CPCE Fluid Flow & Heat Transfer Analysis 2 — Questions and Answers
Question 1: In CFD, the SIMPLE algorithm stands for which pressure-velocity coupling method?
- Semi-Implicit Method for Pressure-Linked Equations (Correct answer)
- Structured Implicit Multi-Phase Linearization Equations
- Sequential Iterative Method for Pressure-Level Estimation
- Staggered Implicit Method for Pressure and Laminar Equations
Correct answer: Semi-Implicit Method for Pressure-Linked Equations
SIMPLE (Semi-Implicit Method for Pressure-Linked Equations) is the most widely used pressure-velocity coupling algorithm in incompressible flow solvers.
Question 2: What dimensionless number governs the ratio of inertial forces to viscous forces in a fluid flow?
- Nusselt number
- Prandtl number
- Reynolds number (Correct answer)
- Grashof number
Correct answer: Reynolds number
The Reynolds number Re = ρVL/μ characterizes the ratio of inertial to viscous forces and determines whether flow is laminar or turbulent.
Question 3: Which boundary condition type specifies a known heat flux at a wall in a CFD heat transfer simulation?
- Dirichlet boundary condition
- Neumann boundary condition (Correct answer)
- Robin boundary condition
- Periodic boundary condition
Correct answer: Neumann boundary condition
A Neumann boundary condition specifies the gradient of the dependent variable (heat flux) at the boundary rather than the value itself.
Question 4: In turbulent flow CFD modeling, what does the k-ε turbulence model solve for?
- Kinematic viscosity and energy dissipation rate
- Turbulent kinetic energy and its dissipation rate (Correct answer)
- Thermal conductivity and eddy viscosity
- Vorticity and strain rate tensors
Correct answer: Turbulent kinetic energy and its dissipation rate
The k-ε model solves two transport equations: one for turbulent kinetic energy (k) and one for its dissipation rate (ε).
Question 5: For a flat plate in forced convection, how does the local heat transfer coefficient vary along the plate in the laminar boundary layer regime?
- It increases with distance from the leading edge
- It remains constant along the plate
- It decreases with distance from the leading edge (Correct answer)
- It first increases then decreases with distance
Correct answer: It decreases with distance from the leading edge
The local heat transfer coefficient decreases along the plate as the thermal boundary layer grows thicker with downstream distance in laminar flow.
Question 6: What is the primary purpose of using a staggered grid arrangement in CFD pressure-velocity coupling?
- To increase computational speed
- To prevent checkerboard pressure oscillations (Correct answer)
- To simplify boundary condition implementation
- To improve turbulence model accuracy
Correct answer: To prevent checkerboard pressure oscillations
Staggered grids store velocity components at cell faces and pressure at cell centers, preventing the checkerboard pressure-velocity decoupling problem.
Question 7: Which heat transfer mechanism is dominant in liquid metals due to their very low Prandtl number?
- Convective heat transfer
- Radiative heat transfer
- Conductive heat transfer (Correct answer)
- Phase-change heat transfer
Correct answer: Conductive heat transfer
Liquid metals have very low Prandtl numbers (Pr << 1), meaning thermal diffusivity dominates momentum diffusivity, making conduction the dominant heat transfer mechanism.
CPCE Fluid Flow & Heat Transfer Analysis 2
In CFD, the SIMPLE algorithm stands for which pressure-velocity coupling method?