An engineer's pipe flow

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(Start of a small tutorial on how to calculate flows in arbitrary pipes.)
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Revision as of 22:56, 31 January 2008

Velocity results of our example
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Velocity results of our example

All these oceans with their tides and ships cuising in it are impressive, aren't they? Did you notice how stiff and probably refreshing the breeze around MS Tangaroa is?

Well, as an ordinary mechanical engineer I often have much less impressive things to work out. Like water taps, curved pipes or some sort of flow meter. These small-sized internal flows are, what this tutorial is about. I'll take an example on a simple pipe with two bows in it.

In this tutorial I'll explain how to get more or less arbitrary geometry of internal flows into the Gerris flow solver and how to compute the fluid's behavior there. I'll discuss on what's all this fuss with the Reynolds Number is and how it translates to simple engineering tasks. Finally, I'll do some basic measures in the results and will compare against what a textbook on hydraulics considers as the correct solution.

Contents

Computer Aided Design

Undoubtly, different engineers have different tastes about what a good software package for doing CAD is. So, I'll keep this part short and will explain how the result should look, only.

The few steps mentioned here sound simple, but can be a lot of work, of course:

  1. Create a model of where in your design the fluid flows.
  2. Create a cube of arbitrary, but known size to cover this fluid model.
  3. Substract the modeled fluid flow from this cube.
  4. Make sure the inlet and outlet of this flow reaches the cube's sides.

The result might look like this:

Our example in CAD
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Our example in CAD

Additional requirements for your CAD work:

  • All of the cube's edges should be of equal size (or it wouldn't be a cube).
  • It's only one inlet or outlet per cube side allowed.
  • Avoid trapped volumes as it's a waste of computing time.


From CAD geometry to Gerris geometry

A simple calculation script

Calculating and viewing results

Is it water or is it air: physical properties

Putting two checkpoints in

What the textbook says to such a case

Discussion of the differences between Gerris and the textbook

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