Turbulent Flow: Theory & CFD Modeling

A: This selection gives stable pressure-drop predictions without forcing mesh refinement that the schedule won't tolerate. Option B can work but drives y+ and cell count into a corner you didn't budget. Option C is aimed at attached external flows and misses separation physics here. Option D ignores compute reality and adds no safety margin.

A: This step confirms numerical error is under control before you compare physics. Option B assumes the mesh is already adequate, which is backward. Option C tunes numerics to match data and hides discretization error. Option D checks a local metric only after global correlation has already biased you.

A: This outcome directly skews friction and thermal loads, which feeds into unsafe design decisions. Option B is a time-stepping issue, not a wall-resolution one. Option C can happen but isn't the primary consequence of high y+ misuse. Option D is unrelated to wall treatment entirely.

A: This value correctly uses RMS over mean, matching how solvers define intensity. Option B divides by the wrong velocity scale. Option C doubles the RMS without justification. Option D mixes RMS with peak assumptions and overstates turbulence.

A: This approach captures large-scale unsteadiness without blowing the compute budget. Option B suppresses the very physics driving noise. Option C trades relevance for academic purity. Option D adds time dependence but still damps the separation structures.

A: This check ensures the solution isn't violating conservation at the system level. Option B can look clean while the overall balance is still wrong. Option C is model-internal and not a pass criterion. Option D mixes validation with verification.

A: This failure mode directly affects load paths and can sink a design review. Option B is the opposite of k-ε behavior. Option C is rarely the problem with this model. Option D is not its typical weakness.

A: This scale correctly reflects (ν³/ε)^(1/4), showing why DNS is impractical here. Option B misplaces a decimal in the fourth-root step. Option C ignores viscosity entirely. Option D tweaks properties without changing the math enough to justify the jump.

A: This step targets a boundary condition that directly drives loss without changing model form. Option B hides the root cause and won't survive audit. Option C assumes the error location without evidence. Option D resets correlation history on the last day.