively finer mesh

Answer

The method requires iterative coupling between CFD and structural solvers