Relative velocity in Air-Blast Atomizer

  • Last Post 22 November 2018
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Cybex posted this 21 November 2018

Fluent 18.2

In Air-Blast Atomizer point properties, does anyone know what "Relative velocity" precisely refers to? How does it affect the characteristics of droplets (such as velocity and diameter) being sprayed from the atomiser? Does it also affect the velocity of gases (defined e.g. as boundary conditions) used to break droplets? In the User's Guide there is no clear explanation about this.

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rwoolhou posted this 21 November 2018

Assuming there are no moving parts in the system it's the speed that the spray is entering the system at.  If you have moving parts then it's the speed relative to that motion if the injection is associated with that part of the model: I agree it could be clearer but haven't yet seen a better option. 

The gas velocity is assigned via inlets etc and does not enter the domain through the injection: hence you need to be careful with the model set up to make sure there's air available to provide the break up etc. 

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Cybex posted this 21 November 2018

Thank you for your reply.

Considering a stream of nitrogen behind the atomiser (defined to provide the break up as you said), what would the spray velocity be? The one of nitrogen plus the Relative velocity parameter?

seeta gunti posted this 22 November 2018

Hope this pic will give you more idea on relative velocity.

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abenhadj posted this 22 November 2018

The (maximum) relative velocity is the one between the sheet and the air. This has to be as input for the Air-Assist Atomizer unlike the Swirl Atomizer.

Best regards,