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Compressible flow with free surface?

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Old   January 17, 2011, 06:43
Default Compressible flow with free surface?
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mediode
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Dear forum,

is Flow3D capable to realize compressible flow together with a free surface? I am thinking about filling of cavities during injection moulding. Has anybody tried this or is just not possible?

Thanks in advance

m*
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Old   January 17, 2011, 14:14
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michael barkhudarov
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You mean to include air as the compressible fluid? This can be done using the two-fluid model with sharp interface. Only fluid #2 can be compressible.

You could also add limited compressibility to fluid #1, using either one- or two-fluid model, based on the speed of sound. Check it out in the Manual.
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Old   January 18, 2011, 05:22
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Hello,

plastics injection moulding would require the fluid to be compressible, entering the "empty" cavity, filled with air. The counterepressure of the contained air could be disregarded in the first stage ....

So, the setup should be 1 compressible fluid with free surface, according to the metal casting simulations, where usually 1 incompressible fluid with free surface is handled - just compressible instead of incompressible. Is that possible?

Best regards

M*
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Old   January 18, 2011, 12:56
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Quote:
Originally Posted by mediode View Post
Hello,

plastics injection moulding would require the fluid to be compressible, entering the "empty" cavity, filled with air. The counterepressure of the contained air could be disregarded in the first stage ....

So, the setup should be 1 compressible fluid with free surface, according to the metal casting simulations, where usually 1 incompressible fluid with free surface is handled - just compressible instead of incompressible. Is that possible?

Best regards

M*
The fully compressible flow model in FLOW-3D assumes gas, s there can be no free surface. The limited compressibility model assumes a linear relationship between pressure P and density rho:

dP=c^2*d(rho)

where c is the speed of sound in the fluid. This can be used for one-fluid, free-surface flows, like your filling.

Would this work for you? What is the equation of state for the plastics?
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Old   January 19, 2011, 16:07
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Thank you for your suggestions! I' ll keep you updated about my progress ...
Best regards
m*
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Old   January 20, 2011, 06:21
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A technical note on injection moulding of polymer material:
http://www.flow3d.com/pdfs/tn/FloSci-TN34.pdf
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