CPCE Computational Fluid Dynamics Theory & Principles 3

Question 1

Which turbulence model solves two transport equations — one for turbulent kinetic energy and one for its dissipation rate?

Accepted Answer

k-ε model

Answer

The k-ε model solves transport equations for turbulent kinetic energy k and its dissipation rate ε, making it a two-equation RANS model.

Question 2

The CFL (Courant-Friedrichs-Lewy) condition states that for explicit schemes the time step must satisfy:

Accepted Answer

CFL = u·Δt/Δx ≤ 1

Answer

The CFL condition CFL = u·Δt/Δx ≤ 1 ensures that information cannot travel more than one cell per time step for explicit convection schemes.

Question 3

In Large Eddy Simulation (LES), the role of the subgrid-scale (SGS) model is to:

Accepted Answer

Model the effect of unresolved small-scale eddies on the resolved flow

Answer

LES explicitly resolves large eddies but models the energy drain from resolved scales to unresolved small eddies via SGS models.

Question 4

The QUICK scheme (Quadratic Upstream Interpolation for Convective Kinematics) is third-order accurate and uses:

Accepted Answer

Two upstream and one downstream node for interpolation

Answer

QUICK fits a quadratic through two upstream and one downstream node to interpolate face values, achieving third-order spatial accuracy.

Question 5

Which statement best describes the concept of 'multigrid' in CFD solvers?

Accepted Answer

Accelerating convergence by solving residual equations on coarser grids

Answer

Multigrid methods use a hierarchy of coarser grids to efficiently damp error modes of all wavelengths, dramatically accelerating iterative solver convergence.

(CPCE) Certified Professional CFD Engineer Practice Test

(CPCE) Certified Professional CFD Engineer Practice Test

CPCE Computational Fluid Dynamics Theory & Principles 3