First Step To Take Project In CFD

Saturday, August 4, 2012

A good question comes from reader of this blog, what is the first step for him to do to take project in CFD?.

He feels, like anyone else i guess, learning fundamental of CFD in Transport Phenomena is too much. Anyone wants practical ways to do this. So, based on my experience, here’s what you need to do

1. Specify your Project well

For example, you want to simulate mixing in a tank with gases. So, you will need drawing a tank, blade, baffle (maybe) and porous ring for gases to inject. Draw this on a paper. Put metric record beside your drawing. Specify completely, for example for baflle, you need to specify baffle thickness, number of baffle, baffle clearance etc. Here’s some record:

Tank : Diameter, Height, bottom shape (including it’s size if curved)

Baffle : number of baffle, clearance from bottom, clearance from tank wall, thickness etc

Blade : shape, inner and outer diameter, blade thickness, blade tip form, Rod diameter, rod position (center or off center).

Porous ring : ring shape, bottom clearance, diameter, hole number and diameter) etc.

Why you should need this measurement first?. Because you’ll need everything in drawing to be exactly as in real mixer.

2. Try to draw your equipment in exact, and if failed, simplify your drawing

It’s not only matter of drawing what you concern, but your drawing must be able to grid (slice into small pieces). There’s some limitation in gridding capability both on Gambit or using other software, in complex drawing, you must ‘DIRECT" the program how to grid. Well, The challenge is just begin.

Gridding session is painful step in my experience, if you don’t know the nature of program you use. Open again and again Modelling Guide (if you using Gambit), and try to locate where your shape cannot be grid. If you stuck in gridding, you better simplify your drawing.

For example, perforated ring, it’s difficult to draw small hole in a ring. You better specify an area over ring to gas to be injected.

3. Specify Boundary Condition

In specifying boundary condition, you must understand the nature of each boundary condition. For example wall, flow input, porous etc. Read well the guide or ask your supervisor

4. Try Import to Fluent

Importing to fluent sometimes failed. For example when your grid skewness cannot be accepted. Or your drawing overlapping if you use 2 drawing block and combined together in fluent. As guidelines, try to grid using hexagonal, it’s easier to import. So, after gridding, save your grid and try to import to fluent.

5. Run Simulation

In running your simulation, you must understand that not each of the method available in program, suitable for your case. Choose one, or choose the best. Read much paper about your simulation first and check their method, try to use them, before advance to your own method

6. Reporting

Simulation usually lasted for 3-7 days depend on the computer speed and your grid size. After simulation ended, you’ll need to report your simulation result. Sometimes you’ll need to virtually slice the tank and take data from specific location. It can be done if you read guideline well.

Next post, I’ll try to explain the step in real project..

Good Luck.