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simulation with two interacting airstreams, how to set up ?

Question asked by Thor Unbescheid on May 16, 2012
Latest reply on May 16, 2012 by Chris Michalski

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Hello forum,

I am new to Flow Simulation, and since we can use it at our university I tried to experiment with the following setup (image):

Two air flows from different directions. Flow one is 1.6 m/s. Flow two starts inside of the jet nozzle object and exits the nozzle with about 10-20 m/s. I am interested in how the two flows interact with each other, and if flow 2 can prevent flow 1 from reaching the object, or rather how fast flow 2 has to be to do so.

I think it is pretty simple but somehow I can't manage to get it to work. I tried it with a mixture of internal an external flows, and with two internal flows (modeling a huge box around it, but I didn't know excactly where to set the outlets).

If it is an external flow setup with an internal flow included, do i have to set a outlet lid on top of the nozzle? How could I get this to work ?

Thank you and have a nice day!

Thor

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Chris Michalski May 16, 2012 9:16 AM

Thor -

you will need to use an external simulation. External allows both internal and external flow conditions, but internal only allows internal flows.

You will set boundary conditions on the 2 solid surfaces such that the arrows point in the direction of flow and define either the velocity or mass flow rate, etc.

With an external simulation it will solve how those flows interact with the ambient out until the limits of your computational domain.

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Thor Unbescheid @ Chris Michalski on May 16, 2012 9:31 AM

Hello Chris,

thank you for your answer.

I tried it before, but when I display the flow trajectories it will only show the ones of the external flow. Maybe one out of 500 lines comes out of the nozzle. Moreover, the traj. lines of the external flow do not seem to be influenced by the nozzle flow.

Could this be because the mesh isn't dense enough ?

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Chris Michalski @ Thor Unbescheid on May 16, 2012 9:38 AM

have you tried making multiple trajectories to trace? one from each of the slots?

Or perhaps a better way would be to use 2 different fluids - use air as the default and the fluid from one slot, but use Nitrogen for the other. Because you are not doing a high-temperature study the difference between Nitrogen and Air will be insignificant but this will allow you to create a cut-plot to look at Mass Fraction of fluids. If you have a mix of gases near your object then you know that Flow 2 is not strong enough to prevent penetration by Flow 1.

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Chris Michalski May 16, 2012 9:16 AM
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Thor -

you will need to use an external simulation. External allows both internal and external flow conditions, but internal only allows internal flows.

You will set boundary conditions on the 2 solid surfaces such that the arrows point in the direction of flow and define either the velocity or mass flow rate, etc.

With an external simulation it will solve how those flows interact with the ambient out until the limits of your computational domain.
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- Thor Unbescheid @ Chris Michalski on May 16, 2012 9:31 AM
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  Hello Chris,
  
  thank you for your answer.
  I tried it before, but when I display the flow trajectories it will only show the ones of the external flow. Maybe one out of 500 lines comes out of the nozzle. Moreover, the traj. lines of the external flow do not seem to be influenced by the nozzle flow.
  Could this be because the mesh isn't dense enough ?
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  - Chris Michalski @ Thor Unbescheid on May 16, 2012 9:38 AM
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    have you tried making multiple trajectories to trace? one from each of the slots?
    
    Or perhaps a better way would be to use 2 different fluids - use air as the default and the fluid from one slot, but use Nitrogen for the other. Because you are not doing a high-temperature study the difference between Nitrogen and Air will be insignificant but this will allow you to create a cut-plot to look at Mass Fraction of fluids. If you have a mix of gases near your object then you know that Flow 2 is not strong enough to prevent penetration by Flow 1.
    Like • Show 0 Likes0
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simulation with two interacting airstreams, how to set up ?

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