CFD nozzle simulation

[Anonymous]

Hi all,

Apologies if this is a simplistic query - I have never used Autodesk and do not have a background in Computational Fluid Dynamics. I am currently downloading Autodesk CFD but wanted to know whether this was possible/easy to do so before I started doing any work on this!

I am currently constructing a rainfall simulator (using Antelco Vari-Jet misting nozzles - http://www.antelco.com/uk/pdfs/Vari%20Jets.pdf) and saw a document which had a CFD-simulation showing the outflow from one of the nozzles. I was wondering - is this easy to produce one of these figures (especially for someone who has never used CDF before!) and what variables would I need to produce this (e.g. I guess inlet size, pipe size, pressure etc.)?

Look forward to hearing from you and once again, apologies in advance!

Kind regards,

Dan

[Jon.Wilde]

Hi Dan,

I would say that you have found one of the things that CFD is less suitable for. It is a great and easy to use package but we would not be able to model a mist very well. Although we have the ability to model a free surface flow, we do not capture air resistance or surface tension, both of which will be critical here.

If you were to assume a single fluid, air or water - then we could model this with ease.

Hope that helps,

Jon

[Anonymous]

Hi Jon,

Thank you for your reply and for the useful response.

That's a shame that CFD would not be able to capture air resistance or surface tension when modelling the nozzle outflow and I understand that these factors would be critical when modellng the flow from a misting nozzle.

If I was to assume a single fluid, i.e. water, outputting from the nozzle, would the outputs of the simulation be significantly erroneous or would this give me a rough indication of the nozzle outflow characteristics? I'm interested in gaining an understanding of the spray characteristics (i.e. spray diameter, outflow etc.) within a laboratory setting, i.e. no-wind etc.. If this is worth doing, is this fairly easy for a complete novice to CFD? If not, do you recommend any other methods?

Kind regards,

Daniel

[Royce_adsk]

Don't think there is much here we can help with. If you were to only model the fluid through he device before it enters into the outside air domain, maybe there is something we can help with.  Can review the flow rates/speeds leaving the device and try to correlate that to how it would function outside of the spray nozzle in the laboratory environment.

[Jon.Wilde]

I wanted to share this from one of our team members too, might give you a little more to think about:

I think the one area we can help with would be the spray diameter and general pattern shape. Thinking about what actually goes on inside a nozzle, we are generally simulating reality right up until the exit region of the device. It’s the upstream geometry that has an impact on the resultant spray pattern for most nozzles, which is why we can effectively predict the pattern with the assumption of a single fluid domain. The fluid velocities downstream of the nozzle will likely be much higher in reality vs simulation, particularly as you get further out in the throw. Pushing water into water is pretty restrictive compared to water into air. That said, we should do a good job with the overall pattern prediction.

The only issue we could have would be simulating some sort of low speed phenomenon like the complex fluid formations from a water faucet or dynamic changes like water droplets forming/deforming in the mist region.

Hopefully this proves useful.

Kind regards,

Jon