CPCE CPCE Turbulence Modeling & Numerical Methods

Question 1

Which turbulence model is known as a two-equation model that solves transport equations for turbulent kinetic energy (k) and its dissipation rate (ε)?

Accepted Answer

k-ε model

Answer

The k-ε model solves two transport equations for turbulent kinetic energy k and its dissipation rate ε to close the Reynolds-averaged Navier-Stokes equations.

Question 2

What does the acronym 'DNS' stand for in the context of CFD turbulence simulation?

Accepted Answer

Direct Numerical Simulation

Answer

DNS (Direct Numerical Simulation) resolves all turbulent length and time scales without any turbulence modeling, making it highly accurate but computationally expensive.

Question 3

The Courant-Friedrichs-Lewy (CFL) condition is primarily a stability criterion for which class of numerical methods?

Accepted Answer

Explicit time-stepping schemes

Answer

The CFL condition restricts the time step size in explicit time-stepping schemes to ensure numerical stability by requiring that information does not travel more than one cell per time step.

Question 4

In Large Eddy Simulation (LES), what role does the Sub-Grid Scale (SGS) model play?

Accepted Answer

It models the effect of eddies smaller than the grid size

Answer

The SGS model in LES accounts for the influence of small unresolved eddies (smaller than the grid cell size) on the resolved larger-scale flow.

Question 5

Which numerical discretization scheme is second-order accurate in space and is commonly used for convection terms in CFD to balance accuracy and stability?

Accepted Answer

Central differencing

Answer

Central differencing is second-order accurate in space and provides a good balance between accuracy and stability for convection term discretization in CFD.

(CPCE) Certified Professional CFD Engineer Practice Test

(CPCE) Certified Professional CFD Engineer Practice Test

CPCE CPCE Turbulence Modeling & Numerical Methods