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Old   May 31, 2010, 06:19
Question Plunging airfoil + Flapping wing
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Sony
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Hi all !

I am solving a 2D sinusoidally plunging airfoil.
I have an airfoil surronded by fluid domain which is moving with the airfoil and they are plunging in a stationary fluid domain. I have given plunging motion through CEL.

I am getting negative volumes, after about 30 time steps.
I have tried different modal exponent values for mesh stiffness, smaller time steps, but the problem persists.

Could some please suggest how to get rid of this problem?
Also could flapping wing model in CFX?

Thanks in advance
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Old   May 31, 2010, 07:27
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Glenn Horrocks
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This is possible but difficult using the moving mesh approach. You can use a clever local smoothing function around the airfoil but it is tricky to get working.

A better approach is often to put the airfoil in a rotating frame of reference and connect it to the surroundings with a GGI. If you need to add translation you can make a section slide. If this type of approach is valid for you motion it is very good as it means you don't deform the mesh at all (but to do the translation you still need moving mesh).

This can also be done using immersed solids. This is by far the easiest approach but you will loose boundary layer fidelity and for airfoils that is usually critical.
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Old   June 9, 2010, 22:26
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Thanks Glen,
I will try out your suggestions.

Cheers.
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Old   June 15, 2010, 04:17
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Hi Sony

I am working on plunging airfoil also. I am trying to simulate transition too.
I have some questions please
First of all about UDF, what is the format of this file? I have write a code as UDF but fluent does not understand it.
Second, about transition point. how can I set transition point in dynamic mesh?
Third, how can I define airfoil as moving boundary? could you please describe more extensively?
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Old   June 15, 2010, 06:49
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For questions about Fluent try http://www.cfd-online.com/Forums/fluent/
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