CPCE CFD Software & Simulation Techniques 5

Question 1

What is the primary purpose of 'conjugate heat transfer' (CHT) simulations in CFD?

Accepted Answer

Solve coupled fluid flow and solid conduction simultaneously

Answer

CHT simulations solve the energy equations in both fluid and solid domains simultaneously, accounting for conduction within solids coupled to convection in the fluid.

Question 2

In CFD mesh generation, what is 'aspect ratio' and why is a high aspect ratio problematic in non-flow-aligned directions?

Accepted Answer

Ratio of the longest to shortest edge of a cell; high values cause numerical errors in cross-flow gradients

Answer

Cells with high aspect ratio aligned perpendicular to the flow gradient direction introduce significant truncation error and can cause solver instability.

Question 3

Which feature in STAR-CCM+ allows automatic mesh refinement in regions of high flow gradient during a simulation?

Accepted Answer

Adaptive mesh refinement (AMR)

Answer

STAR-CCM+'s AMR feature automatically refines or coarsens mesh cells based on solution-based criteria such as velocity gradient or pressure gradient magnitude.

Question 4

In the context of CFD solver settings, what is 'false diffusion' and which approach minimizes it?

Accepted Answer

Numerical diffusion caused by mesh-flow misalignment with first-order schemes; minimized by higher-order schemes and flow-aligned meshes

Answer

False diffusion arises when flow crosses cell faces obliquely with first-order upwind schemes; using second-order schemes and aligning mesh with the flow reduces it.

Question 5

What role does the 'Courant-Friedrichs-Lewy (CFL) condition' play in transient CFD simulations?

Accepted Answer

Constrains the time step to ensure numerical stability in explicit time-marching schemes

Answer

The CFL condition requires that the time step be small enough that information cannot travel more than one cell per time step, ensuring stability of explicit schemes.

(CPCE) Certified Professional CFD Engineer Practice Test

(CPCE) Certified Professional CFD Engineer Practice Test

CPCE CFD Software & Simulation Techniques 5