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

Model radiation between surfaces only

Answer

Compute only convective heat transfer coefficients

Answer

Apply isothermal wall boundary conditions

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

Ratio of cell volume to surface area; high values cause memory issues

Answer

Ratio of viscous to inertial forces; high values indicate turbulent flow

Answer

Ratio of mesh size to domain size; high values indicate over-refinement

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

Mesh morphing

Answer

Polyhedral conversion

Answer

Surface wrapper

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

Artificial compressibility added to stabilize the solver; minimized by reducing time step

Answer

Diffusion introduced by turbulence models; minimized by DNS

Answer

Diffusion from periodic boundary conditions; minimized by increasing domain size

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

Limits the maximum mesh size

Answer

Specifies the turbulence intensity at inlets

Answer

Determines the convergence tolerance for iterative solvers

Question 6

Which turbulence model is most commonly used for internal flows in ducts and pipes where accurate prediction of near-wall behavior is critical?

Accepted Answer

SST k-ω

Answer

Spalart-Allmaras (SA)

Answer

Standard k-ε with standard wall functions

Answer

Large Eddy Simulation (LES)

Question 7

In CFD post-processing, what is the difference between 'pathlines' and 'streamlines'?

Accepted Answer

Pathlines trace actual particle trajectories in unsteady flow; streamlines are tangent to velocity field at a single instant

Answer

Pathlines show pressure contours; streamlines show velocity vectors

Answer

Pathlines are used only in laminar flow; streamlines only in turbulent flow

Answer

Pathlines represent averaged flow; streamlines represent instantaneous flow