water hammer simulation

[ferchuvicente]

hi, i have to simulate a water efect (in this case is a hot-oil circuit impulsed by a pump) and i would like to know what are going on with the pipe when switch of the pump.
Can i simulate this phenomena wiht CFX?

REGARDS

 

[c2sco]

There is lots of custom software for analysing water hammer due to pump trips, but most are complex and expensive (see Flowmaster, AFT Impulse, etc) However there's an inexpensive one that I can recommend - go to

http://www.istec.com.uy/eng/products/hitrans/

I have done modelling of pump trips with this software and validated it against the same models written in Flowmaster and it gives good answers but needs to be used with care as if you get cavitation then the results are inaccurate after cavitation starts. The same is true of the expensive software I suspect - it's always best to design to prevent cavitation.
More info on my web site if you're interested -

http://www.process-notes.co.uk

Regards,
Stuart

 

[drjrice]

I'm familiar with CFX and I believe you can use it to model water hammer. Water hammer is of course a pressure wave. In most situations water is treated as an incompressiblle fluid which implies infinite sound speeds. To model water hammer, you would have to treat the water as being compressible and perform a transient analysis.

 

[cloche]

Exactly, Drjrice.
At my company most CFD calculations are based on CFX, but for transients we use custom-made programs based on analytical formulas. Anyway, the principle is always the same: water as compressible, wave propagation equations, energy conservation / dissipation equations, etc... = transient analysis!
If the need is to estimate waterhammer transients, with a global error of less than 10% but local errors which can reach 100% (i.e. you will only calculate avg wh pressure), you can rely on analytical formulas in my opinion...

 

[mfontenot29]

Another option is to use Sinda/Fluint by Cullimore and Ring technologies. This is a ciruit type analysis program similar to AFT's Fathom/Arrow and not geometry based like a CFD program.

However, this program handles steady/transient/single phase/two phase flow with heat transfer and has empty subroutine blocks which you can use to manipulate valve, pump, etc. parameters as a function of time.

Although not user friendly, it cost about the same as a single AFT product with much more horsepower. It's engine was originally developed by NASA, I believe.

Hope this presents a useful option for you.