# Computational Fluid Dynamics 5

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```					Computational Fluid Dynamics 5
Professor William J Easson
School of Engineering and Electronics
The University of Edinburgh

www.see.ed.ac.uk/~bille
Aim
To provide the engineer with the
understanding and practical experience
required to use commercial
CFD software for solving real engineering
problems
Objectives
• to learn how to solve problems in fluid dynamics
using a commercial CFD code
• to understand sufficiently the underlying fluid
dynamics to appreciate the scope and limitations
of the solutions
• to be able to assess the errors involved in CFD
simulation
• To be able to interpret and present the results in an
appropriate professional context
Recommended texts
• Anderson, JD: Computational Fluid Dynamics
– well written text excellent introduction
– uses finite difference approach
• Versteeg, HK and Malalasekera, W: An
Introduction to CFD
– good finite volume intro
– Content a little out-of-date
• Ferziger, JH and Peric, M
– Excellent treatise on finite volume method for the
mathematics and fluids expert
Course structure
• Wednesday 10am-10.50am, weeks 1-8
– Lecture (Ashworth 3)
• Wednesday 11.10am-1pm
– Practical (TLG)
• Week 5
– Assessment 1 (10%)
• Week 11
– Assessment 2 (40%)
• Week 13
– Examination (50%)
• Nb all dates approximate at present
How does a CFD code work?
• Preprocessor
– create geometry
– mesh volume
• Processor
– solve a system of equations
– approximation to subset or superset of Navier-Stokes
equations
• Post-processor
– Vector plots, contour plots, integrated values (eg total
pressure)
– Colour For Directors
Ultrasound scan of carotid artery
Creating a
3D voxel
image
Carotid image surface rendered
Carotid surface mesh
• Two examples
• ShIRT (left)
• Rhino (right)
Velocity
streamlines
(as ribbons)
Shear stress on walls
Steps to CFD
1. Divide the fluid volume (surface) up into
manageable chunks (gridding)
2. Simplify the equations to be solved
3. Set boundary conditions
4. Initialise the other grid values
5. Step through the grid ensuring that these
simplified equations are satisfied at the
grid points and nearest neighbours
Trivial example (u=a + bx)

u

0   1   2   3   4   x
Getting started
• Star-CCM+ running on Linux
• One licnese per CFD5 student – rest are for
researchers
• Commercial cost is c. £20k per seat
• 3D simulations take a long time to mesh/run
• We will mainly use 2D
Star-CCM+
• New to Edinburgh
• Used to use Fluent but costs now too high
• You and I will be learning the software at the
same time!
• Things to do before next Wednesday
– Login to the Linux environment
– Familiarise yourself with some basic commands
– Run some of the Star-CCM+ tutorials after I email you!
Some basic linux commands
• mkdir <filename>
– creates a new directory where you are
• cd <filename>
– moves to a directory
• rm <filename>
– deletes a directory or file
• pwd
– in case you’re lost this shows you where in the
directory structure you are (literally present working
directory)
Any questions?

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