CFD - Introduction

Question 1

Analytical Method

Answer 1

Obtain exact solutions of approximate equations (exist only for a few cases under certain assumptions).

Question 2

Experimental Investigations

Answer 2

Full-Scale Testing:

Expensive, sometimes impossible, measurement uncertainties.

Small-Scale Model:

Simplified and difficult to extrapolate results, measurement uncertainties.

Question 3

Numerical Solution

Answer 3

Obtain approximate solutions of exact equations.

Exist for almost any degree of complexity.

Question 4

Applications of CFD

Answer 4

1. Aerodynamics of aircraft and vehicles
2. Hydrodynamics of ships
3. Biomedical Engineering (Blood flows, pulmonary flows)

Question 5

Principle of CFD

Answer 5

CFD employs numerical techniques to build algebraic equations to represent the original governing differential equations, then solves them on a grid.

Question 6

Pre-Processing

Answer 6

• Define the problem (fluid properties, governing equations, boundary conditions)
• Define the computational domain
• Generate a grid (or mesh) of cells (or control volumes of elements)

Question 7

Solving

Answer 7

• Discretisation of equations
• Solve equations simultaneously and iteratively

Question 8

Post-Processing

Answer 8

• Demonstrate, inspect and visualise results.

Quantities: forces, pressure distribution, heat transfer coefficients etc.

Question 9

Round-Off Error

Answer 9

Due to the finite word size of the computer (bits) - inevitable but small

Question 10

Truncation Error

Answer 10

Due to approximations in the numerical method, it will go to zero as the grid is refined

Question 11

Solution Dispersion

Answer 11

Local Oscillations

Question 12

Solution Dissipation

Answer 12

False Diffusion

Question 13

CFD solutions are only as good as…

Answer 13

The boundary conditions used, and the physical models used.