CPCE Fluid Flow & Heat Transfer Analysis 5

Question 1

What is the role of the Boussinesq approximation in natural convection CFD simulations?

Accepted Answer

Treats density as constant except in the buoyancy term of the momentum equation

Answer

The Boussinesq approximation treats density as constant throughout except in the gravitational body force term, where density variations due to temperature drive the buoyancy force.

Question 2

In CFD residual monitoring, what do normalized residuals below 10⁻⁴ typically indicate?

Accepted Answer

Adequate convergence for most engineering applications

Answer

Normalized residuals below 10⁻⁴ are generally accepted as indicating adequate convergence for engineering-level accuracy in steady-state CFD simulations.

Question 3

Which phenomenon is captured by the turbulent Prandtl number in CFD heat transfer modeling?

Accepted Answer

The ratio of turbulent momentum diffusivity to turbulent thermal diffusivity

Answer

The turbulent Prandtl number (Pr_t) represents the ratio of eddy viscosity to eddy thermal diffusivity, typically assumed near 0.85-0.9 for gases in wall-bounded flows.

Question 4

In CFD simulation of compressible flow, what occurs at a normal shock wave within the computational domain?

Accepted Answer

Abrupt discontinuity in velocity, pressure, and temperature

Answer

A normal shock represents an abrupt discontinuity where flow transitions from supersonic to subsonic with sudden increases in pressure, temperature, and density and decrease in velocity.

Question 5

What is the primary advantage of Detached Eddy Simulation (DES) over standard RANS turbulence models?

Accepted Answer

DES resolves large-scale turbulent structures in separated flow regions

Answer

DES uses RANS near walls and switches to LES-like treatment in separated regions, better capturing large-scale unsteady turbulent structures in wakes and separated shear layers.

(CPCE) Certified Professional CFD Engineer Practice Test

(CPCE) Certified Professional CFD Engineer Practice Test

CPCE Fluid Flow & Heat Transfer Analysis 5