CPCE CFD Software & Simulation Techniques 4

Question 1

In CFD, what is 'operator splitting' used for in time integration?

Accepted Answer

Treating different physics operators with separate integration steps

Answer

Operator splitting (e.g., Strang splitting) integrates different physics terms (advection, diffusion, source) in separate sub-steps, allowing use of optimal schemes for each.

Question 2

What is the key advantage of the Detached Eddy Simulation (DES) approach over pure LES for high-Reynolds-number external flows?

Accepted Answer

DES uses RANS near walls to reduce near-wall mesh cost while using LES away from walls

Answer

DES is a hybrid method that applies RANS in attached boundary layers (where full LES is prohibitively expensive) and LES in separated regions where large eddies dominate.

Question 3

In ANSYS Fluent, which boundary condition type is most appropriate when the total pressure and total temperature at an inlet are known?

Accepted Answer

Pressure inlet

Answer

The pressure inlet boundary condition in Fluent accepts total (stagnation) pressure and temperature, making it appropriate when those quantities are known at the inlet.

Question 4

Which numerical scheme is known for its ability to capture shock waves sharply without spurious oscillations in compressible flow simulations?

Accepted Answer

TVD (Total Variation Diminishing) scheme

Answer

TVD schemes apply flux limiters to suppress oscillations near discontinuities (shocks) while maintaining high-order accuracy in smooth flow regions.

Question 5

What does 'GCI' (Grid Convergence Index) measure in CFD verification?

Accepted Answer

Discretization error estimate using Richardson extrapolation on multiple mesh levels

Answer

GCI provides a quantitative estimate of discretization error by applying Richardson extrapolation to solutions on systematically refined meshes.

(CPCE) Certified Professional CFD Engineer Practice Test

(CPCE) Certified Professional CFD Engineer Practice Test

CPCE CFD Software & Simulation Techniques 4