CPCE CPCE Turbulence Modeling & Numerical Methods 2

Question 1

What is 'numerical diffusion' in CFD and how does it typically arise?

Accepted Answer

Artificial smearing of gradients introduced by low-order upwind discretization

Answer

Numerical diffusion is artificial smearing of flow gradients caused by truncation errors in low-order (e.g., first-order upwind) discretization schemes.

Question 2

In Reynolds-Averaged Navier-Stokes (RANS) simulations, what does the Reynolds decomposition separate the flow variables into?

Accepted Answer

Mean and fluctuating components

Answer

Reynolds decomposition splits each flow variable into a time-averaged mean component and a fluctuating component, enabling the RANS approach to turbulence modeling.

Question 3

Which iterative solver is widely used in CFD for solving large sparse linear systems arising from pressure-velocity coupling?

Accepted Answer

Conjugate Gradient (CG) method

Answer

The Conjugate Gradient method and its preconditioned variants are widely used for solving large sparse symmetric linear systems in CFD pressure solvers.

Question 4

What is the purpose of the SIMPLE algorithm in CFD?

Accepted Answer

To couple the pressure and velocity fields in incompressible flow solvers

Answer

The SIMPLE (Semi-Implicit Method for Pressure-Linked Equations) algorithm iteratively solves coupled pressure and velocity equations for incompressible flows.

Question 5

In the context of CFD numerical methods, what is 'upwinding'?

Accepted Answer

Using information from the upstream side when discretizing convection terms

Answer

Upwinding biases the discretization of convection terms to use values from the upwind (upstream) direction, improving numerical stability by respecting the direction of information propagation.

(CPCE) Certified Professional CFD Engineer Practice Test

(CPCE) Certified Professional CFD Engineer Practice Test

CPCE CPCE Turbulence Modeling & Numerical Methods 2