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   – Content a little out-of-date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
• 60 seats licensed
• 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?