CPCE Computational Fluid Dynamics Theory & Principles 4

Question 1

The PISO (Pressure Implicit with Splitting of Operators) algorithm differs from SIMPLE primarily in that it:

Accepted Answer

Performs multiple pressure corrections per time step without inner iterations

Answer

PISO performs a predictor and two (or more) corrector steps per time step, making it more suitable for transient flows than SIMPLE's iterative approach.

Question 2

Which type of mesh is most suitable for complex geometries due to its ability to conform to curved boundaries?

Accepted Answer

Unstructured mesh with triangles/tetrahedra

Answer

Unstructured meshes with triangular or tetrahedral elements can conform to arbitrarily complex geometries, making them ideal for industrial CFD applications.

Question 3

The 'checkerboard' pressure instability in co-located grid arrangements arises because:

Accepted Answer

Pressure and velocity are evaluated at the same locations, decoupling alternating pressure modes

Answer

On co-located grids, standard central differencing for the pressure gradient does not sense a checkerboard pressure field, allowing spurious oscillatory modes to persist.

Question 4

In Reynolds-Averaged Navier-Stokes (RANS) modeling, the Reynolds stress tensor arises from:

Accepted Answer

Time-averaging the nonlinear convective term, yielding correlations of velocity fluctuations

Answer

Time-averaging the nonlinear u·∇u term produces the Reynolds stress tensor −ρ⟨u'u'⟩, which must be modeled to close the RANS equations.

Question 5

The wall-y⁺ parameter is used to determine whether:

Accepted Answer

The mesh is fine enough to resolve the viscous sublayer or if wall functions should be used

Answer

y⁺ = u_τ·y/ν indicates the location of the first mesh point in wall units; y⁺ < 5 implies the viscous sublayer is resolved, while y⁺ ≈ 30–300 suits wall functions.

(CPCE) Certified Professional CFD Engineer Practice Test

(CPCE) Certified Professional CFD Engineer Practice Test

CPCE Computational Fluid Dynamics Theory & Principles 4