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 Mark Wisom July 25, 2002 06:34

Flow through a pipe problem

Hi All,

My problem is that I have a product that needs to be oil cooled and I have some CFD work that I haven't got a clue where to start. Basically I have a pipedblocked off at one end and a pump on the other end pumping oil in. Then there are a number of holes in the pipe where the oil squirts out of (into a chamber of oil at a different pressure). It's sort of like a garden sprinkler. Anyway I have to work out the velocites at which the oil comes out of these holes. We have modelling software but in reality there will be hundreds of holes in this pipe and we don't have the computing power for that.

Any idea what hand-calculations I can do to get some idea of the velocities of the oil as it leaves through the holes.

Thanks Mark

 Thomas P. Abraham July 25, 2002 07:15

Re: Flow through a pipe problem

Hello Mark,

Try something like FLOWMASTER. This approach should not be too intensive computationally.

Thanks,

Thomas

 Volker July 25, 2002 10:03

Re: Flow through a pipe problem

Hi,

For an easy hand-calculation, just take the flow rate of your oil and the total area of holes to calculate the average velocity. If your pipe isn't very long, the holes of the same diameter, the velocity in the pipe not too high and the surrounding pressure uniform, this should give you a reasonable result. If that is too trivial, you can try and simulate a segment of the pipe

Hope that helps,

Volker

 babyface July 25, 2002 12:18

Re: Flow through a pipe problem

Your case must be 3D which means time consuming. Try using the periodic BCs to reduce the whole grids

Regards

 Jim Park July 25, 2002 13:20

Re: Flow through a pipe problem

You may find it useful to assume that the flow in the pipe is just that; parabolic pipe flow. That's essentially a one-dimensional analysis (pressure is constant across any section of the pipe). Solve the parabolic distribution with an unknown outflow velocity along the wall - to do this assume that the wall is uniformly porous. You can try assuming that the radial distribution of flow out of the pipe is uniform. Note that the assumptions are better if the pressure drop across the pipe wall is a large fraction of the overall pressure drop serviced by your pump. This is all pen-and-paper analysis.

If you equate the mass flow through the (hypothetical) porous wall with the total flow through the holes [as suggested above], you should be able to work out an effective permeability to model flow through the wall as a function of the pressure drop. You can use this to express the pressure drop and flow across the wall as functions of the pressure drop along the inside of the pipe. Eventually, I think all the algebra leads to direct coupling of the supply pressure to conditions inside your low pressure tank. This removes the pipe and holes from the computational problem.

The remaining problem of flow in the low pressure volume can be solved using CFD. The velocities you seek come from that solution.

The devil's in the details. Good luck!

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